[LinuxPPS] refclock_nmea patch

[Rodolfo Giometti]

On Tue, Oct 23, 2007 at 05:54:43AM +0200, Udo van den Heuvel wrote:
> 
> You mean NMEA when you say 'GPS data source'?
> I think both, looking at the code. (where the PPS API interface is started)

But when you talk about /dev/gps0 you point __only__ the GPS data
source, while you talk about /dev/pps0 you point __only__ the PPS data
source. NMEA is represented by both /dev/gps0 __and__ /dev/pps0.

> > The former is correct beacuse /dev/gps0 is _not_ a PPS source, it's a
> > serial line (points to /dev/ttyS0), the latter I don't know. :)
> 
> We open a fd on a device, do time_pps_create and when it fails, we open
> the fd on another device, do another time_pps_create...
> So the fd is not saved.
> So how can ntpd use the first device for NMEA and the second for PPS?

I don't know NMEA code but it seems to me you are working inside a
function, is the fd passed to it? If not you have to save fd
somewhere, maybe in up->fd?

> Maybe this can help:
> When is the /dev entry (pps0) created?
> Based on what input?

If you have udev when the pps device is created, otherwise you have to
create it by yourself by using mknod.

> --- org.ntp-4.2.4p2/ntpd/refclock_nmea.c	2006-06-06 22:16:53.000000000 +0200
> +++ ntp-4.2.4p2/ntpd/refclock_nmea.c	2007-10-23 05:52:09.000000000 +0200
> @@ -61,6 +61,7 @@
>  # define DEVICE "COM%d:" 	/* COM 1 - 3 supported */
>  #else
>  # define DEVICE	"/dev/gps%d"	/* name of radio device */
> +# define DEVICEPPS "/dev/pps%d" /* name of alternate PPS radio device */
>  #endif
>  #define	SPEED232	B4800	/* uart speed (4800 bps) */
>  #define	PRECISION	(-9)	/* precision assumed (about 2 ms) */
> @@ -71,6 +72,7 @@
>  #define RANGEGATE	500000	/* range gate (ns) */
>  
>  #define LENNMEA		75	/* min timecode length */
> +#define LENPPS		PPS_MAX_NAME_LEN
>  
>  /*
>   * Tables to compute the ddd of year form icky dd/mm timecode. Viva la
> @@ -231,15 +233,27 @@
>  	 * the assert edge and do not enable the kernel hardpps.
>  	 */
>  	if (time_pps_create(fd, &up->handle) < 0) {
> -		up->handle = 0;
> -		msyslog(LOG_ERR,
> -		    "refclock_nmea: time_pps_create failed: %m");
> -		return (1);
> +		/* Try the alternate PPS device */
> +                (void) sprintf(device, DEVICEPPS, unit);
> +		msyslog(LOG_ERR, "refclock_nmea: try alternate PPS device \"%s\"", device);
> +                fd = open(device, O_RDWR);

I don't know NMEA code but maybe here you are overriding the GPS data
source file descriptor... if so you should use different variable
(pps_fd?).

Can you please post the whole function you are modifying so I can
understand if the fd should be renamed or not?

> +                if (fd < 0)
> +                	goto pps_error;
> +		if (time_pps_create(fd, &up->handle) < 0)
> +               		goto pps_error;
>  	}
> +	else (void) sprintf(device, DEVICE, unit); /* just rebuild device's name */
> +	msyslog(LOG_INFO, "refclock_nmea: found PPS source \"%s\"", device);
>  	return(nmea_ppsapi(peer, 0, 0));
>  #else
>  	return (1);
>  #endif /* HAVE_PPSAPI */
> +
> +pps_error:
> +	/* No luck, no PPS unit available! */
> +	up->handle = -1;
> +	msyslog(LOG_ERR, "refclock_nmea: no PPS devices found at " DEVICE " nor " DEVICEPPS ": %m", unit, unit);
> +	return (1);
>  }
>  
>  /*
> @@ -257,8 +271,7 @@
>  	pp = peer->procptr;
>  	up = (struct nmeaunit *)pp->unitptr;
>  #ifdef HAVE_PPSAPI
> -	if (up->handle != 0)
> -		time_pps_destroy(up->handle);
> +	time_pps_destroy(up->handle);
>  #endif /* HAVE_PPSAPI */
>  	io_closeclock(&pp->io);
>  	free(up);
> @@ -366,7 +379,7 @@
>  	/*
>  	 * Convert the timespec nanoseconds field to ntp l_fp units.
>  	 */ 
> -	if (up->handle == 0)
> +	if (up->handle == -1)
>  		return (0);
>  	timeout.tv_sec = 0;
>  	timeout.tv_nsec = 0;

Ciao,

Rodolfo

-- 

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Linux Device Driver                             giometti at gnudd.com
Embedded Systems                     		giometti at linux.it
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