[Thumbgps-devel] Article -- Macx-1: GPS receiver with standard USB connector and PPS support

[tz]

But this requires a recompile to change lines, not a command line option,
or some detection method.  If gpsd is compiled for RI, it wont respond to
DCD.
On May 10, 2012 2:31 AM, "Eric S. Raymond" <esr at thyrsus.com> wrote:

> Dave Hart <davehart_gmail_exchange_tee at davehart.net>:
> > While I appreciate GPSD's flexibility, I advise against exercising it
> > needlessly.  All of the PPSAPI implementations which support serial
> > port control line input that I'm aware of want to see it on the
> > carrier detect line.  If you know you'll only ever care about using
> > the hardware with GPSD, any control line will do for PPS, but to use
> > it directly with ntpd, the PPSAPI implementations dictate using the
> > DCD line.
> >
> > I had a vague recollection GPSD could use PPSAPI where it's available.
> >  If that's true, when GPSD is using PPSAPI, isn't it restricted to
> > using carrier detect in practice?
>
> Which line the PPS arrives on is a hardware feature of the GPS completely
> decoupled from anything PPSAPI has any control over.
>
> There's no code-complexity cost for being flexible.  Here's what the
> code looks like:
>
> #define PPS_LINE_TIOC (TIOCM_CD|TIOCM_CAR|TIOCM_RI|TIOCM_CTS)
>
>    /*
>     * Wait for status change on any handshake line. The only assumption
> here
>     * is that no GPS lights up more than one of these pins.  By waiting on
>     * all of them we remove a configuration switch.
>     */
>    while (1) {
>        int ok = 0;
>        char *log = NULL;
>        char *log1 = NULL;
>
>        if (ioctl(session->gpsdata.gps_fd, TIOCMIWAIT, PPS_LINE_TIOC) != 0)
> {
>            gpsd_report(LOG_ERROR, "PPS ioctl(TIOCMIWAIT) failed: %d
> %.40s\n"
>                , errno, strerror(errno));
>            break;
>        }
>
> That definition of PPS_LINE_TIOC is quite literally the only place in
> GPSD where the identity of the PPS pin matters. It used to not include
> TIOCM_CTS, but we got a bug report from someone using sonething called
> an "Xtreme104 12 port serial board" which actually mungs all the
> handshake lines into CTS.
> --
>                <a href="http://www.catb.org/~esr/">Eric S. Raymond</a>
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