201 lines
8.1 KiB
Plaintext
201 lines
8.1 KiB
Plaintext
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Installing Line Disciplines and Streams Modules
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Description
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Most radio and modem clocks used for a primary (stratum-1) NTP server
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utilize serial ports operating at speeds of 9600 baud or greater. The
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timing jitter contributed by the serial port hardware and software
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discipline can accumulate to several milliseconds on a typical Unix
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workstation. In order to reduce these errors, a set of special line
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disciplines can be configured in the operating system process. These
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disciplines intercept special characters or signals provided by the
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radio or modem clock and save a local timestamp for later processing.
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The disciplines can be compiled in the kernel in older BSD-derived
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systems, or installed as System V streams modules and either compiled in
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the kernel or dynamically loaded when required. In either case, they
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require reconfiguration of the Unix kernel and provisions in the NTP
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daemon xntpd. The streams modules can be pushed and popped from the
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streams stack using conventional System V streams program primitives.
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Note that not all Unix kernels support line disciplines and of those
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that do, not all support System V streams. The disciplines here are
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known to work correctly with SunOS 4.x kernels, but have not been tested
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for other kernels.
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There are two line disciplines included in the distribution. Support for
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each is enabled by adding flags to the DEFS_LOCAL line of the build
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configuration file ./Config.local. This can be done automatically by the
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autoconfiguration build procedures, or can be inserted/deleted after the
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process has completed.
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tty_clk (CLK)
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This discipline intercepts characters received from the serial port
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and passes unchanged all except a set of designated characters to
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the generic serial port discipline. For each of the exception
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characters, the character is inserted in the receiver buffer
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followed by a timestamp in Unix timeval format. Both select() and
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SIGIO are supported by the discipline. The -DCLK flag is used to
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compile support for this disipline in the NTP daemon. This flag is
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included if the clkdefs.h file is found in the /sys/sys directory,
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or it can be added (or deleted) manually.
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tty_chu (CHU)
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This discipline is a special purpose line discipline for receiving
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a special timecode broadcast by Canadian time and frequency
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standard station CHU. The radio signal is first demodulated by the
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300-baud modem included in the gadget box, then processed by the
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discipline and finally processed by the Scratchbuilt CHU Receiver
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discipline (type 7). This discipline should be used in raw mode.
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The -DCHU flag is used to compile support for this disipline in the
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NTP daemon. This flag is included if the chudefs.h file is found in
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the /sys/sys directory, or it can be added (or deleted) manually.
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There are two sets of line disciplines. The tty_clk.c and chu_clk.c are
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designed for use with older BSD systems and are compiled in the kernel.
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The tty_clk_STREAMS.c and chu_clk_STREAMS.c are designed for use with
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System V streams, in which case they can be either compiled in the
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kernel or dynamically loaded. Since these disciplines are small,
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unobtrusive, and to nothing unless specifically enabled by an
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application program, it probably doesn't matter which method is choosen.
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Compiling with the Kernel
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The following procedures are for the tty_clk line discipline; for the
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chu_clk, change "tty" to "chu".
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1. Copy tty_clk.c into /sys/os and clkdefs.h into /sys/sys.
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2. For SunOS 4.x systems, edit /sys/os/tty_conf.c using some facsimile
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of the following lines:
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#include "clk.h"
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...
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#if NCLK > 0
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int clkopen(), clkclose(), clkwrite(), clkinput(), clkioctl();
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#endif
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...
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#if NCLK > 0
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{ clkopen, clkclose, ttread, clkwrite, clkioctl,
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clkinput, nodev, nulldev, ttstart, nullmodem, /* 10 CLK */
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ttselect },
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#else
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{ nodev, nodev, nodev, nodev, nodev,
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nodev, nodev, nodev, nodev, nodev,
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nodev },
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#endif
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For Ultrix 4.x systems, edit /sys/data/tty_conf_data.c using some
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facsimile of the following lines:
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#include "clk.h"
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...
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#if NCLK > 0
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int clkopen(), clkclose(), clkwrite(), clkinput(), clkioctl();
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#endif
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...
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#if NCLK > 0
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clkopen, clkclose, ttread, clkwrite, clkioctl, /* 10 CLK */
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clkinput, nodev, nulldev, ttstart, nulldev,
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#else
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nodev, nodev, nodev, nodev, nodev,
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nodev, nodev, nodev, nodev, nodev,
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#endif
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If the kernel doesn't include the ??select() entry in the structure
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(i.e., there are only ten entry points in the structure) just leave
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it out. Also note that the number you give the line discipline (10
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in most kernels) will be specific to that kernel and will depend on
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what is in there already. The entries sould be in order with no
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missing space; that is, if there are only seven disciplines already
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defined and you want to use 10 for good reason, you should define a
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dummy 9th entry like this:
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nodev, nodev, nodev, nodev, nodev, /* 9 CLK */
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nodev, nodev, nodev, nodev, nodev,
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3. Edit /sys/h/ioctl.h and include a line somewhere near where other
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line disciplines are defined like:
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#define CLKLDISC 10 /* clock line discipline */
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The "10" should match what you used as the number in the preceding
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step.
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4. Edit /sys/conf/files and add a line which looks like:
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sys/tty_clk.c optional clk
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5. Edit the kernel configuration file to include the following:
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pseudo-device tty 4 # TTY clock support
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6. Run config, then make clean, then make depend, then make vmunix,
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then reboot the new kernel.
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Installing as a streams module
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The following procedures are for the tty_clk_STREAMS line discipline;
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for the tty_chu_STREAMS, change "clk" to "chu".
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1. Copy your choice to /sys/os, removing the "_STREAMS" in the
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filename.
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2. Copy the clkdefs.h file to /usr/include/sys, then construct a soft
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link to /sys/sys.
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3. Append to /sys/conf.common/files.cmn:
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os/tty_tty.c optional tty
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4. Edit /sys/sun/str_conf.c. You'll want to add lines in three places.
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It'll be sort of clear where when you see the file.
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#include "tty.h"
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...
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#if NTTY > 0
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extern struct streamtab ttyinfo;
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#endif
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...
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#if NTTY > 0
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{ "tty", &ttyinfo },
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#endif
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5. Edit /sys/[arch]/conf/[k-name] (substituting the architecture and
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kernel name) to stick in:
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pseudo-device tty 4 # TTY clock support
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You can change "4" to anything you like. It will limit the number
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of instantiations of the tty discipline you can use at the same
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time.
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6. Run config, then make clean, then make depend, then make vmunix,
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then reboot the new kernel.
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Both disciplines can be dynamically loaded using streams procedures
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specific to the kernel. Before using the chu_clk discipline, all other
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streams modules that may already be on the stack should be popped, then
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the discipline should be pushed on the stack.
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How to Use the tty_clk Line Discipline
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The tty_clk line discipline defines a new ioctl(), CLK_SETSTR, which
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takes a pointer to a string of no more than CLK_MAXSTRSIZE characters.
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Until the first CLK_SETSTR is performed, the discipline will simply pass
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through characters. Once it is passed a string by CLK_SETSTR, any
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character in that string will be immediately followed by a timestamp in
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Unix timeval format. You can change the string whenever you want by
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doing another CLK_SETSTR. The character must be an exact, 8 bit match.
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The character '\000' cannot, unfortunately, be used, as it is the string
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terminator. Passing an empty string to CLK_SETSTR turns off stamping.
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Passing NULL will produce undefined results.
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How to Use the tty_chu Line Discipline
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The tty_chu line discipline translates data received from the CHU modem
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and returns chucode structures, as defined in chudefs.h, and expected by
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the Scratchbuilt CHU Receiver reference clock driver. Depending on the
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settings of PEDANTIC and ANAL_RETENTIVE used when compiling the kernel,
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some checking of the data may or may not be necessary.
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David L. Mills (mills@udel.edu)
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