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doc: Expanded introductory text.

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Martin Ling 2015-05-24 13:47:38 +01:00 committed by Uwe Hermann
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libserialport.h.in
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@ -29,27 +29,56 @@
* By writing your serial code to use libserialport, you enable it to work
* transparently on any platform supported by the library.
*
* The operations that are supported are:
*
* - @ref Enumeration (obtaining a list of serial ports on the system)
* - @ref Ports
* - @ref Configuration (baud rate, parity, etc.)
* - @ref Signals (modem control lines, breaks, etc.)
* - @ref Data
* - @ref Waiting
* - @ref Errors
*
* libserialport is an open source project released under the LGPL3+ license.
*
* API principles
* ==============
* The library is maintained by the [sigrok](http://sigrok.org/) project. See
* the [libserialport homepage](http://sigrok.org/wiki/Libserialport) for the
* latest information.
*
* The API is simple, and designed to be a minimal wrapper around the serial
* port support in each OS.
* Source code is maintained in git at
* [git://sigrok.org/libserialport](http://sigrok.org/gitweb/?p=libserialport.git).
*
* Most functions take a pointer to a struct sp_port, which represents a serial
* port. These structures are always allocated and freed by the library, using
* the functions in the @ref Enumeration "Enumeration" section.
* Bugs are tracked at http://sigrok.org/bugzilla/.
*
* The library was conceived and designed by Martin Ling, is maintained by
* Uwe Hermann, and has received contributions from several other developers.
* See the git history for full credits.
*
* API information
* ===============
*
* The API has been designed from scratch. It does not exactly resemble the
* serial API of any particular operating system. Instead it aims to provide
* a set of functions that can reliably be implemented across all operating
* systems. These form a sufficient basis for higher level behaviour to
* be implemented in a platform independent manner.
*
* If you are porting code written for a particular OS, you may find you need
* to restructure things somewhat, or do without some specialised features.
* For particular notes on porting existing code, see @ref Porting.
*
* The following subsections will help explain the principles of the API.
* To jump directly into the detailed function documentation, see the
* <a href="modules.html">categorised function lists</a>.
*
* Data structures
* ---------------
*
* The library defines three data structures:
*
* - @ref sp_port, which represents a serial port.
* See @ref Enumeration.
* - @ref sp_port_config, which represents a port configuration.
* See @ref Configuration.
* - @ref sp_event_set, which represents a set of events.
* See @ref Waiting.
*
* All these structures are allocated and freed by library functions. It is
* the caller's responsibility to ensure that the correct calls are made to
* free allocated structures after use.
*
* Return codes and error handling
* -------------------------------
*
* Most functions have return type @ref sp_return and can return only four
* possible error values:
@ -75,6 +104,124 @@
* Calls that succeed return @ref SP_OK, which is equal to zero. Some functions
* declared @ref sp_return can also return a positive value for a successful
* numeric result, e.g. sp_blocking_read() or sp_blocking_write().
*
* An error message is only available via sp_last_error_message() in the case
* where SP_ERR_FAIL was returned by the previous function call. The error
* message returned is that provided by the OS, using the current language
* settings. It is an error to call sp_last_error_code() or
* sp_last_error_message() except after a previous function call returned
* SP_ERR_FAIL. The library does not define its own error codes or messages
* to accompany other return codes.
*
* Thread safety
* -------------
*
* Certain combinations of calls can be made concurrently, as follows.
*
* - Calls using different ports may always be made concurrently, i.e.
* it is safe for separate threads to handle their own ports.
*
* - Calls using the same port may be made concurrently when one call
* is a read operation and one call is a write operation, i.e. it is safe
* to use separate "reader" and "writer" threads for the same port. See
* below for which operations meet these definitions.
*
* Read operations:
*
* - sp_blocking_read()
* - sp_blocking_read_next()
* - sp_nonblocking_read()
* - sp_input_waiting()
* - sp_flush() with @ref SP_BUF_INPUT only.
* - sp_wait() with @ref SP_EVENT_RX_READY only.
*
* Write operations:
*
* - sp_blocking_write()
* - sp_nonblocking_write()
* - sp_output_waiting()
* - sp_drain()
* - sp_flush() with @ref SP_BUF_OUTPUT only.
* - sp_wait() with @ref SP_EVENT_TX_READY only.
*
* If two calls, on the same port, do not fit into one of these categories
* each, then they may not be made concurrently.
*
* Debugging
* ---------
*
* The library can output extensive tracing and debugging information. The
* simplest way to use this is to set the environment variable
* LIBSERIALPORT_DEBUG to any value; messages will then be output to the
* standard error stream.
*
* This behaviour is implemented by a default debug message handling
* callback. An alternative callback can be set using sp_set_debug_handler(),
* in order to e.g. redirect the output elsewhere or filter it.
*
* No guarantees are made about the content of the debug output; it is chosen
* to suit the needs of the developers and may change between releases.
*
* @anchor Porting
* Porting
* -------
*
* The following guidelines may help when porting existing OS-specific code
* to use libserialport.
*
* ### Porting from Unix-like systems ###
*
* There are two main differences to note when porting code written for Unix.
*
* The first is that Unix traditionally provides a wide range of functionality
* for dealing with serial devices at the OS level; this is exposed through the
* termios API and dates to the days when serial terminals were common. If your
* code relies on many of these facilities you will need to adapt it, because
* libserialport provides only a raw 8-bit channel with no special handling.
*
* The second relates to blocking versus non-blocking I/O behaviour. In
* Unix-like systems this is normally specified by setting the O_NONBLOCK
* flag on the file descriptor, affecting the semantics of subsequent read()
* and write() calls.
*
* In libserialport, blocking and nonblocking operations are both available at
* any time. If your existing code ѕets O_NONBLOCK, you should use
* sp_nonblocking_read() and sp_nonblocking_write() to get the same behaviour
* as your existing read() and write() calls. If it does not, you should use
* sp_blocking_read() and sp_blocking_write() instead. You may also find
* sp_blocking_read_next() useful, which reproduces the semantics of a blocking
* read() with VTIME = 0 and VMIN = 1 set in termios.
*
* Finally, you should take care if your program uses custom signal handlers.
* The blocking calls provided by libserialport will restart system calls that
* return with EINTR, so you will need to make your own arrangements if you
* need to interrupt blocking operations when your signal handlers are called.
* This is not an issue if you only use the default handlers.
*
* ### Porting from Windows ###
*
* The main consideration when porting from Windows is that there is no
* direct equivalent for overlapped I/O operations.
*
* If your program does not use overlapped I/O, you can simply use
* sp_blocking_read() and sp_blocking_write() as direct equivalents for
* ReadFile() and WriteFile(). You may also find sp_blocking_read_next()
* useful, which reproduces the special semantics of ReadFile() with
* ReadIntervalTimeout and ReadTotalTimeoutMultiplier set to MAXDWORD
* and 0 < ReadTotalTimeoutConstant < MAXDWORD.
*
* If your program makes use of overlapped I/O to continue work while a serial
* operation is in progress, then you can achieve the same results using
* sp_nonblocking_read() and sp_nonblocking_write().
*
* Generally, overlapped I/O is combined with either waiting for completion
* once there is no more background work to do (using WaitForSingleObject() or
* WaitForMultipleObjects()), or periodically checking for completion with
* GetOverlappedResult(). If the aim is to start a new operation for further
* data once the previous one has completed, you can instead simply call the
* nonblocking functions again with the next data. If you need to wait for
* completion, use sp_wait() to determine when the port is ready to send or
* receive further data.
*/
#ifndef LIBSERIALPORT_LIBSERIALPORT_H