[ntp:questions] Re: PPS API

Rodolfo Giometti giometti at linux.it
Sat Apr 16 16:58:58 UTC 2005


Sorry for delay...

On Fri, Apr 08, 2005 at 02:39:55PM +0200, Ulrich Windl wrote:
> What I undertstood is that this is simply still all in kernel space; right?
> What should be the benefits from your point of view?

The benefits are:

* by using the netlink layer we can divide the PPSAPI from a
particular driver (you don't need to modify the serial driver so
heavy).

* the PPSAPI can be the same for all PPS source (currently in
PPSkit-light-PPSAPI-alpha-1610m-2.6.5 there are duplicated functions
whose do the same things: do_clock_gettime(), pps_update_event(),
etc.)

* by using the exported kernel symbols we can manage the PPS source
with few and simple functions calls. For example, once you register a
PPS source into the kernel with:

   static struct linuxpps_source_info_s linuxpps_ktimer_info = {
      name		: "my PPS source",
      mode		: PPS_CAPTUREASSERT|PPS_OFFSETASSERT|PPS_ECHOASSERT| \
		          PPS_CANWAIT|PPS_TSFMT_TSPEC,
      echo 	        : linuxpps_ktimer_echo,
   };

   ...

   source = linuxpps_register_source(&linuxpps_ktimer_info, ...);

you can signal an assert event (for example in the interrupt handler
routine) just using:

   linuxpps_event(source, PPS_CAPTUREASSERT);

The same function may also runs the defined echo function
(linuxpps_ktimer_echo()) if the user asked for that... etc.

I'm just working on it and I hope to be able to post some alpha
version of my code as soon as possible, so you can see it and give me
back some suggestions.

Thanks,

Rodolfo

-- 

GNU/Linux Solutions                  e-mail:    giometti at linux.it
Linux Device Driver                             giometti at enneenne.com
Embedded Systems                     home page: giometti.enneenne.com
UNIX programming                     phone:     +39 349 2432127
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