/*
* This driver furnishes an interface for pulse-per-second (PPS) signals
* produced by a cesium clock, timing receiver or related equipment. It
* can be used to remove accumulated jitter over a congested link and
* retime a server before redistributing the time to clients. It can
*also be used as a holdover should all other synchronization sources
* beconme unreachable.
*
* Before this driver becomes active, the local clock must be set to
* within +-0.4 s by another means, such as a radio clock or NTP
* itself. There are two ways to connect the PPS signal, normally at TTL
* levels, to the computer. One is to shift to EIA levels and connect to
* pin 8 (DCD) of a serial port. This requires a level converter and
* may require a one-shot flipflop to lengthen the pulse. The other is
* to connect the PPS signal directly to pin 10 (ACK) of a PC paralell
* port. These methods are architecture dependent.
*
* This driver requires the Pulse-per-Second API for Unix-like Operating
* Systems, Version 1.0, RFC-2783 (PPSAPI). Implementations are
* available for FreeBSD, Linux, SunOS, Solaris and Tru64. However, at
* present only the Tru64 implementation provides the full generality of
* the API with multiple PPS drivers and multiple handles per driver. If
* the PPSAPI is normally implemented in the /usr/include/sys/timepps.h
* header file and kernel support specific to each operating system.
*
* This driver normally uses the PLL/FLL clock discipline implemented in
* the ntpd code. Ordinarily, this is the most accurate means, as the
* median filter in the driver interface is much larger than in the
* kernel. However, if the systemic clock frequency error is large (tens
* to hundreds of PPM), it's better to used the kernel support, if
* available.
*
* This deriver is subject to the mitigation rules described in the
* "mitigation rulse and the prefer peer" page. However, there is an
* important difference. If this driver becomes the PPS driver according
* to these rules, it is acrive only if (a) a prefer peer other than
* this driver is among the survivors or (b) there are no survivors and
* the minsane option of the tos command is zero. This is intended to
* support space missions where updates from other spacecraft are
* infrequent, but a reliable PPS signal, such as from an Ultra Stable
* Oscillator (USO) is available.
*
* Fudge Factors
*
* The PPS timestamp is captured on the rising (assert) edge if flag2 is
* dim (default) and on the falling (clear) edge if lit. If flag3 is dim
* (default), the kernel PPS support is disabled; if lit it is enabled.
* If flag4 is lit, each timesampt is copied to the clockstats file for
* later analysis. This can be useful when constructing Allan deviation
* plots. The time1 parameter can be used to compensate for
* miscellaneous device driver and OS delays.
*/
/*
* Interface definitions
*/
#define DEVICE "/dev/pps%d" /* device name and unit */
#define PRECISION (-20) /* precision assumed (about 1 us) */
#define REFID "PPS\0" /* reference ID */
#define DESCRIPTION "PPS Clock Discipline" /* WRU */
/*
* PPS unit control structure
*/
struct ppsunit {
struct refclock_atom atom; /* atom structure pointer */
int fddev; /* file descriptor */
};
/*
* Open PPS device. This can be any serial or parallel port and
* not necessarily the port used for the associated radio.
*/
snprintf(device, sizeof(device), DEVICE, unit);
up->fddev = tty_open(device, O_RDWR, 0777);
if (up->fddev <= 0) {
msyslog(LOG_ERR,
"refclock_atom: %s: %m", device);
return (0);
}
/*
* Light up the PPSAPI interface.
*/
return (refclock_ppsapi(up->fddev, &up->atom));
}
/*
* atom_shutdown - shut down the clock
*/
static void
atom_shutdown(
int unit, /* unit number (not used) */
struct peer *peer /* peer structure pointer */
)
{
struct refclockproc *pp;
struct ppsunit *up;
pp = peer->procptr;
up = pp->unitptr;
if (up->fddev > 0)
close(up->fddev);
free(up);
}
/*
* atom_timer - called once per second
*/
void
atom_timer(
int unit, /* unit pointer (not used) */
struct peer *peer /* peer structure pointer */
)
{
struct ppsunit *up;
struct refclockproc *pp;
char tbuf[80];
pp = peer->procptr;
up = pp->unitptr;
if (refclock_pps(peer, &up->atom, pp->sloppyclockflag) <= 0)
return;
peer->flags |= FLAG_PPS;
/*
* If flag4 is lit, record each second offset to clockstats.
* That's so we can make awesome Allan deviation plots.
*/
if (pp->sloppyclockflag & CLK_FLAG4) {
snprintf(tbuf, sizeof(tbuf), "%.9f",
pp->filter[pp->coderecv]);
record_clock_stats(&peer->srcadr, tbuf);
}
}
/*
* atom_poll - called by the transmit procedure
*/
static void
atom_poll(
int unit, /* unit number (not used) */
struct peer *peer /* peer structure pointer */
)
{
struct refclockproc *pp;
/*
* Don't wiggle the clock until some other driver has numbered
* the seconds.
*/
if (sys_leap == LEAP_NOTINSYNC)
return;
