Bochs/bochs/doc/docbook/development/development.dbk

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doc/docbook/development/development.dbk
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This is the top level file for the Bochs Developers Manual.
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<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook V4.1//EN" [

<!-- include definitions that are common to all Bochs documentation -->
<!ENTITY % bochsdefs SYSTEM "../include/defs.sgm">
%bochsdefs;

]>
<book>
<bookinfo>
   <title>Bochs Developers Guide</title>
   <authorgroup>
   <author><firstname>Kevin</firstname><surname>Lawton</surname></author>
   <author><firstname>Bryce</firstname><surname>Denney</surname></author>
   <author><firstname>Christophe</firstname><surname>Bothamy</surname></author>
   <editor><firstname>Michael</firstname><surname>Calabrese</surname></editor>
   </authorgroup>
</bookinfo>

<!-- *************************************************************** -->
<chapter id="resources"><title>Resources for developers</title>
<para>
The development guide describes resources that are intended for developers
in particular.  Many Bochs resources are also covered in the User Guide,
including compile instructions, bochsrc options, how to find the mailing
lists, etc.
</para>

<section id="svn-write-access-setup"><title>Setting up SVN write access</title>
<para>
If you are an official SourceForge developer, then you can use SVN with write
access.  The SVN contains the most recent copy of the source code, and with
write access you can upload any changes you make to the SVN server for others
to use. The SVN checkout command is identical to the one for normal users, but
you might want to get the whole tree to work with branches and tags.
</para>

<screen>
  <command>svn co https://svn.code.sf.net/p/bochs/code bochs-svn</command>
</screen>

<para>
Depending on your network connection this may take a long time, since it downloads all
files from all branches and tags that ever have been created.
</para>

</section> <!-- end setting up svn write access -->

<section id="using-svn-write-access"><title>Using SVN write access</title>

<section><title>Checking in files</title>
<para>
Once you have a Bochs directory, you can compile the files, edit them, test them, etc.
See the documentation section, <ulink url="../user/get-src-svn.html">Tracking the source code with SVN</ulink>
for more info on SVN, in the User Manual. But what's new and different is that
you can now do SVN commits. When a file is all fixed and ready to share with the rest of
the world, you run a commit command to upload your version to the server.
First, it's good to do a SVN update to make sure nobody else has changed it
since you downloaded it last. At the first commit you'll always have to specify your
SF username and type your password.
</para>

<screen>
  $ svn update file.cc
  $ svn commit --username <replaceable>sfusername</replaceable> file.cc
  [editor opens. type log message, save, and exit.]
  Login area: &lt;https://svn.code.sf.net:443&gt; SourceForge Subversion area
  Username: <replaceable>sfusername</replaceable>
  Password for '<replaceable>sfusername</replaceable>': <replaceable><--type your password</replaceable>
  Sending        file.cc
  Transmitting file data .
  Committed revision 10.
</screen>

<para>
When SVN starts an editor, The default is usually vi. If you want a different
editor, set the EDITOR environment variable to the name of your preferred
editor.  When you're done, just save the file and quit the editor.  Unless
there's some problem, you will see a message that says what the new SVN revision
number is, and then "done".  If while you're editing the log message, you decide
that you don't want to commit after all, don't save the file. Quit the editor,
and when it asks where the log message went, tell it to abort.
</para>

<para>
Here is an example of a successful checkin:

<screen>
  $ svn commit misc.txt
  [edit log msg]
  Sending        misc.txt
  Transmitting file data .
  Committed revision 6.
</screen>

And here is an aborted one:

<screen>
  $ svn commit misc.txt
  [quit editor without saving]
  Log message unchanged or not specified
  a)bort, c)ontinue, e)dit:
  a
</screen>

</para>
</section> <!--end of "Checking in Files" -->

<section><title>Creating a backup of the SVN repository</title>
<para>
Backups of the SVN repository can be made with the <command>rsync</command> utility.
In case of data corruption or other problems on the server, the repository with all
revisions, branches and tags can be restored easily. It is recommended to update this
backup frequently. The following example creates a folder called
<filename>bochs-svn-rsync</filename> that contains the repository.
<screen>
  rsync -av svn.code.sf.net::p/bochs/code bochs-svn-rsync
</screen>
</para>
</section>

<section><title>Setting SVN commit notifications</title>
<para>
The Bochs SVN repository is set up to send a notification email to the "bochs-cvs"
mailing list after each successful commit. This email contains the log message, a list
of the modified files and a diff against the previous revision. The diff of large
commits will be truncated at 96 kByte.
</para>
<para>
After each commit the SVN server runs the script <command>post-commit</command> located
in the <filename>hooks</filename> folder. On SourceForge, this script forces a refresh
of the Allura code browser and it can call a script <command>post-commit-user</command>
for addition operations if it exists. For Bochs we have set up this script and call
<command>svnnotify</command> from it to create the notification email.
<screen>
#!/bin/sh

svnnotify --repos-path $1 --revision $2 -O -C -d -e 98304 -t bochs-cvs@lists.sourceforge.net
</screen>
</para>
</section>

</section> <!--end of "Using SVN write access" -->

      <section id="trackers"><title>SourceForge bug, feature, and patch trackers</title>
         <para>
          &FIXME;
         </para>
      </section>

<section id="other"><title>Ideas for other sections</title>
<para>
<screen>
Ideas:
- how to browse code with the Allura code browser
- how to find an identifier, variable, or specific text in the code
- how to make patches with SVN
</screen>
</para>
</section>

</chapter>

<chapter id="about-the-code"><title>About the code</title>

<section id="code-overview"><title>Overview</title>
<para>
The initial versions of some sections in this chapter are based on a document
written by Peter "Firefly" Lund. It was added and updated in January 2006.
</para>
<para>
The Bochs virtual PC consists of many pieces of hardware. At a bare minimum
there are always a CPU, a PIT (Programmable Interval Timer), a PIC
(Programmable Interrupt Controller), a DMA controller, some memory (this
includes both RAM and BIOS ROMs), a video card (usually VGA), a keyboard port
(also handles the mouse), an RTC with battery backed NVRAM, and some extra
motherboard circuitry.
</para>
<para>
There might also be an ethernet card, a PCI controller, a soundcard,
an IDE controller (+ harddisks/CDROM), a SCSI controller (+ harddisks), a
floppy controller, an APIC ...
</para>
<para>
There may also be more than one CPU.
</para>
<para>
Most of these pieces of hardware have their own C++ class - and if Bochs is
configured to have more than one piece of a type of hardware, each will have
its own object.
</para>
<para>
The pieces of hardware communicates over a couple of buses with each other -
some of the things that the buses carry are reads and writes in memory space,
reads and writes in I/O space, interrupt requests, interrupt acknowledges, DMA
requests, DMA acknowledges, and NMI request/acknowledge. How that is simulated
is explained later.&FIXME;
</para>
<para>
In addition to the simulator itself, some other components are required for
the communication with the user. The most important parts are these:
<itemizedlist>
<listitem><para>the window that simulates the monitor and receives keyboard / mouse events</para></listitem>
<listitem><para>the configuration interface that allows to adjust simulation settings</para></listitem>
<listitem><para>the simulator interface for the communication between the other componnents</para></listitem>
<listitem><para>the parameter tree (for configuration settings and save/restore)</para></listitem>
<listitem><para>the logfunctions class (handle and configure panic/error/info/debug)</para></listitem>
</itemizedlist>
These componnents of Bochs are optional:
<itemizedlist>
<listitem><para>the plugin interface</para></listitem>
<listitem><para>the builtin debugger</para></listitem>
<listitem><para>the disassembler</para></listitem>
<listitem><para>the instrumentation feature</para></listitem>
</itemizedlist>
</para>
<para>
The simulation window is handled by the GUI object (other terms used in the
sources are "display library", "VGAW"). There are many different but compatible
implementations of the GUI object, depending on whether you compile for X (Unix/Linux),
Win32, Macintosh (two versions: one for Mac OS X and one for older OS's), Amiga,
etc. The cross-platform libraries SDL and wxWidgets are also supported.
</para>
<para>
For the configuration interface there are also some different implementations: textconfig
(text menus only), wxdialog (wxWidgets port), win32dialog/win32paramdlg (Windows port).
</para>
</section>

<section id="directory-structure"><title>Directory Structure</title>
<para>
<table>
<title>Directory structure</title>
<tgroup cols="2">
<thead>
<row>
<entry>Location</entry>
<entry>Meaning</entry>
</row>
</thead>
<tbody>
<row><entry>bios</entry><entry>System and VGA BIOS images, system BIOS sources and makefile</entry></row>
<row><entry>build</entry><entry>additional stuff required for building Bochs on different platforms</entry></row>
<row><entry>bx_debug</entry><entry>the builtin Bochs debugger</entry></row>
<row><entry>cpu</entry><entry>the cpu emulation sources</entry></row>
<row><entry>cpu/fpu</entry><entry>the fpu emulation sources</entry></row>
<row><entry>disasm</entry><entry>the disassembler for the Bochs debugger</entry></row>
<row><entry>doc/docbook</entry><entry>the Bochs documentation in DocBook format</entry></row>
<row><entry>doc/man</entry><entry>Bochs manual pages</entry></row>
<row><entry>docs-html</entry><entry>old Bochs documentation in HTML (will be replaced by DocBook)</entry></row>
<row><entry>gui</entry><entry>display libraries (guis), the simulator interface and text mode config interface</entry></row>
<row><entry>gui/bitmaps</entry><entry>bitmaps for the headerbar</entry></row>
<row><entry>gui/font</entry><entry>the default VGA font used by most of the display libraries</entry></row>
<row><entry>gui/keymaps</entry><entry>keymaps for the keyboard mapping feature</entry></row>
<row><entry>host</entry><entry>host specific drivers (currently only used by the pcidev kernel module for Linux)</entry></row>
<row><entry>instrument</entry><entry>directory tree for the instrumentation feature</entry></row>
<row><entry>iodev</entry><entry>standard PC devices, PCI core devices</entry></row>
<row><entry>iodev/display</entry><entry>display adapters (vga, cirrus, voodoo)</entry></row>
<row><entry>iodev/hdimage</entry><entry>support for different disk image types and lowlevel cdrom access</entry></row>
<row><entry>iodev/networking</entry><entry>networking devices and lowlevel modules</entry></row>
<row><entry>iodev/sound</entry><entry>sound devices and lowlevel modules</entry></row>
<row><entry>iodev/usb</entry><entry>USB HCs and pluggable devices</entry></row>
<row><entry>memory</entry><entry>memory management and ROM loader</entry></row>
<row><entry>misc</entry><entry>useful utilities (e.g. bximage, bxcommit, niclist)</entry></row>
<row><entry>misc/sb16</entry><entry>tool to control the SB16 emulation from the guest side</entry></row>
<row><entry>patches</entry><entry>pending patches</entry></row>
</tbody>
</tgroup>
</table>
</para>
</section>

<section id="emulator-objects"><title>Emulator Objects</title>
<section><title>Weird macros and other mysteries</title>
<para>
Bochs has many macros with inscrutable names. One might even go as far as to
say that Bochs is macro infested.
Some of them are gross speed hacks, to cover up the slow speed that C++ causes.
Others paper over differences between the simulated PC configurations.
Many of the macros exhibit the same problem as C++ does: too much stuff happens
behind the programmer's back. More explicitness would be a big win.
</para>
</section>
<section id="static-methods-hack"><title>Static methods hack</title>
<para>
C++ methods have an invisible parameter called the this pointer - otherwise the
method wouldn't know which object to operate on. In many cases in Bochs, there
will only ever be one object - so this flexibility is unnecessary. There is a
hack that can be enabled by #defining BX_USE_CPU_SMF to 1 in <filename>config.h
</filename> that makes most methods static, which means they have a "special
relationship" with the class they are declared in but apart from that are
normal C functions with no hidden parameters. Of course they still need access
to the internals of an object, so the single object of their class has a globally
visible name that these functions use. It is all hidden with macros.
</para>
<para>
Declaration of a class, from iodev/pic.h:
</para>
<screen>
...
#if BX_USE_PIC_SMF
#  define BX_PIC_SMF  static
#  define BX_PIC_THIS thePic->
#else
#  define BX_PIC_SMF
#  define BX_PIC_THIS this->
#endif
...
class bx_pic_c : public bx_pic_stub_c {

public:
  bx_pic_c(void);
  ~bx_pic_c(void);
...
  BX_PIC_SMF void   service_master_pic(void);
  BX_PIC_SMF void   service_slave_pic(void);
  BX_PIC_SMF void   clear_highest_interrupt(bx_pic_t *pic);
  };
</screen>
<para>
And iodev/pic.cc:
</para>
<screen>
...
#define LOG_THIS thePic->
...
bx_pic_c *thePic = NULL;
...
void bx_pic_c::service_master_pic(void)
{
  Bit8u unmasked_requests;
  int irq;
  Bit8u isr, max_irq;
  Bit8u highest_priority = BX_PIC_THIS s.master_pic.lowest_priority + 1;
  if(highest_priority > 7)
    highest_priority = 0;

  if (BX_PIC_THIS s.master_pic.INT) { /* last interrupt still not acknowleged */
    return;
  }

  if (BX_PIC_THIS s.master_pic.special_mask) {
    /* all priorities may be enabled.  check all IRR bits except ones
     * which have corresponding ISR bits set
     */
    max_irq = highest_priority;
  }
  else { /* normal mode */
    /* Find the highest priority IRQ that is enabled due to current ISR */
    isr = BX_PIC_THIS s.master_pic.isr;
...
}
...
</screen>
<para>
Ugly, isn't it? If we use static methods, methods prefixed with BX_PIC_SMF are
declared static and references to fields inside the object, which are prefixed
with BX_PIC_THIS, will use the globally visible object, thePic->. If we don't
use static methods, BX_PIC_SMF evaluates to nothing and BX_PIC_THIS becomes this->.
Making it evaluate to nothing would be a lot cleaner, but then the scoping rules
would change slightly between the two Bochs configurations, which would be a load
of bugs just waiting to happen. Some classes use BX_SMF, others have their own
version of the macro, like BX_PIC_SMF above.
</para>
</section>
<section id="cpu-mem-objects"><title>CPU und memory objects in UP/SMP configurations</title>
<para>
The CPU class is a special case of the above: if Bochs is simulating a uni-
processor machine then there is obviously only one bx_cpu_c object and the
static methods trick can be used. If, on the other hand, Bochs is simulating an
smp machine then we can't use the trick. The same seems to be true for memory:
for some reason, we have a memory object for each CPU object. This might become
relevant for NUMA machines, but they are not all that common -- and even the
existing IA-32 NUMA machines bend over backwards to hide that fact: it should
only be visible in slightly worse timing for non-local memory and non-local
peripherals. Other than that, the memory map and device map presented to each
CPU will be identical.
</para>
<para>
In a UP configuration, the CPU object is declared as bx_cpu. In an SMP
configuration it will be an array of pointers to CPU objects (bx_cpu_array[]).
For memory that would be bx_mem and bx_mem_array[], respectively.
Each CPU object contains a pointer to its associated memory object.
Access of a CPU object often goes through the BX_CPU(x) macro, which either
ignores the parameter and evaluates to &amp;bx_cpu, or evaluates to bx_cpu_array
[n], so the result will always be a pointer. The same goes for BX_MEM(x).
If static methods are used then BX_CPU_THIS_PTR evaluates to BX_CPU(0)->. Ugly,
isn't it?
</para>
</section>
<section id="config-parameter-tree"><title>The configuration parameter tree</title>
<para>
Starting with version 1.3, the Bochs configuration parameters are stored in parameter
objects. These objects have get/set methods with min/max checks and it is possible
to define parameter handlers to perform side effects and to override settings.
Each parameter type has it's own object type with specific features (numeric,
boolean, enum, string and file name). A special object type containing a list of
parameters is designed for building and managing configuration menus or dialogs
automatically. In the original implementation the parameters could be accessed
only with their unique id from a static list or a special structure containing
pointers to all parameters.
</para>
<para>
Starting with version 2.3, the Bochs parameter object handling has been rewritten
to a parameter tree. There is now a root list containing child lists, and these
lists can contain lists or parameters and so on. The parameters are now accessed
by a name build from all the list names in the path and finally the parameter
name separated by periods.
<screen>
Bit32u megs = SIM->get_param_num("memory.standard.ram.size")->get();
</screen>
</para>
<para>
The example above shows how to get the memory size in megabytes from the simulator
interface. In the root list (".") there is child list named "memory" containing
a child list "standard". It's child list "ram" contains the numeric parameter type
"size". The SIM->get_param_num() methods returns the object pointer and the get()
method returns the parameter value.
</para>
<para>
The table below shows all parameter types used by the Bochs configuration interface.
<table>
<title>Parameter types</title>
<tgroup cols="2">
<thead>
<row>
<entry>Type</entry>
<entry>Description</entry>
</row>
</thead>
<tbody>
<row>
<entry>bx_object_c</entry>
<entry>Base class for all the other parameter types. It contains the unique parameter id and the object type value.</entry>
</row>
<row>
<entry>bx_param_c</entry>
<entry>Generic parameter class. It contains the name, label, description and the input/output formats.</entry>
</row>
<row>
<entry>bx_param_num_c</entry>
<entry>Numerical (decimal/hex) config settings are stored in this parameter type.</entry>
</row>
<row>
<entry>bx_param_bool_c</entry>
<entry>This parameter type is based on bx_param_num_c, but it is designed for boolean values. A dependency
list can be defined to enable/disable other parameters depending on the value change.</entry>
</row>
<row>
<entry>bx_param_enum_c</entry>
<entry>Based on bx_param_num_c this parameter type contains a list of valid values.</entry>
</row>
<row>
<entry>bx_param_string_c</entry>
<entry>Configuration strings are stored in this type of parameter.</entry>
</row>
<row>
<entry>bx_param_filename_c</entry>
<entry>Based on bx_param_string_c this parameter type is used for file names.</entry>
</row>
<row>
<entry>bx_list_c</entry>
<entry>Contains a list of pointers to parameters (bx_param_*_c and bx_list_c).
In the config interface it is used for menus/dialogs.</entry>
</row>
</tbody>
</tgroup>
</table>
</para>
</section>
<section id="save-restore"><title>The save/restore feature</title>
<para>
The save/restore feature is based on an extension to the parameter tree concept.
A subtree (list) called "bochs" appears in the root of the parameter tree
and some new "shadow" parameter types store pointers to values instead of the values
itself. All the hardware objects have register_state() methods to register pointers
to the device registers and switches that need to be saved. The simulator interface
saves the registered data in text format to the specified folder (usually one file
per item in the save/restore list). Large binary arrays are registered with a
special parameter type, so they are saved as separate files. The filename is then
created from the full parameter path without the prefix "bochs.".
</para>
<para>
The table below shows the additional parameter types for save/restore.
<table>
<title>Save/restore parameter types</title>
<tgroup cols="2">
<thead>
<row>
<entry>Type</entry>
<entry>Description</entry>
</row>
</thead>
<tbody>
<row>
<entry>bx_shadow_num_c</entry>
<entry>Based on bx_param_num_c this type stores a pointer to a numerical variable.</entry>
</row>
<row>
<entry>bx_shadow_bool_c</entry>
<entry>This parameter type stores a pointer to a boolean variable (using bit #0
of a numerical one).</entry>
</row>
<row>
<entry>bx_shadow_data_c</entry>
<entry>This special parameter type stores pointer size of a binary array. The data is
saved in a separate file and the text file uses the file name as the value.</entry>
</row>
<row>
<entry>bx_shadow_filedata_c</entry>
<entry>This special parameter type stores the descriptor of an open file
(added in Bochs 2.5).</entry>
</row>
</tbody>
</tgroup>
</table>
</para>
<para>
It is also possible to use the bx_param_num_c object with parameter save/restore
handlers. With this special way several device settings can be save to and restored
from one single parameter. The disk image state is also handled this way (see below).
</para>
<para>
All devices can uses these two save/restore specific methods:
<itemizedlist>
<listitem><para>register_state() is called after the device init() to register the device members for save/restore</para></listitem>
<listitem><para>after_restore_state() is an optional method to do things directly after restore (e.g. force a display update)</para></listitem>
</itemizedlist>
</para>
<para>
To implement save/restore for hard drive images, the new method register_state() has
been added to the base class of the disk image objects. It creates a bx_param_bool_c
object called "image" and installs static save and restore handlers. The save
operation finally sets the parameter's value (1 = success) and the save/restore
handlers are doing the main job. The static handlers call the class-specific code.
Depending on the image "mode" they copy either the whole image file or the file
containing changes (journal). The files are saved similar to binary arrays with
the same naming convention. The restore methods are doing some format or coherency
checks, close the open image, copy the file(s) and finally re-open the image.
</para>
</section>
</section>

     <section id="configure-scripting"><title>Configure Scripting</title>
      <para>
      &FIXME;
      configure script, makefiles, header files
      </para>
     </section>

<section id="logfunctions"><title>Log Functions</title>
<para>
The <emphasis>logfunctions</emphasis> class is one of the base classes of Bochs.
It supports 4 log levels (debug, info, error, panic) and 4 possible "actions"
that can be done when a log event occurs. Most of the higher level C++ classes of Bochs
inherit this class to make the logging configuration per object (here called "module")
possible. In the Bochs sources the log events appear as macros (BX_DEBUG, BX_INFO,
BX_ERROR, BX_PANIC) and they call the related logfunction methods, unless the
symbol BX_NO_LOGGING is set to 1. This is the definition in <emphasis>bochs.h</emphasis>:
<screen>
typedef class BOCHSAPI logfunctions
{
  char *name;
  char *prefix;
  int onoff[N_LOGLEV];
  class iofunctions *logio;
  // default log actions for all devices, declared and initialized
  // in logio.cc.
  BOCHSAPI_CYGONLY static int default_onoff[N_LOGLEV];
public:
  logfunctions(void);
  logfunctions(class iofunctions *);
 ~logfunctions(void);

  void info(const char *fmt, ...)   BX_CPP_AttrPrintf(2, 3);
  void error(const char *fmt, ...)  BX_CPP_AttrPrintf(2, 3);
  void panic(const char *fmt, ...)  BX_CPP_AttrPrintf(2, 3);
  void ldebug(const char *fmt, ...) BX_CPP_AttrPrintf(2, 3);
  void fatal (const char *prefix, const char *fmt, va_list ap, int exit_status);
  void ask (int level, const char *prefix, const char *fmt, va_list ap);
  void put(const char *p);
  void put(const char *n, const char *p);
  void setio(class iofunctions *);
  void setonoff(int loglev, int value) {
    assert (loglev >= 0 && loglev < N_LOGLEV);
    onoff[loglev] = value;
  }
  const char *get_name() const { return name; }
  const char *getprefix() const { return prefix; }
  int getonoff(int level) const {
    assert (level>=0 && level&lt;N_LOGLEV);
    return onoff[level];
  }
  static void set_default_action(int loglev, int action) {
    assert (loglev >= 0 && loglev &lt; N_LOGLEV);
    assert (action >= 0 && action &lt; N_ACT);
    default_onoff[loglev] = action;
  }
  static int get_default_action(int loglev) {
    assert (loglev >= 0 && loglev &lt; N_LOGLEV);
    return default_onoff[loglev];
  }
} logfunc_t;
</screen>
</para>
<section><title>Methods</title>
<para>
Here is a short description of some <emphasis>logfunctions</emphasis> methods.
<itemizedlist>
<listitem><para>
The <emphasis>constructor</emphasis> registers a new log module with default values.
The module's log prefix is empty and the log levels are set up with default actions.
</para></listitem>

<listitem><para>
The <emphasis>destructor</emphasis> removes the log module from the table.
</para></listitem>

<listitem><para>
The <emphasis>info()</emphasis>, <emphasis>error()</emphasis>, <emphasis>panic()</emphasis>
and <emphasis>ldebug()</emphasis> methods are called via macros to create a log event
of the related level.
</para></listitem>

<listitem><para>
The <emphasis>fatal()</emphasis> method is called if a log event occurs and it's
action is set to "fatal". It is used to shut down the Bochs simulation.
</para></listitem>

<listitem><para>
The <emphasis>ask()</emphasis> method is called if a log event occurs and it's
action is set to "ask". It sends an event to the simulator interface and depending
on the return value the simulation continues or it is terminated by calling
<emphasis>fatal()</emphasis>. The simulator interface either prompts the user on
the console or calls some platform / gui specific code to handle the
<emphasis>ask</emphasis> request.
</para></listitem>

<listitem><para>
The <emphasis>put()</emphasis> methods are used to set up the log module prefix in
that appears in the log file and the log module name that appears in the config
interface. If the name is not specified, the prefix is used instead.
</para></listitem>
</itemizedlist>
</para>
<para>
&FIXME; To be continued.
</para>
</section>
</section>

      <section id="timers"><title>timers</title>
      <para>
      &FIXME;
      </para>
      </section>

<section id="cmos-map"><title>Bochs's CMOS map</title>
<para>
In addition to the default CMOS RAM layout, the Bochs BIOS uses some additional
registers for harddisk parameters and the boot sequence. The following table
shows all CMOS registers and their meaning.
</para>
<para>
<screen>
Legend:
S	- set by the emulator (Bochs)
Q	- set by the emulator (Qemu)
B	- set by the bios
U	- unused by the bios

LOC	NOTES	MEANING
0x00	S	rtc seconds
0x01	B	second alarm
0x02	S	rtc minutes
0x03	B	minute alarm
0x04	S	rtc hours
0x05	B	hour alarm

0x06	S,U	day of week
0x07	S,B	date of month
0x08	S,B	month
0x09	S,B	year

0x0a	S,B	status register A
0x0b	S,B	status register B
0x0c	S	status register C
0x0d	S	status register D

0x0f	S	shutdown status
    values:
	0x00: normal startup
	0x09: normal
	0x0d+: normal
	0x05: eoi ?
	else: unimpl

0x10	S	fd drive type (2 nibbles: high=fd0, low=fd1)
    values:
	1: 360K 5.25"
	2: 1.2MB 5.25"
	3: 720K 3.5"
	4: 1.44MB 3.5"
	5: 2.88MB 3.5"

!0x11	configuration bits!!

0x12	S	how many disks first (hd type)

!0x13	advanced configuration bits!!

0x14	S,U	equipment byte (?)
	bits	where		what
	7-6	floppy.cc
	5-4	vga.cc		0 = vga
	2	keyboard.cc	1 = enabled
	0	floppy.cc

0x15	S,U	base memory - low
0x16	S,U	base memory - high

0x17	S,U	extended memory in k - low
0x18	S,U	extended memory in k - high

0x19	S	hd0: extended type
0x1a	S	hd1: extended type

0x1b	S,U	hd0:cylinders - low
0x1c	S,U	hd0:cylinders - high
0x1d	S,U	hd0:heads
0x1e	S,U	hd0:write pre-comp - low
0x1f	S,U	hd0:write pre-comp - high
0x20	S,U	hd0:retries/bad_map/heads>8
0x21	S,U	hd0:landing zone - low
0x22	S,U	hd0:landing zone - high
0x23	S,U	hd0:sectors per track

0x24	S,U	hd1:cylinders - low
0x25	S,U	hd1:cylinders - high
0x26	S,U	hd1:heads
0x27	S,U	hd1:write pre-comp - low
0x28	S,U	hd1:write pre-comp - high
0x29	S,U	hd1:retries/bad_map/heads>8
0x2a	S,U	hd1:landing zone - low
0x2b	S,U	hd1:landing zone - high
0x2c	S,U	hd1:sectors per track

0x2d	S	boot from (bit5: 0:hd, 1:fd)

0x2e	S,U	standard cmos checksum (0x10->0x2d) - high
0x2f	S,U	standard cmos checksum (0x10->0x2d) - low

0x30	S	extended memory in k - low
0x31	S	extended memory in k - high

0x32	S	rtc century

0x34	S	extended memory in 64k - low
0x35	S	extended memory in 64k - high

0x37	S	ps/2 rtc century (copy of 0x32, needed for winxp)

0x38	S	eltorito boot sequence + boot signature check
	bits
	0	floppy boot signature check (1: disabled, 0: enabled)
	7-4	boot drive #3 (0: unused, 1: fd, 2: hd, 3:cd, else: fd)

0x39	S	ata translation policy - ata0 + ata1
	bits
	1-0	ata0-master (0: none, 1: LBA, 2: LARGE, 3: R-ECHS)
	3-2	ata0-slave
	5-4	ata1-master
	7-6	ata1-slave

0x3a	S	ata translation policy - ata2 + ata3 (see above)

0x3d	S	eltorito boot sequence (see above)
	bits
	3-0	boot drive #1
	7-4	boot drive #2
0x5b	S 	extra memory above 4GB
0x5c	S 	extra memory above 4GB
0x5d	S 	extra memory above 4GB
0x5f	Q	number of processors
</screen>
</para>
</section>

<section id="sb16-emulation-basics"> <!-- start of SB16 section-->

<title>Sound Blaster 16 Emulation</title>

<para>
This section is a detailed description for configuring Sound Blaster 16 from
source. If you have a binary and all you want to know is what to put in your
<filename>bochsrc</filename> file, see the <ulink url="../user/bochsrc.html#BOCHSOPT-SB16">sb16</ulink>
bochsrc option in the user guide.
</para>

<para>
The original version of the Sound Blaster 16 (SB16) emulation for Bochs was
written and donated by Josef Drexler. The entire set of his SB16 patches have
been integrated into Bochs, however, so you can find everything you need here.
</para>

<section><title>How well does it work?</title>
<para>
Right now, MPU401 emulation is next to perfect. It supports UART
and SBMIDI mode, because the SB16's MPU401 ports can't do anything else as well.
</para>

<para>
The digital audio basically works, but the emulation is too slow for fluent
output unless the application doesn't do much in the background (or the
foreground, really). The sound tends to looping or crackle on slower
computer, but the emulation appears to be correct. Even a MOD
player works, although only for lower sampling speeds.
</para>
<para>
Also, the MIDI data running through the MPU401 ports can be written
into a SMF, that is the standard midi file. The wave output
can be written into a VOC file, which has a format defined by
Creative Labs. This file format can be converted to WAV by
sox for example.
</para>
</section>

<section><title>Output to a sound card</title>

<para>
Output to the host sound system is supported on Windows, Linux, FreeBSD, MacOS 9,
MacOSX and platforms supported by SDL.
</para>
<para>
On Linux, the output goes to any file or device. If you have a wavetable synthesizer,
midi can go to <filename class="devicefile">/dev/midi00</filename>, otherwise you may need
a midi interpreter. For example, the midid program from the DosEmu project would work.
Wave output should go to <filename class="devicefile">/dev/dsp</filename>. These devices
are assumed to be OSS devices, if they're not some of the ioctl's might fail.
If ALSA is present on Linux and the sound driver is set to <filename>alsa</filename>,
Bochs uses it's default PCM output device and MIDI sequencer.
</para>
<para>
On Windows, midi and (wave) output go to the midi mapper and the wave mapper,
respectively. A future version might have selectable output devices.
</para>
<para>
See the next section for more information about the sound lowlevel interface.
</para>
</section>

<section><title>Configuring Bochs</title>

<para>
You need to <command>configure</command> Bochs using the <option>--enable-sb16</option>
option.
There are a few values in <filename>config.h</filename> that are relevant to the
sound functions. Editing <filename>config.h</filename> after running configure
is usually not necessary, since it detects the available drivers and enables them
for the compilation.
</para>

<para>
BX_USE_SB16_SMF should be 1 unless you intend to have several sound cards
running at the same time.
</para>

<para>
BX_SOUND_LOWLEVEL_C is the name of the class used as the "default" sound driver for
output.  The default value of this setting is the dummy driver with no output. The
configure script usually changes this value. The following are supported at the
moment:
</para>

<programlisting>
        bx_sound_linux_c    for output to /dev/dsp and /dev/midi00 on Linux,
                            FreeBSD and maybe other OSes that use the OSS driver.
        bx_sound_windows_c  for output to the midi and wave mapper of
                            Windows 3.1 and higher.
        bx_sound_alsa_c     for output to the default ALSA PCM device and the
                            default ALSA sequencer.
        bx_sound_osx_c      for output on Mac OS 9 and Mac OSX.
        bx_sound_sdl_c      for wave output on platforms supported by SDL.
        bx_sound_output_c   for no output at all.
</programlisting>

<para>
Setup the SB16 emulation in your <filename>bochsrc</filename>, according to instructions
in that file (see <ulink url="../user/bochsrc.html#BOCHSOPT-SB16">sb16</ulink> option
in the user guide).
</para>
</section>

<section><title>Runtime configuration</title>

<para>
The source and the DOS executable for the SB16CTRL program that is used to modify
the runtime behaviour of the SB16 emulator is included in
misc/sb16.
</para>

<para>
See the section <ulink url="../user/using-sound.html#SB16CTRL">SB16CTRL</ulink>
in the user documentation for information about the commands of SB16CTRL.
</para>
</section>

</section> <!-- end of SB16 section-->

<section id="sound-lowlovel-basics">
<title>The sound lowlevel interface</title>

<para>
This file is intended for programmers who would like to port the sound
output routines to their platform. It gives a short outline what services
have to be provided.
</para>
<para>
You should also have a look at the exisiting files, <emphasis>SOUNDMOD.CC</emphasis>
and e.g. <emphasis>SOUNDLNX.CC</emphasis> for Linux or <emphasis>SOUNDWIN.CC</emphasis>
for Windows and their respective header files to get an idea about how these things
really work.
</para>

<section><title>Files</title>

<para>
The main include file for a lowlevel sound driver is <emphasis>iodev.h</emphasis>.
It has all definitions for the system-independent functions that a sound driver
uses. The sound driver also needs to include <emphasis>soundmod.h</emphasis> for
the definition of the base class <emphasis>bx_sound_output_c</emphasis>.
</para>

<para>
Additionally, every output driver will have an include file, which should be
included on top of <filename>soundmod.cc</filename> to allow the emulator
to use that driver. A soundcard does not need to include the specific driver
header.
</para>

<para>
To actually make the emulator use any specific driver as the default,
<emphasis>BX_SOUND_LOWLEVEL_C</emphasis> has to be set to the name of the
respective output class.
</para>

<para>
Note that if your class contains any system-specific statements,
include-files and so on, you should enclose both the include-file and
the CC-file in an <emphasis>#if defined</emphasis> (OS-define) construct.
Also don't forget to add your file to the list of lowlevel sound object
files (<emphasis>SOUNDLOW_OBJS</emphasis>) in the file <emphasis>configure.in</emphasis>
and to regenerate the configure script,
</para>
</section>

<section><title>Classes</title>

<para>
The following classes are involved with the sound lowlevel interface:
</para>
<itemizedlist>
<listitem><para>
<emphasis>bx_soundmod_ctl_c</emphasis> is a pseudo device that is used to
initialize the sound driver depending on the configuration. In addition to
this, it has methods for the PC speaker beep generation and the VOC file
output.
</para></listitem>

<listitem><para>
<emphasis>bx_sound_output_c</emphasis> is the base output class. It has all
the methods used by the soundcard emulation, but only as stubs and does not
actually produce any output. These methods are then called by
the emulator whenever output is necessary.
</para></listitem>

<listitem><para>
<emphasis>bx_sound_OS_c</emphasis> is derived from
<emphasis>bx_sound_output_c</emphasis>. It contains the code to generate
output for the <emphasis>OS</emphasis> operating system.
It is not necessary to override all the methods defined in the base class, since
virtual functions are used. The constructor should call the inherited constructor
as usual, even though the current constructor does not do anything yet.
</para></listitem>
</itemizedlist>
</section>

<section><title>The base class <emphasis>bx_sound_output_c</emphasis></title>
<para>
<screen>
class bx_sound_lowlevel_c : public logfunctions {
public:

  bx_sound_lowlevel_c();
  virtual ~bx_sound_lowlevel_c();

  virtual int get_type() {return BX_SOUNDLOW_DUMMY;}

  virtual int waveready();
  virtual int midiready();

  virtual int openmidioutput(const char *mididev);
  virtual int sendmidicommand(int delta, int command, int length, Bit8u data[]);
  virtual int closemidioutput();

  virtual int openwaveoutput(const char *wavedev);
  virtual int startwaveplayback(int frequency, int bits, bx_bool stereo, int format);
  virtual int sendwavepacket(int length, Bit8u data[]);
  virtual int stopwaveplayback();
  virtual int closewaveoutput();

  virtual int openwaveinput(const char *wavedev, sound_record_handler_t rh);
  virtual int startwaverecord(int frequency, int bits, bx_bool stereo, int format);
  virtual int getwavepacket(int length, Bit8u data[]);
  virtual int stopwaverecord();
  virtual int closewaveinput();

  static void record_timer_handler(void *);
  void record_timer(void);
protected:
  int record_timer_index;
  int record_packet_size;
  sound_record_handler_t record_handler;
};
</screen>
The base class for sound lowlevel support is derived from the <emphasis>logfunctions</emphasis>
class to make the Bochs logging capabilities available in the sound driver code.
It contains the framework for wave input (recording) support. The base class is
in use if the "dummy" sound driver is selected or in case no platform or library
specific implementation is available.
</para>
</section>

<section><title>Methods</title>
<para>
The following are the methods that the sound driver class has to override.
All but constructor and destructor have to return either
<emphasis>BX_SOUNDLOW_OK</emphasis> <emphasis>(0)</emphasis> if the function
was successful, or <emphasis>BX_SOUNDLOW_ERR</emphasis> <emphasis>(1)</emphasis>
if not. If any of the initialization functions fail, output to that device is
disabled until the emulator is restarted.
</para>

<section><title>bx_sound_OS_c()</title>

<para>
The emulator instantiates the class at the initialization of Bochs.
</para>

<para>
The constructor should <emphasis>not</emphasis> allocate the output devices.
This shouldn't be done until the actual output occurs; in either
<emphasis>openmidioutput()</emphasis> or <emphasis>openwaveoutput()</emphasis>.
Otherwise it would be impossible to have two copies of Bochs running
concurrently (if anybody ever wants to do this).
</para>
</section>

<section><title>~bx_sound_OS_c()</title>

<para>
The instance is destroyed just before Bochs ends.
</para>
</section>

<section><title>int get_type()</title>
<para>
Returns.the ID of the sound driver module. The default value is <emphasis>BX_SOUNDLOW_DUMMY</emphasis>.
New values should be added to the list in <emphasis>soundmod.h</emphasis>.
</para>
</section>

<section><title>int openmidioutput(char *device)</title>

<itemizedlist>
<listitem><para>
<emphasis>openmidioutput()</emphasis> is called when the first midi output starts.
It is only called if the midi output to the driver is active (midimode 1). It should
prepare the given MIDI hardware for receiving midi commands.
</para></listitem>
</itemizedlist>

<para>
Description of the parameters:
</para>

<para>
<itemizedlist>

<listitem><para>
<emphasis>device</emphasis> is a system-dependent variable.
It contains the value of the <emphasis>MIDI=device</emphasis> configuration option.
</para></listitem>

<listitem><para>
Note that only one midi output device will be used at any one time.
<emphasis>device</emphasis>
may not have the same value throughout one session, but it will be closed
before it is changed.
</para></listitem>
</itemizedlist>
</para>
</section>

<section><title>int midiready()</title>

<para>
<emphasis>midiready()</emphasis> is called whenever the applications asks if the
midi queue can accept more data.
</para>

<para>
Return values:
</para>

<itemizedlist>
<listitem><para>
<emphasis>BX_SOUNDLOW_OK</emphasis> if the midi output device is ready.
</para></listitem>

<listitem><para>
<emphasis>BX_SOUNDLOW_ERR</emphasis> if it isn't ready.
</para></listitem>
</itemizedlist>

<para>
<emphasis>Note: </emphasis><emphasis>midiready()</emphasis> will be called a few times
<emphasis>before</emphasis> the device is opened. If this is the case, it should
always report that it is ready, otherwise the application (not Bochs)
will hang.
</para>
</section>

<section><title>int sendmidicommand(int delta, int command, int length, Bit8u data[])</title>

<para>
<emphasis>sendmidicommand()</emphasis>is called whenever a complete midi command has
been written to the emulator. It should then send the given midi command to the midi hardware.
It will only be called after the midi output has been opened. Note that
if at all possible it should not wait for the completion of the command
and instead indicate that the device is not ready during the execution
of the command. This is to avoid delays in the program while it is
generating midi output.
</para>

<para>
Description of the parameters:
</para>

<itemizedlist>
<listitem><para>
<emphasis>delta</emphasis> is the number of delta ticks that
have passed since the last command has been issued. It is always zero for
the first command. There are 24 delta ticks per quarter, and 120 quarters
per minute, thus 48 delta ticks per second.
</para></listitem>

<listitem><para>
<emphasis>command</emphasis> is the midi command byte (sometimes
called status byte), in the usual range of 0x80..0xff. For more information
please see the midi standard specification.
</para></listitem>

<listitem><para>
<emphasis>length</emphasis> is the number of data bytes that
are contained in the data structure. This does <emphasis>not</emphasis> include the status
byte which is not replicated in the data array. It can only be greater
than 3 for SysEx messages (commands <emphasis>0xF0</emphasis> and <emphasis>0xF7</emphasis>)
</para></listitem>

<listitem><para>
<emphasis>data[]</emphasis> is the array of these data bytes,
in the order they have in the standard MIDI specification.
Note, it might be <emphasis>NULL</emphasis> if length==0.
</para></listitem>
</itemizedlist>
</section>


<section><title>int closemidioutput()</title>

<para>
<emphasis>closemidioutput()</emphasis> is called before shutting down Bochs or
when the
emulator gets the <emphasis>stop_output</emphasis> command through the emulator port.
After this, no more output will be necessary until <emphasis>openmidioutput()</emphasis>
is called again, but <emphasis>midiready()</emphasis> might still be called. It should do the following:
</para>

<itemizedlist>
<listitem><para>
Wait for all remaining messages to be completed
</para></listitem>
<listitem><para>
Reset and close the midi output device
</para></listitem>
</itemizedlist>
</section>


<section><title>int openwaveoutput(char *device)</title>

<para>
<emphasis>openwaveoutput()</emphasis> is called when the sound subsystem
initializes. It should do the following:
</para>

<itemizedlist>
<listitem><para>
Open the given device, and prepare it for wave output
</para></listitem>
</itemizedlist>
<para>
<emphasis>or</emphasis>
</para>
<itemizedlist>
<listitem><para>
Store the device name so that the device can be opened in <emphasis>startwaveplayback()</emphasis>.
</para></listitem>
</itemizedlist>

<para>
<emphasis>openwaveoutput()</emphasis> will only be called once, whereas
<emphasis>startwaveplayback()</emphasis> is called for every new wave output
command to the soundcard emulation. If feasible, it could be useful to open
and/or lock  the output device in <emphasis>startwaveplayback()</emphasis> as
opposed to <emphasis>openwaveoutput()</emphasis> to ensure that it can be used
by other applications while Bochs doesn't need it.
</para>

<para>
However, many older applications don't use the auto-init DMA
mode, which means that they start a new DMA transfer for every single
block of output, which means usually for every 2048 bytes or so.
Unfortunately there is no way of knowing whether the application will
restart an expired DMA transfer soon, so that in these cases the
<emphasis>startwaveplayback</emphasis> function will be called very often, and it
isn't a good idea to have it reopen the device every time.
</para>

<para>The buffer when writing to the device should not be overly large.
Usually about four buffers of 4096 bytes produce best results. Smaller
buffers could mean too much overhead, while larger buffers contribute
to the fact that the actual output will always be late when the application
tries to synchronize it with for example graphics.
</para>

<para>The parameters are the following: </para>

<itemizedlist>
<listitem><para>
<emphasis>device</emphasis> is the wave device selected by the user. It is
strictly system-dependent. The value is that of the <emphasis>waveout=device</emphasis>
configuration parameter of the <emphasis>sound</emphasis> bochsrc option.
</para></listitem>
</itemizedlist>

<para>
Note that only one wave output device will be used at any one time.
<emphasis>device</emphasis> may not have the same value throughout one session,
but it will be closed before it is changed.
</para>
</section>

<section>
<title>int startwaveplayback(int frequency, int bits, int stereo, int format)</title>

<para>
This function is called whenever the emulator receives a new wave output command.
It should do the following:
</para>

<itemizedlist>
<listitem><para>
Open the wave output device, unless <emphasis>openwaveoutput()</emphasis> did that
already
</para></listitem>

<listitem><para>
Prepare the device for data and set the device parameters to those given
in the function call
</para></listitem>
</itemizedlist>

<para>
The parameters are the following:
</para>

<itemizedlist>
<listitem><para>
<emphasis>frequency</emphasis> is the desired frequency of the
output. Because of the capabities of the soundcards, it can have any value
between 5000 and 44,100.
</para></listitem>

<listitem><para>
<emphasis>bits</emphasis> is either 8 or 16, denoting the resolution
of one sample.
</para></listitem>

<listitem><para>
<emphasis>stereo</emphasis> is either 1 for stereo output, or 0 for mono output.
</para></listitem>

<listitem><para>
<emphasis>format</emphasis> is a bit-coded value (see below).
</para></listitem>
</itemizedlist>

<para>
<table>
<title>format bits</title>
<tgroup cols="2">
<thead>
<row>
<entry>Bit number</entry>
<entry>Meaning</entry>
</row>
</thead>
<tbody>
<row> <entry> 0 (LSB)  </entry><entry><para> 0: unsigned data </para><para>
                                            1: signed data </para></entry> </row>
<row> <entry> 1..6     </entry><entry> Type of codec (see below) </entry> </row>
<row> <entry> 7        </entry><entry><para> 0: no reference byte </para><para>
                                             1: with reference byte </para></entry> </row>
<row> <entry> 8..x     </entry><entry> reserved (0) </entry> </row>
</tbody>
</tgroup>
</table>

<table>
<title>codecs</title>
<tgroup cols="2">
<thead>
<row>
<entry>Value</entry>
<entry>Meaning</entry>
</row>
</thead>
<tbody>
<row> <entry> 0 </entry><entry> PCM (raw data) </entry> </row>
<row> <entry> 1 </entry><entry> reserved </entry> </row>
<row> <entry> 2 </entry><entry> 2-bit ADPCM (Creative Labs format) </entry> </row>
<row> <entry> 3 </entry><entry> 2.4-bit (3-bit) ADPCM (Creative Labs format) </entry> </row>
<row> <entry> 4 </entry><entry> 4-bit ADPCM (Creative Labs format) </entry> </row>
</tbody>
</tgroup>
</table>
</para>
<para>
Other codecs are not supported by the SB hardware. In fact, most applications will
translate their data into raw data, so that in most cases the codec will be zero.
</para>
<para>
The number of bytes per sample can be calculated from this as (bits / 8) * (stereo + 1).
</para>
</section>


<section>
<title>int waveready()</title>

<para>
This is called whenever the emulator has another output buffer ready
and would like to pass it to the output class. This happens every
<emphasis>BX_SOUNDLOW_WAVEPACKETSIZE</emphasis> bytes, or whenever a DMA transfer
is done or aborted.
</para>

<para>
It should return whether the output device is ready for another buffer
of <emphasis>BX_SOUNDLOW_WAVEPACKETSIZE</emphasis> bytes.
If <emphasis>BX_SOUNDLOW_ERR</emphasis>
is returned, the emulator waits about 1/(frequency * bytes per sample) seconds
and then asks again. The DMA transfer is stalled during that time, but
the application keeps running, until the output device becomes ready.
</para>

<para>
As opposed to <emphasis>midiready(), waveready()</emphasis> will <emphasis>not</emphasis> be
called unless the device is open.
</para>
</section>

<section>
<title>int sendwavepacket(int length, Bit8u data[])</title>

<para>
This function is called whenever a data packet of at most
<emphasis>BX_SOUNDLOW_WAVEPACKETSIZE</emphasis> is ready at the soundcard
emulation. It should then do the following:
</para>

<itemizedlist>
<listitem><para>
Send this wave packet to the wave hardware
</para></listitem>
</itemizedlist>

<para>
This function <emphasis>has</emphasis> to be synchronous, meaning that it <emphasis>has</emphasis>
to return immediately, and <emphasis>not</emphasis> wait until the output is done. Also,
this function might be called before the previous output is done. If your
hardware can't append the new output to the old one, you will have to implement
this yourself, or the output will be very chunky, with as much silence
between the blocks as the blocks take to play. This is not what you want.
Instead, <emphasis>waveready()</emphasis> should return <emphasis>BX_SOUND_OUTPUT_ERR</emphasis>
until the device accepts another block of data.
</para>

<para>
Parameters:
</para>

<itemizedlist>
<listitem><para>
<emphasis>length</emphasis> is the number of data bytes in
the data stream. It will never be larger than <emphasis>BX_SOUNDLOW_WAVEPACKETSIZE</emphasis>.
</para></listitem>

<listitem><para>
<emphasis>data</emphasis> is the array of data bytes.
</para></listitem>
</itemizedlist>

<para>
The order of bytes in the data stream is the same as that in the Wave file format:

<table>
<title>wave output types</title>
<tgroup cols="2">
<thead>
<row>
<entry>Output type</entry>
<entry>Sequence of data bytes</entry>
</row>
</thead>
<tbody>
<row> <entry> 8 bit mono </entry><entry> Sample 1; Sample 2; Sample 3; etc. </entry> </row>
<row> <entry> 8 bit stereo </entry><entry> Sample 1, Channel 0; Sample 1, Channel 1; Sample 2, Channel 0; Sample 2, Channel 1; etc. </entry> </row>
<row> <entry> 16 bit mono </entry><entry> Sample 1, LSB; Sample 1, MSB; Sample 2, LSB; Sample 2, MSB; etc. </entry> </row>
<row> <entry> 16 bit stereo </entry><entry> Sample 1, LSB, Channel 0; Sample 1, MSB, Channel 0; Sample 1, LSB, Channel 1; Sample 1, MSB, Channel 1; etc. </entry> </row>
</tbody>
</tgroup>
</table>
</para>

<para>
Typically 8 bit data will be unsigned with values from 0 to 255, and
16 bit data will be signed with values from -32768 to 32767, although the
SB16 is not limited to this. For further information on the codecs and
the use of reference bytes please refer to the Creative Labs Sound Blaster
Programmer's Manual, which can be downloaded from the Creative Labs web
site.
</para>
</section>

<section><title>int stopwaveplayback()</title>

<para>
This function is called at the end of a wave data transfer. It should do the following:
</para>

<itemizedlist>
<listitem><para>
Close the output device if it was opened by <emphasis>startwaveplayback()</emphasis>.
and it's not going to be opened soon. Which is almost impossible to tell.
</para></listitem>
</itemizedlist>
</section>

<section><title>int closewaveoutput()</title>

<para>
This function is called just before Bochs exits. It should do the following:
</para>

<itemizedlist>
<listitem><para>
Close the output device, if this hasn't been done by <emphasis>stopwaveplayback()</emphasis>.
</para></listitem>
</itemizedlist>

<para>
Typically, <emphasis>stopwaveplayback()</emphasis> will be called several times, whenever
a data transfer is done, where <emphasis>closewaveoutput()</emphasis> will only be called
once. However, in the future it might be possible that <emphasis>openwaveoutput()</emphasis>
is called again, for example if the user chose to switch devices while
Bochs was running. This is not supported at the moment, but might be in
the future.
</para>
</section>
</section>

<section><title>Methods and members for wave input (recording) support</title>
<para>
The wave input feature is relatively new in Bochs. If a lowlevel driver does not
implement recording, the methods of the base class ("dummy" driver) are used. They
return silence to let the input mechanism of the soundcard emulation work. The
soundcard emulator object needs to implement a callback function to notifies
the emulation about available data. This function usually calls the driver method
to get the wave data packet. The driver objects has a periodic timer with an
interval of 0.1 emulated seconds that is active during recording. The timer
handler processes the wave data recorded with platform or library specific
function and finally notifies the emulator.
</para>

<section><title>int openwaveinput(char *device, sound_record_handler_t rh)</title>
<para>
<emphasis>openwaveinput()</emphasis> is called when the sound emulation first
receives a sound recording command. It should do the following:
</para>

<itemizedlist>
<listitem><para>
Open the given device, and prepare it for wave input
</para></listitem>
</itemizedlist>
<para>
<emphasis>or</emphasis>
</para>
<itemizedlist>
<listitem><para>
Store the device name so that the device can be opened in <emphasis>startwaverecord()</emphasis>.
</para></listitem>
</itemizedlist>

<para>
In addition to this the record handler value should be stored and the record timer
should be registered.
</para>

<para>
<emphasis>openwaveinput()</emphasis> will only be called once, whereas
<emphasis>startwaverecord()</emphasis> is called for every new wave input
command to the soundcard emulation. If feasible, it could be useful to open
and/or lock  the input device in <emphasis>startwaverecord()</emphasis> as
opposed to <emphasis>openwaveinput()</emphasis> to ensure that it can be used
by other applications while Bochs doesn't need it.
</para>

<para>The parameters are the following: </para>

<itemizedlist>
<listitem><para>
<emphasis>device</emphasis> is the wave device selected by the user. It is
strictly system-dependent. The value is that of the <emphasis>wavein=device</emphasis>
configuration parameter of the <emphasis>sound</emphasis> bochsrc option.
</para></listitem>
<listitem><para>
<emphasis>rh</emphasis> is a pointer to the record handler method of the sound
emulation. When sound recording is active, this handler is called periodicly to
notify the sound emulation about newly available data.
</para></listitem>
</itemizedlist>

<para>
Note that only one wave input device will be used at any one time.
<emphasis>device</emphasis> may not have the same value throughout one session,
but it will be closed before it is changed.
</para>
</section>

<section>
<title>int startwaverecord(int frequency, int bits, int stereo, int format)</title>
<para>
This method is very similar to the <emphasis>startwaveplayback()</emphasis> method for
sound output and it takes the same argument list. It should set up the input device
for recording, calculate the size of the recording packet for 0.1 second and start
the record timer.
</para>

<para>
&FIXME; To be completed.
</para>
</section>

</section>

</section>

<section id="harddisk-redologs"><title>Harddisk Images based on redologs</title>
<para>
This section describes how the three new disk images "undoable", "growing", and "volatile" are
implemented in Bochs 2.1. It also applies to the write support the "vvfat" disk
image mode in Bochs 2.4.6.
</para>
<itemizedlist>
<listitem><para>
undoable -> base r/o file, plus growing, commitable, rollbackable redolog file
</para></listitem>
<listitem><para>
growing  -> growing files, all previously unwritten sectors go to the end of file
</para></listitem>
<listitem><para>
volatile -> base r/o file, plus hidden growing redolog
</para></listitem>
<listitem><para>
vvfat -> virtual VFAT disk created from directory, plus hidden growing redolog
</para></listitem>
</itemizedlist>

<para>
</para>

<section>
<title>
        Description
</title>
<para>
The idea behind volatile and undoable disk images is to have a read-only base
file, associated with one redolog file. In case of vvfat, a directory is
associated with the redolog file.
</para>
<para>
Reading a sector is done from the redolog file if it contains
the sector, or from the base file / vvfat directory otherwise.
</para>
<para>
Sectors written go to the redolog,
so base image files are opened in read only mode in this configuration.
</para>
<para>
The redolog is designed in a way so it starts as a small file
and grows with every new sectors written to it. Previously written
sectors are done in place. Redolog files can not shrink.
</para>
<para>
The redolog is a growing file that can be created on the fly.
</para>
<para>
Now, it turns out that if you only use a redolog without any
base image file, you get a "growing" disk image.
</para>
<para>
So "undoable", "volatile", "growing" and "vvfat" harddisk images classes
are implemented on top of a redolog class.
</para>
</section>

<section>
<title>
        How redologs works ?
</title>

<para>
At the start of a redolog file, there is a header, so Bochs can check whether
a file is consistent.
This header is also checked when the automatic type and size detection is
selected.
</para>
<para>
The generic part of the header contains values like type of image, and
spec version number.
</para>
<para>
The header also has a specific part.
For redologs, the number
of entries of the catalog, the extent, bitmap and disk size are stored.
</para>

<para>
In a redolog, the disk image is divided in a number of equal size "extents".
Each extent is a collection of successive 512-bytes sectors of the disk image,
preceeded by a n*512bytes bitmap.
</para>

<para>
the n*512bytes bitmap defines the presence (data has been written to it)
of a specific sector in the extent, one bit for each sector.
Therefore with a 512bytes bitmap, each extent can hold up to 4k blocks
</para>

<para>
Typically the catalog can have 256k entries.
With a 256k entries catalog and 512bytes bitmaps, the redolog can hold up to 512GiB
</para>

<note>
<para>
All data is stored on images as little-endian values
</para>
</note>
<section>
<title>
        Header
</title>
<para>
At the start of a redolog file, there is a header. This header is designed
to be reusable by other disk image types.
</para>
<para>
The header length is 512 bytes. It contains :
<table>
<title>Generic header description</title>
<tgroup cols="5">
<thead>
<row>
<entry>Start position in bytes</entry>
<entry>Length in bytes</entry>
<entry>Data type</entry>
<entry>Description</entry>
<entry>Possible values</entry>
</row>
</thead>
<tbody>
<row> <entry> 0 </entry> <entry> 32 </entry> <entry> string </entry> <entry> magical value </entry> <entry> Bochs Virtual HD Image </entry> </row>
<row> <entry> 32 </entry> <entry> 16 </entry> <entry> string </entry> <entry> type of file </entry> <entry> Redolog </entry> </row>
<row> <entry> 48 </entry> <entry> 16 </entry> <entry> string </entry> <entry> subtype of file </entry> <entry> Undoable, Volatile, Growing </entry> </row>
<row> <entry> 64 </entry> <entry> 4 </entry> <entry> Bit32u </entry> <entry> version of used specification </entry> <entry> 0x00010000, 0x00020000 </entry> </row>
<row> <entry> 68 </entry> <entry> 4 </entry> <entry> Bit32u </entry> <entry> header size </entry> <entry> 512 </entry> </row>
</tbody>
</tgroup>
</table>
</para>
<para>
The current version of the header is 0x00020000 (2.0) - see below for details.
<table>
<title>Redolog specific header description</title>
<tgroup cols="4">
<thead>
<row>
<entry>Start position in bytes</entry>
<entry>Length in bytes</entry>
<entry>Data type</entry>
<entry>Description</entry>
</row>
</thead>
<tbody>
<row> <entry> 72 </entry> <entry> 4 </entry> <entry> Bit32u </entry> <entry> number of entries in the catalog </entry> </row>
<row> <entry> 76 </entry> <entry> 4 </entry> <entry> Bit32u </entry> <entry> bitmap size in bytes </entry> </row>
<row> <entry> 80 </entry> <entry> 4 </entry> <entry> Bit32u </entry> <entry> extent size in bytes</entry> </row>
<row> <entry> 84 </entry> <entry> 4 </entry> <entry> Bit32u </entry> <entry> timestamp in FAT format ("undoable" mode only - otherwise reserved)</entry> </row>
<row> <entry> 88 </entry> <entry> 8 </entry> <entry> Bit64u </entry> <entry> disk size in bytes </entry> </row>
</tbody>
</tgroup>
</table>
</para>
<para>
The reserved field between "extent" and "disk" has been added in redolog version
2.0 to fix an alignment bug on some platforms. It is now used for consistency
check of the "undoable" mode. When creating the redolog file, the timestamp of
the read-only file is stored there (in FAT format). After that, the "undoable"
mode init code compares the timestamp of the r/o file with the one stored in
the redolog.
</para>
</section>

<section>
<title>
        Catalog
</title>
<para>
Immediately following the header, there is a catalog containing
the position number (in extents) where each extent is located in the file.
</para>
<para>
Each position is a Bit32u entity.
</para>
</section>

<section>
<title>
        Bitmap
</title>
<para>
Each extent starts with a bitmap block of n*512 bytes size. Each byte of the
bitmap stores the write status of 8 coresponding disk sectors in the extent
(1 = data written).
</para>
</section>

<section>
<title>
        Extent
</title>
<para>
This is a collection of successive 512-bytes sectors of the disk image.
The bitmap preceeding this data block contains the write status of each sector.
</para>
</section>
</section>

<section>
<title>Parameters
</title>
<para>
The following tables shows what parameters are used when creating redologs or creating "growing" images :
<table>
<title>
        How number of entries in the catalog and number of blocks by extents are computed
</title>
<tgroup cols="5">
<thead>
<row>
<entry>Catalog entries</entry> <entry>Catalog size(KiB)</entry> <entry>Bitmap size (B)</entry> <entry>Extent size (KiB)</entry> <entry>Disk Max Size</entry>
</row>
</thead>

<tbody>
<row>
<entry>512</entry> <entry>2</entry> <entry>1</entry> <entry>4</entry> <entry>2MiB</entry>
</row>
<row>
<entry>512</entry> <entry>2</entry> <entry>2</entry> <entry>8</entry> <entry>4MiB</entry>
</row>
<row>
<entry>1k</entry> <entry>4</entry> <entry>2</entry> <entry>8</entry> <entry>8MiB</entry>
</row>
<row>
<entry>1k</entry> <entry>4</entry> <entry>4</entry> <entry>16</entry> <entry>16MiB</entry>
</row>
<row>
<entry>2k</entry> <entry>8</entry> <entry>4</entry> <entry>16</entry> <entry>32MiB</entry>
</row>
<row>
<entry>2k</entry> <entry>8</entry> <entry>8</entry> <entry>32</entry> <entry>64MiB</entry>
</row>
<row>
<entry>4k</entry> <entry>16</entry> <entry>8</entry> <entry>32</entry> <entry>128MiB</entry>
</row>
<row>
<entry>4k</entry> <entry>16</entry> <entry>16</entry> <entry>64</entry> <entry>256MiB</entry>
</row>
<row>
<entry>8k</entry> <entry>32</entry> <entry>16</entry> <entry>64</entry> <entry>512MiB</entry>
</row>
<row>
<entry>8k</entry> <entry>32</entry> <entry>32</entry> <entry>128</entry> <entry>1GiB</entry>
</row>
<row>
<entry>16k</entry> <entry>64</entry> <entry>32</entry> <entry>128</entry> <entry>2GiB</entry>
</row>
<row>
<entry>16k</entry> <entry>64</entry> <entry>64</entry> <entry>256</entry> <entry>4GiB</entry>
</row>
<row>
<entry>32k</entry> <entry>128</entry> <entry>64</entry> <entry>256</entry> <entry>8GiB</entry>
</row>
<row>
<entry>32k</entry> <entry>128</entry> <entry>128</entry> <entry>512</entry> <entry>16GiB</entry>
</row>
<row>
<entry>64k</entry> <entry>256</entry> <entry>128</entry> <entry>512</entry> <entry>32GiB</entry>
</row>
<row>
<entry>64k</entry> <entry>256</entry> <entry>256</entry> <entry>1024</entry> <entry>64GiB</entry>
</row>
<row>
<entry>128k</entry> <entry>512</entry> <entry>256</entry> <entry>1024</entry> <entry>128GiB</entry>
</row>
<row>
<entry>128k</entry> <entry>512</entry> <entry>512</entry> <entry>2048</entry> <entry>256GiB</entry>
</row>
<row>
<entry>256k</entry> <entry>1024</entry> <entry>512</entry> <entry>2048</entry> <entry>512GiB</entry>
</row>
<row>
<entry>256k</entry> <entry>1024</entry> <entry>1024</entry> <entry>4096</entry> <entry>1TiB</entry>
</row>
<row>
<entry>512k</entry> <entry>2048</entry> <entry>1024</entry> <entry>4096</entry> <entry>2TiB</entry>
</row>
<row>
<entry>512k</entry> <entry>2048</entry> <entry>2048</entry> <entry>8192</entry> <entry>4TiB</entry>
</row>
<row>
<entry>1024k</entry> <entry>4096</entry> <entry>2048</entry> <entry>8192</entry> <entry>8TiB</entry>
</row>
<row>
<entry>1024k</entry> <entry>4096</entry> <entry>4096</entry> <entry>16384</entry> <entry>16TiB</entry>
</row>
<row>
<entry>2048k</entry> <entry>8192</entry> <entry>4096</entry> <entry>16384</entry> <entry>32TiB</entry>
</row>
</tbody>
</tgroup>
</table>
</para>

</section>

<section>
<title>
        Redolog class description
</title>
<para>
The class <emphasis>redolog_t();</emphasis> implements the necessary
methods to create, open, close, read and write data to a redolog.
It also contains methods for the subtype and consistency check and
for the save/restore support. Managment of header catalog and sector
bitmaps is done internally by the class.
</para>
<section>
<title>
        Constants
</title>
<para>
<screen>
#define STANDARD_HEADER_MAGIC     "Bochs Virtual HD Image"
#define STANDARD_HEADER_VERSION   (0x00020000)
#define STANDARD_HEADER_SIZE      (512)
</screen>
These constants are used in the generic part of the header.
</para>

<para>
<screen>
#define REDOLOG_TYPE "Redolog"
#define REDOLOG_SUBTYPE_UNDOABLE "Undoable"
#define REDOLOG_SUBTYPE_VOLATILE "Volatile"
#define REDOLOG_SUBTYPE_GROWING  "Growing"
</screen>
These constants are used in the specific part of the header.
</para>

<para>
<screen>
#define REDOLOG_PAGE_NOT_ALLOCATED (0xffffffff)
</screen>
This constant is used in the catalog for an unwritten extent.
</para>

</section> <!-- Constants -->

<section> <title>Methods</title>
<para>
<emphasis>redolog_t();</emphasis> instanciates a new redolog.
</para>
<para>
<emphasis>int make_header(const char* type, Bit64u size);</emphasis> creates a header
structure in memory, and sets its <emphasis>type</emphasis> and parameters based on the
disk image <emphasis>size</emphasis>. Returns 0.
</para>
<para>
<emphasis>int create(const char* filename, const char* type, Bit64u size);</emphasis>
creates a new empty redolog file, with header and catalog, named <emphasis>filename</emphasis>
of type <emphasis>type</emphasis> for a <emphasis>size</emphasis> bytes image.
Returns 0 for OK or -1 if a problem occured.
</para>
<para>
<emphasis>int create(int filedes, const char* type, Bit64u size);</emphasis>
creates a new empty redolog file, with header and catalog, in a previously
opened file described by <emphasis>filedes</emphasis>, of type <emphasis>type</emphasis>
for a <emphasis>size</emphasis> bytes image.
Returns 0 for OK or -1 if a problem occured.
</para>
<para>
<emphasis>int open(const char* filename, const char* type, Bit64u size);</emphasis>
opens a redolog file named <emphasis>filename</emphasis>, and checks
for consistency of header values against a <emphasis>type</emphasis> and
<emphasis>size</emphasis>.
Returns 0 for OK or -1 if a problem occured.
</para>
<para>
<emphasis>int open(const char* filename, const char* type, Bit64u size, int flags);</emphasis>
opens a redolog file with <emphasis>flags</emphasis> applied. This allows to
open a redolog in read-only mode. All other parameters and the return value are
similar to the default <emphasis>open()</emphasis> method above.
</para>
<para>
<emphasis>void close();</emphasis>
closes a redolog file.
</para>
<para>
<emphasis>off_t lseek(off_t offset, int whence);</emphasis>
seeks at logical data offset <emphasis>offset</emphasis> in a redolog.
<emphasis>offset</emphasis> must be a multiple of 512.
Only SEEK_SET and SEEK_CUR are supported for <emphasis>whence</emphasis>.
Returns -1 if a problem occured, or the current logical offset in
the redolog.
</para>
<para>
<emphasis>ssize_t read(void* buf, size_t count);</emphasis>
reads <emphasis>count</emphasis> bytes of data of the redolog, from current logical offset,
and copies it into <emphasis>buf</emphasis>.
<emphasis>count</emphasis> must be 512.
Returns the number of bytes read, that can be 0 if the data
has not previously be written to the redolog.
</para>
<para>
<emphasis>ssize_t write(const void* buf, size_t count);</emphasis>
writes <emphasis>count</emphasis> bytes of data from <emphasis>buf</emphasis>
to the redolog, at current logical offset.
<emphasis>count</emphasis> must be 512.
Returns the number of bytes written.
</para>
<para>
<emphasis>Bit64u get_size();</emphasis>
returns the size stored in the "disk" field in the header. This is used for size
autodetection feature ("growing" mode) and the consistency check ("undoable"
mode).
</para>
<para>
<emphasis>Bit32u get_timestamp();</emphasis>
returns the value of the "timestamp" field in the header (only used by the
"undoable" mode).
</para>
<para>
<emphasis>bx_bool set_timestamp(Bit32u timestamp);</emphasis>
writes the <emphasis>timestamp</emphasis> to the header. This is done
by the "undoable" mode init code if <emphasis>get_timestamp()</emphasis> returns
0 or the redolog is newly created.
</para>
<para>
<emphasis>static int check_format(int fd, const char *subtype);</emphasis>
checks the format of the file with descriptor <emphasis>fd</emphasis>. Returns
<emphasis>HDIMAGE_FORMAT_OK</emphasis> if the <emphasis>subtype</emphasis>
matches the requested one. This is used for for the image mode autodetection
feature.
</para>
<para>
<emphasis>bx_bool save_state(const char *backup_fname);</emphasis>
copies the redolog file to a new file <emphasis>backup_fname</emphasis>. This is
used by the hdimage save/restore feature.
</para>
</section>

</section> <!-- Redolog class description -->

<section>
<title>
        Disk image classes description
</title>
<para>
"volatile" and "undoable" disk images are easily implemented
by instanciating a <emphasis>device_image_t</emphasis> object (base image)
and a <emphasis>redolog_t</emphasis> object (redolog).
</para>
<para>
"growing" disk images only instanciates a <emphasis>redolog_t</emphasis> object.
</para>
<para>
Class names are <emphasis>undoable_image_t</emphasis>, <emphasis>volatile_image_t</emphasis>
and <emphasis>growing_image_t</emphasis>.
</para>
<para>
When using these disk images, the underlying data structure and layout
is completely hidden to the caller. Then, all offset and size values are
"logical" values, as if the disk was a flat file.
</para>
<section>
<title>
        Constants
</title>
<para>
<screen>
#define UNDOABLE_REDOLOG_EXTENSION ".redolog"
#define UNDOABLE_REDOLOG_EXTENSION_LENGTH (strlen(UNDOABLE_REDOLOG_EXTENSION))
#define VOLATILE_REDOLOG_EXTENSION ".XXXXXX"
#define VOLATILE_REDOLOG_EXTENSION_LENGTH (strlen(VOLATILE_REDOLOG_EXTENSION))
</screen>
These constants are used when building redolog file names
</para>
</section>

<section>
<title>
        undoable_image_t methods
</title>
<para>
<emphasis>
undoable_image_t(Bit64u size, const char* redolog_name);
</emphasis>
instanciates a new <emphasis>undoable_image_t</emphasis>
object. This disk image logical length is <emphasis>size</emphasis> bytes and
the redolog filename is <emphasis>redolog_name</emphasis>.
</para>

<para>
<emphasis>
int open(const char* pathname);
</emphasis>
opens the disk image <emphasis>pathname</emphasis> in read-only mode,
as an undoable disk image. The image mode of this base image is auto-detected.
All supported disk image modes can be used here. The associated
redolog will be named <emphasis>pathname</emphasis> with a
<emphasis>UNDOABLE_REDOLOG_EXTENSION</emphasis> suffix, unless set in the
constructor. Returns 0 for OK or -1 if a problem occured.
</para>

<para>
<emphasis>
void close();
</emphasis>
closes the base image and its redolog.
</para>

<para>
<emphasis>
off_t lseek(off_t offset, int whence);
</emphasis>
seeks at logical data position <emphasis>offset</emphasis> in
the undoable disk image.
Only SEEK_SET and SEEK_CUR are supported for <emphasis>whence</emphasis>.
Returns -1 if a problem occured, or the current logical
offset in the undoable disk image.
</para>

<para>
<emphasis>
ssize_t read(void* buf, size_t count);
</emphasis>
reads <emphasis>count</emphasis> bytes of data
from the undoable disk image, from current logical offset,
and copies it into <emphasis>buf</emphasis>.
<emphasis>count</emphasis> must be 512.
Returns the number of bytes read.
Data will be read from the redolog if it has
been previously written or from the base image
otherwise.
</para>

<para>
<emphasis>
ssize_t write(const void* buf, size_t count);
</emphasis>
writes <emphasis>count</emphasis> bytes of data from <emphasis>buf</emphasis>
to the undoable disk image, at current logical offset.
<emphasis>count</emphasis> must be 512.
Returns the number of bytes written.
Data will always be written to the redolog.
</para>

<para>
<emphasis>
bx_bool save_state(const char *backup_fname);
</emphasis>
calls the related redolog_t method to save the image state.
</para>

<para>
<emphasis>
void restore_state(const char *backup_fname);
called by the hdimage restore code. Copies the backup file to the original
location and overwrites the existing redolog file.
</emphasis>
</para>
</section>

<section>
<title>
        volatile_image_t methods
</title>
<para>
<emphasis>
volatile_image_t(Bit64u size, const char* redolog_name);
</emphasis>
instanciates a new <emphasis>volatile_image_t</emphasis>
object. This disk image logical length is <emphasis>size</emphasis> bytes and
the redolog filename is <emphasis>redolog_name</emphasis> plus a
random suffix.
</para>

<para>
<emphasis>
int open(const char* pathname);
</emphasis>
opens the disk image <emphasis>pathname</emphasis> in read-only mode,
as a volatile disk image. The image mode is auto-detected. The associated
redolog will be named <emphasis>pathname</emphasis> with a random suffix,
unless set in the constructor. Returns 0 for OK or -1 if a problem occured.
</para>

<para>
<emphasis>
void close();
</emphasis>
closes the base image and its redolog.
The redolog is deleted/lost after close is called.
</para>

<para>
<emphasis>
off_t lseek(off_t offset, int whence);
</emphasis>
seeks at logical data position <emphasis>offset</emphasis> in
the volatile disk image.
Only SEEK_SET and SEEK_CUR are supported for <emphasis>whence</emphasis>.
Returns -1 if a problem occured, or the current logical offset in
the volatile disk image.
</para>

<para>
<emphasis>
ssize_t read(void* buf, size_t count);
</emphasis>
reads <emphasis>count</emphasis> bytes of data
from the volatile disk image, from current logical offset,
and copies it into <emphasis>buf</emphasis>.
<emphasis>count</emphasis> must be 512.
Returns the number of bytes read.
Data will be read from the redolog if it has
been previously written or from the base image
otherwise.
</para>

<para>
<emphasis>
ssize_t write(const void* buf, size_t count);
</emphasis>
writes <emphasis>count</emphasis> bytes of data from <emphasis>buf</emphasis>
to the volatile disk image, at current logical offset.
<emphasis>count</emphasis> must be 512.
Returns the number of bytes written.
Data will always be written to the redolog.
</para>

<para>
<emphasis>
bx_bool save_state(const char *backup_fname);
</emphasis>
calls the related redolog_t method to save the image state.
</para>

<para>
<emphasis>
void restore_state(const char *backup_fname);
called by the hdimage restore code. Copies the backup file to the original
location and overwrites the existing redolog file.
</emphasis>
</para>
</section>

<section>
<title>
        growing_image_t methods
</title>
<para>
<emphasis>
growing_image_t(Bit64u size);
</emphasis>
instanciates a new <emphasis>growing_image_t</emphasis>
object. This disk image logical length is <emphasis>size</emphasis> bytes.
</para>

<para>
<emphasis>
int open(const char* pathname);
</emphasis>
opens the growing disk image <emphasis>pathname</emphasis>,
Returns 0 for OK or -1 if a problem occured.
</para>

<para>
<emphasis>
void close();
</emphasis>
closes the growing disk image.
</para>

<para>
<emphasis>
off_t lseek(off_t offset, int whence);
</emphasis>
seeks at logical data position <emphasis>offset</emphasis> in
the growable disk image.
Only SEEK_SET and SEEK_CUR are supported for <emphasis>whence</emphasis>.
Returns -1 if a problem occured, or the current logical offset in
the grwoing image.
</para>

<para>
<emphasis>
ssize_t read(void* buf, size_t count);
</emphasis>
reads <emphasis>count</emphasis> bytes of data
from the growing disk image, from current logical offset,
and copies it into <emphasis>buf</emphasis>.
<emphasis>count</emphasis> must be 512.
Returns the number of bytes read.
The buffer will be filled with null bytes if data
has not been previously written to the growing image.
</para>

<para>
<emphasis>
ssize_t write(const void* buf, size_t count);
</emphasis>
writes <emphasis>count</emphasis> bytes of data from <emphasis>buf</emphasis>
to the growing disk image, at current logical offset.
<emphasis>count</emphasis> must be 512.
Returns the number of bytes written.
</para>

<para>
<emphasis>
static int check_format(int fd, Bit64u imgsize);
</emphasis>
checks the format of the file with descriptor <emphasis>fd</emphasis>. Returns
<emphasis>HDIMAGE_FORMAT_OK</emphasis> if the file format matches the "growing"
one. This is used for the image mode autodetection feature.
</para>

<para>
<emphasis>
bx_bool save_state(const char *backup_fname);
</emphasis>
calls the related redolog_t method to save the image state.
</para>

<para>
<emphasis>
void restore_state(const char *backup_fname);
called by the hdimage restore code. Copies the backup file to the original
location and overwrites the existing redolog file.
</emphasis>
</para>
</section>

</section>

</section>

<section id="add-keymapping"><title>How to add keymapping in a GUI client</title>
<para>
Christophe Bothamy, wrote the keymapping code for Bochs, provided these
instructions to help developers to add keymapping to a GUI.
</para>

<screen>
Bochs creates a bx_keymap_c object named bx_keymap.
This object allows you to :
  - load the configuration specified keymap file
  - get the translated BX_KEY_* from your GUI key

You have to provide a translation function from string to your Bit32u key
constant. Casting will be necessary if your key constants are not Bit32u typed.
The function must be "static Bit32u (*)(const char *)" typed, and must return
BX_KEYMAP_UNKNOWN if it can not translate the parameter string.

What you have to do is :
  - call once "void loadKeymap(Bit32u (*)(const char*))",
    providing your translation function, to load the keymap
  - call "Bit32u getBXKey(Bit32u)" that returns the BX_KEY_*
    constant, for each key you want to map.

The file gui/x.cc implements this architecture, so you can refer to it
as an example.
</screen>

</section>

</chapter>

<chapter id="debugger"><title>Debugger</title>
      <section><title>compile with debugger support</title>
      <para>
      &FIXME;
      </para>
      </section>
      <section id="debugger-get-started"><title>get started in debugger</title>
      <para>
      &FIXME;
      </para>
      </section>
      <section id="debugger-commands"><title>command reference</title>
      <para>
      &FIXME;
      </para>
      </section>
      <section id="debugger-techniques"><title>techniques</title>
      <para>
      &FIXME;
      </para>
      </section>
<section id="iodebug"><title>I/O Interface to Bochs Debugger</title>
<para>
This device was added by Dave Poirier (eks@void-core.2y.net).
</para>
<para>
Compiling Bochs with iodebug support
<screen>
./configure --enable-iodebug
make
</screen>
Other optional fields may be added to the ./configure line, see Bochs
documentation for all the information. To enable the iodebug plugin at runtime,
it must be loaded with the 'plugin_ctrl' bochsrc option.
</para>

<para>
<screen>
Using the I/O Interface to the debugger

port range:  0x8A00 - 0x8A01

Port 0x8A00 servers as command register. You can use it to enable the i/o interface,
change which data register is active, etc.

Port 0x8A01 is used as data register for the memory monitoring.
</screen>
</para>
<section><title>Commands supported by port 0x8A00</title>
<para>
<screen>

0x8A00

 Used to enable the device. Any I/O to the debug module before this command is sent
 is sent will simply be ignored.


0x8A01

 Selects register 0: Memory monitoring range start address (inclusive)


0x8A02

 Selects register 1: Memory monitoring range end address (exclusive)


0x8A80

 Enable address range memory monitoring as indicated by register 0 and 1 and
 clears both registers


0x8AE0 - Return to Debugger Prompt

 If the debugger is enabled (via --enable-debugger), sending 0x8AE0 to port 0x8A00
 after the device has been enabled will return the Bochs to the debugger prompt.
 Basically the same as doing CTRL+C.


0x8AE2 - Instruction Trace Disable

 If the debugger is enabled (via --enable-debugger), sending 0x8AE2 to port 0x8A00
 after the device has been enabled will disable instruction tracing


0x8AE3 - Instruction Trace Enable

 If the debugger is enabled (via --enable-debugger), sending 0x8AE3 to port 0x8A00
 after the device has been enabled will enable instruction tracing


0x8AE4 - Register Trace Disable

 If the debugger is enabled (via --enable-debugger), sending 0x8AE4 to port 0x8A00
 after the device has been enabled will disable register tracing.


0x8AE5 - Register Trace Enable

 If the debugger is enabled (via --enable-debugger), sending 0x8AE5 to port 0x8A00
 after the device has been enabled will enable register tracing. This currently
 output the value of all the registers for each instruction traced.
 Note: instruction tracing must be enabled to view the register tracing


0x8AFF

 Disable the I/O interface to the debugger and the memory monitoring functions.
</screen>
<note><para>all accesses must be done using word</para></note>
<note><para>reading this register will return 0x8A00 if currently activated, otherwise 0</para></note>
</para>
</section>
<section><title>Access to port 0x8A01 (write-only)</title>
<para>
All accesses to this port must be done using words. Writing to this port will shift
to the left by 16 the current value of the register and add the provided value to it.
<screen>
Sample:

reg0 = 0x01234567

out port: 0x8A01 data: 0xABCD

reg0 = 0x4567ABCD
</screen>
</para>
</section>
<section><title>Sample</title>
<para>
Enable memory monitoring on first page of text screen (0xb8000-0xb8fa0):
add in bochrc file: <command>optromimage1: file=&quot;asmio.rom&quot;, address=0xd0000</command>
<screen>
/*
 *      Make asmio ROM file:
 *      gcc -c asmio.S
 *      objcopy -O binary asmio.o asmio.rom
 */
        .text
        .global start
        .code16

/* ROM Header */
        .byte 0x55
        .byte 0xAA
        .byte 1                 /* 512 bytes long */

start:
/* Monitor memory access on first page of text screen */
        mov     $0x8A00,%dx     /* Enable iodebug (0x8A00->0x8A00) */
        mov     %dx,%ax
        out     %ax,%dx
        mov     $0x8A01,%ax     /* Select register 0 start addr (0x8A01->0x8A00) */
        out     %ax,%dx
        mov     $0x8A01,%dx     /* Write start addr 0xB8000 (high word first) */
        mov     $0xB,%ax
        out     %ax,%dx
        mov     $0x8000,%ax     /* Write start addr (low word) */
        out     %ax,%dx

        mov     $0x8A02,%ax     /* Select register 1 end addr (0x8A02->0x8A00) */
        mov     $0x8A00,%dx
        out     %ax,%dx
        mov     $0x8A01,%dx     /* Write end addr 0xB8FA0 (high word first) */
        mov     $0xB,%ax
        out     %ax,%dx
        mov     $0x8FA0,%ax     /* Write end addr (low word) */
        out     %ax,%dx

        mov     $0x8A00,%dx     /* Enable addr range memory monitoring (0x8A80->0x8A00) */
        mov     $0x8A80,%ax
        out     %ax,%dx

        mov     $0x8A00,%dx     /* Return to Bochs Debugger Prompt (0x8AE0->0x8A00) */
        mov     $0x8AE0,%ax
        out     %ax,%dx
        lret

        .byte 0x6b              /* Checksum (code dependent!, update it as needed) */
        .align 512              /* NOP follow */
</screen>
</para>
</section>
</section>
</chapter>

<chapter id="coding"><title>Coding</title>
<section><title>Coding guidelines</title>
<para>
<itemizedlist>
<listitem><para><command>Don't make use of any external C++ classes.</command></para>
<para>They are not offered on all platforms and this would make Bochs non-portable.
There is use of such classes in the optional debugger. I plan on removing this use.
</para></listitem>
<listitem><para><command>Don't use fancy C++ features.</command></para>
<para>Bochs is incredibly performance sensitive, and will be increasingly so as
more speed enhancements are added. There's a time and place for most everything
and this is not it. Some advanced features create overhead in the generated code
that you don't see. They also convolute the code, and sometimes occlude that is
really going on.
<itemizedlist>
<listitem><para>Don't use templates</para></listitem>
<listitem><para>Don't use virtual functions if not strictly required</para></listitem>
<listitem><para>Don't use C++ exceptions</para></listitem>
</itemizedlist></para></listitem>
<listitem><para><command>Use soft tabs.</command></para>
<para>At least when you submit code, convert all hard tabs to spaces.
There is no uniform way to handle tabs properly.</para></listitem>
<listitem><para><command>Please do compile with all warnings turned on.</command></para>
<para>It's really difficult to spot interesting warnings when a compile is littered
with non-interesting ones.</para></listitem>
<listitem><para><command>Don't use signed ints where unsigned will do.</command></para></listitem>
<listitem><para><command>Make sure that contributed code / patches are LGPL compatible.</command></para></listitem>
</itemizedlist>
</para>
</section>
      <section id="patches"><title>patches:</title>
      <para>
      &FIXME;
      how to make, where to submit, what happens then?
      </para>
      </section>
<section id="svn-release"><title>Building a Bochs release</title>
<section><title>Preparing source files and SVN</title>
<para>
Update version number and strings in configure.in.
<screen>
VERSION="2.5"
VER_STRING="2.5"
REL_STRING="Build from SVN snapshot on November 27, 2011"
</screen>
In the README file you have to update version number and date. Add some
information about new features if necessary.
<screen>
Bochs x86 Pentium+ Emulator
Updated: Sun Nov 27 16:55:00 CET 2011
Version: 2.5
</screen>
In the file <filename>bochs.manifest</filename> you have to update the version
number for the Windows build.
<screen>
  version="2.5.0.0"
</screen>
Check date, update/sumup info in CHANGES. Run autoconf to regenerate configure and check them in.
Create an SVN tag that contains all files of the revision that was used in the release.
For prereleases I create a normal SVN tag like this:
<screen>
  svn mkdir tags/REL_2_5_pre1_FINAL
  svn copy trunk/bochs tags/REL_2_5_pre1_FINAL/bochs
  svn commit
</screen>
But for a real release, I make an SVN branch tag AND a normal tag.
<screen>
  svn mkdir tags/REL_2_5_FINAL
  svn copy trunk/bochs tags/REL_2_5_FINAL/bochs
  svn mkdir branches/REL_2_5
  svn copy trunk/bochs branches/REL_2_5/bochs
  svn commit
</screen>
The tag marks where the branch split off of the main trunk.
This is very useful in maintaining the branch since you can do diffs
against it.
<screen>
   svn diff tags/REL_2_5_FINAL/bochs trunk/bochs
   svn diff tags/REL_2_5_FINAL/bochs branches/REL_2_5
   etc.
</screen>
All bugfix-only releases after the final release should be created from the REL_2_5 branch.
Now you can start building packages with the sources from the created release tag.
</para>
</section>

<section><title>Building the release on win32</title>
<para>
These instructions require cygwin and MSVC++.
</para>
<para>
In Cygwin:
<screen>
  sh .conf.win32-vcpp         # runs configure
  make win32_snap             # unzip workspace, make a win32 source ZIP
</screen>
The source ZIP is now ready for upload. To build the binary package, copy it to
a windows machine, if necessary.
</para>
<para>
Open up Visual C++ and load the workspace file Bochs.sln.  Check
the Build:Set Active Project Configuration is set the way you want it.
For releases I use "Win32 Release".
</para>
<para>
To create "bochsdbg.exe" with Bochs debugger support, manually change two
lines in config.h to turn on the debugger.
<screen>
#define BX_DEBUGGER 1
#define BX_DISASM 1
</screen>
VC++ will rebuild Bochs with debugger and overwrite bochs.exe.  To avoid
trashing the non-debug version, move it out of the way while the debugger
version is being built.  Then rename the debugger version to bochsdbg.exe.
<screen>
cd obj-release
mv bochs.exe bochs-normal.exe
(build again with BX_DEBUGGER=1 this time)
mv bochs.exe bochsdbg.exe
mv bochs-normal.exe bochs.exe
</screen>
</para>
<para>
To get the docbook installed, you need to do something like this:
<itemizedlist>
<listitem> <para> make dl_docbook </para> </listitem>
<listitem> <para> copy up to date doc files </para> </listitem>
</itemizedlist>
Then you can do
<screen>
cd doc/docbook; touch */*.html
</screen>
Do make install_win32 into /tmp or someplace:
<screen>
make install_win32 prefix=/tmp/bochs-2.5
</screen>
This copies all the files into /tmp/bochs-2.5 and then creates a
binary ZIP at /tmp/bochs-2.5.zip. Rename that bochs-2.5.win32-bin.zip.
</para>
<para>
Now make the NSIS installer package (the current script is known to work with NSIS 2.44)
<screen>
cd build/win32/nsis
</screen>
Unzip the binary ZIP file into bochs-$VERSION (must match Makefile) and
then run make.
<screen>
unzip ~/bochs-2.5.zip
make
</screen>
That gives an installer called <filename>Bochs-2.5.exe</filename>. Test and upload it.
</para>
</section>
<section><title>Building the release on Linux</title>
<para>
Do a clean SVN checkout from the release tag and specify a not yet existing
directory name with the version number as the destination. Then create the
source package from this new directory.
<screen>
  svn co http://svn.code.sf.net/p/bochs/code/tags/REL_2_5_FINAL/bochs bochs-2.5
  tar czvf bochs-2.5.tar.gz --exclude=.svn bochs-2.5
</screen>
The source TAR file bochs-2.5.tar.gz is ready for upload.
</para>
<para>
The RPM will be building using the configuration in .conf.linux with
a few parameters from <command>build/redhat/make-rpm</command>.  Make any last minute changes
to .conf.linux.  Any changes will go into the source RPM. The DLX Linux demo package
will be downloaded to the Bochs root directory if it is not already present there.
<screen>
./build/redhat/make-rpm | tee ../build.txt
</screen>
This produces two rpm files in the current directory.  Test and upload.
</para>
</section>
<section><title>Creating a file release and uploading files on SF</title>
<para>
When you are ready with creating release packages you have to upload them using
the SF file manager feature. Create a subdirectory with the version number in
the <filename>bochs</filename> directory. Point the download destination to the
new directory and start uploading packages. The top of the <filename>CHANGES</filename>
file should be used as the release notes. After setting up the file properties the
new release is ready for download.
</para>
<para>
After having all files set up in the download area, don't forget to post an announcement
containing a brief summary of changes to the bochs-announce mailing list and the "Project
News" section on SF.
</para>
</section>

</section>

</chapter>

<chapter id="webmastering"><title>Webmastering</title>

<section id="project-webspace"><title>Bochs project webspace</title>
<para>
The Bochs project webspace is stored under the SF directory <filename>/home/project-web/bochs</filename>.
It can be accessed from the SF shell using SSH or with the commands <command>sftp</command>,
<command>scp</command> and <command>rsync</command>. Some parts of the directory
structure must be updated from the local CVS repository, others from Bochs SVN
(directories <filename>bochs</filename> and <filename>sfsite</filename>).
The online documentation, disk images and screenshots must be uploaded manually.
<table>
<title>Directory structure</title>
<tgroup cols="2">
<thead>
<row>
<entry>Location</entry>
<entry>Meaning</entry>
</row>
</thead>
<tbody>
<row><entry>cgi-bin</entry><entry>CGI scripts for the website</entry></row>
<row><entry>htdocs</entry><entry>root directory of the website</entry></row>
<row><entry>htdocs/doc/docbook</entry><entry>Bochs online documentation</entry></row>
<row><entry>htdocs/docs-html</entry><entry>old Bochs documentation</entry></row>
<row><entry>htdocs/guestos</entry><entry>disk images directly stored on the Bochs website</entry></row>
<row><entry>htdocs/screenshot</entry><entry>screenshots of Bochs running several guest operating systems</entry></row>
<row><entry>htdocs/svn-snapshot</entry><entry>link to current snapshot</entry></row>
<row><entry>htdocs/techspec</entry><entry>technical specifications of several hardware components</entry></row>
<row><entry>lxr</entry><entry>Bochs source browser</entry></row>
<row><entry>sfsite-cvsroot</entry><entry>local CVS repository</entry></row>
<row><entry>sitebin</entry><entry>shell scripts (e.g. for snapshot generation)</entry></row>
<row><entry>siteman</entry><entry>website manual pages</entry></row>
<row><entry>snapshot</entry><entry>SVN snapshot storage area</entry></row>
<row><entry>tmp</entry><entry>temp directory for shell scripts</entry></row>
</tbody>
</tgroup>
</table>
</para>
</section>

<section id="update-website"><title>Updating the Bochs website content</title>
<para>
The main HTML content of the Bochs website (except online documentation) is stored
in the <filename>sfsite</filename> directory of the Bochs SVN repository. Unlike
other SF projects you don't need to upload these files to the Bochs project webspace.
Running a simple SVN update on the SF shell is enough after the files have been
updated in the repository. Please see <link linkend="svn-write-access-setup">Setting
up SVN write access</link> for general instructions. The only difference is the
directory name <filename>sfsite</filename> instead of <filename>bochs</filename>.
The example below shows how to start the SF shell with SSH and to update the
HTML files.
<screen>
ssh -t vruppert,bochs@shell.sourceforge.net create
vruppert,bochs@shell.sourceforge.net's password:

Requesting a new shell for "vruppert" and waiting for it to start.
queued... starting...

This is an interactive shell created for user vruppert,bochs.
Use the "timeleft" command to see how much time remains before shutdown.
Use the "shutdown" command to destroy the shell before the time limit.
For path information and login help, type "sf-help".

[vruppert@shell-24002 ~]$ cd /home/project-web/bochs/htdocs/
[vruppert@shell-24002 htdocs]$ svn update
U    index.html
Updated to revision 10752
[vruppert@shell-24002 htdocs]$ shutdown
Requesting that your shell be shut down.
This request will be processed soon.
[vruppert@shell-24002 htdocs]$
Broadcast message from root (Mon Oct 31 09:45:04 2011):

The system is going down for system halt NOW!
Connection to shell-24002 closed by remote host.
Connection to shell-24002 closed.
Connection to shell.sourceforge.net closed.
</screen>
</para>
</section>

<section id="update-svn-snapshot"><title>Updating the SVN snapshot</title>
<para>
The SVN snapshot
<footnote>
<para>The SVN snapshot link can be found on the bottom of the page
<filename>getcurrent.html</filename>.</para>
</footnote>
can be updated with SF shell access using SSH. There is a script
called <command>update-svn-snapshot.sh</command> that can do all the required steps
(checking out SVN, packing the source tree into one archive, updating the website
link). See previous section how to create a shell.
<screen>
cd /home/project-web/bochs/sitebin/
./update-svn-snapshot.sh
</screen>
</para>
</section>

<section id="update-online-docs"><title>Updating the online documentation</title>
<para>
To update the online documentation, a file called <filename>bochsdoc.tar.gz</filename>
must be generated with the <command>make</command>. This file must be uploaded
to the location of the online documentation on SF using <command>scp</command>.
<screen>
cd doc/docbook
make bochsdoc.tar.gz
scp bochsdoc.tar.gz vruppert,bochs@web.sf.net:htdocs/doc/docbook
</screen>
After a successful upload, the HTML files must be unpacked from the SF shell.
See section <link linkend="update-website">Updating the Bochs website content</link>
how to create a shell.
<screen>
cd /home/project-web/bochs/htdocs/doc/docbook
tar xvzf bochsdoc.tar.gz
</screen>
The updated files can be accessed from the sidebar of the Bochs website.
</para>
</section>

      <section id="other-content"><title>other content</title>
      <para>
      &FIXME; sources, tmp
      </para>
      </section>

      <section id="available-tools"><title>available tools</title>
      <para>
      &FIXME; sources, tmp
      </para>
      </section>

</chapter>
</book>