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

[Dave Hart]

On Thu, May 10, 2012 at 6:31 AM, Eric S. Raymond <esr at thyrsus.com> wrote:
> Dave Hart <davehart_gmail_exchange_tee at davehart.net>:
>> 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)

I understand gpsd's flexibility when providing PPS timestamping using
TIOCMIWAIT.  My impression, without auditing a bunch of code, is that
PPSAPI implementations in OSes commonly are watching only the CD line.
 That's the case with the few I've looked at closely, although they're
not among the most commonly used.

Cheers,
Dave Hart