Question

我目前正在尝试将来自GPS接收器（如UBlox ZED-F9P）的PPS信号连接到运行Ubuntu Mate 18.04和GPSD的Raspberry Pi。我已经验证了PPS内核模块是否存在，并且RPi确实通过以下命令检测到PPS信号：

$ ppstest /dev/pps0
trying PPS source "/dev/pps0"
found PPS source "/dev/pps0"
ok, found 1 source(s), now start fetching data...
source 0 - assert 1559136628.231481270, sequence: 631 - clear  0.000000000, sequence: 0                   │
...

现在的问题是，当我运行GPSD时，出现以下错误：

$ gpsd -nND8 /dev/ttyACM0 /dev/pps0
...
gpsd:PROG: KPPS:/dev/pps0 Assert cycle:  999997, duration:       0 @  1559136675.231397794
gpsd:RAW: PPS:/dev/pps0 Assert pps-detect invisible pulse
gpsd:PROG: PPS:/dev/pps0 Assert cycle:  999997, duration:       0 @  1559136675.231397794
gpsd:PROG: PPS:/dev/pps0 Assert rejected missing last_fixtime
gpsd:PROG: KPPS:/dev/pps0 assert  1559136676.231395175, sequence: 679, clear   0.000000000, sequence: 0 -
 using: assert
...

再深入一点源代码，可以发现GPSD在将PPS脉冲与某个时间相关联时遇到了问题。如（gpsd/ppsthread.c中所述，同时在脉冲时刻计算系统时间与GPS时间之间的偏移量（差）。

/*
 * If there has not yet been any valid in-band time stashed
 * from the GPS when the PPS event was asserted, we can do
 * nothing further.  gpsd can not tell what second this pulse is
 * in reference to.
 *
 * Some GPSes like Garmin always send a PPS, valid or not.
 * Other GPSes like some uBlox may only send PPS when time is valid.
 * It is common to get PPS, and no fixtime, while autobauding.
 */
/* FIXME, some GPS, like Skytraq, may output a the fixtime so
 * late in the cycle as to be ambiguous. */
if (last_fixtime.real.tv_sec == 0) {
    /* probably should log computed offset just for grins here */
    ok = false;
    log = "missing last_fixtime\n";
} else if ( ok && last_second_used >= last_fixtime.real.tv_sec ) {
    /* uh, oh, this second already handled */
    ok = false;
    log = "this second already handled\n";
}

if ( !ok ) {
    /* can not use this pulse, reject and retry */
    thread_context->log_hook(thread_context, THREAD_PROG,
        "PPS:%s %.10s ignored %.100s",
        thread_context->devicename, edge_str,  log);
    continue;
}

我的问题是如何解决此问题，以便可以将GPSD与Chrony一起使用来设置NTP服务器。

GPSD在将PPS与时间关联时遇到问题（Ublox ZED-F9P）

0 个答案: