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SubjectRe: LinuxPPS low-level IRQs timestamps & ldisc
On Mon, Jun 02, 2008 at 07:51:13AM +0100, Alan Cox wrote:
> > First I added a new dcd_change() ldisc method which can be used as
> > follow:
>
> This looks good.

:)

> >
> > static void pps_tty_dcd_change(struct tty_struct *tty, unsigned int status)
> > {
> > int id = (int) tty->disc_data;
> > struct timespec __ts;
> > struct pps_ktime ts;
> >
> > /* First of all we get the time stamp... */
> > getnstimeofday(&__ts);
> >
> > /* ... and translate it to PPS time data struct */
> > ts.sec = __ts.tv_sec;
> > ts.nsec = __ts.tv_nsec;
> >
> > /* Now do the PPS event report */
> > pps_event(id, &ts,
> > status ? PPS_CAPTUREASSERT : PPS_CAPTURECLEAR, tty);
> >
> > pr_debug("[STDev] PPS %s at %lu on source #%d\n",
> > status ? "assert" : "clear", jiffies, id);
> > }
> >
> > However this solution gives very low precision timestamps so that's
>
> Where are you calling it from, and how ?

From serial_core.h as follow:

static inline void
uart_handle_dcd_change(struct uart_port *port, unsigned int status)
{
struct uart_info *info = port->info;
struct tty_ldisc *ld = tty_ldisc_ref(info->tty);

if (ld->dcd_change)
ld->dcd_change(info->tty, port->irq, status);
tty_ldisc_deref(ld);

port->icount.dcd++;

if (info->flags & UIF_CHECK_CD) {
if (status)
wake_up_interruptible(&info->open_wait);
else if (info->tty)
tty_hangup(info->tty);
}
}

> > 2) The new dcd_change() method is well implemented? Can I add the
> > "irq" parameter or I can find it somewhere?
>
> Not all tty devices have an IRQ (I suspect those which do not are useless
> for PPS reporting however).

Yes. Those devices are completely useless.

> Do you get decent reports if you change the tty driver to do
>
> getnstimeofday(&ts);
> [blah blah lots of serial port I/O code]
> if (dcd ^ old_dcd)
> ld->dcd_change(tty, dcd, &ts);
>
> ??

It could be a bit better... I did as above since I supposed that you
wished all PPS code should be removed from serial port code.

However, using your suggestion, I can do:

static inline void
uart_handle_dcd_change(struct uart_port *port, unsigned int status)
{
struct uart_info *info = port->info;
struct tty_ldisc *ld = tty_ldisc_ref(info->tty);
struct pps_ktime ts;

#ifndef CONFIG_PPS_IRQ_EVENTS
struct timespec __ts;

/* First of all we get the time stamp... */
getnstimeofday(&__ts);

/* ... and translate it to PPS time data struct */
ts.sec = __ts.tv_sec;
ts.nsec = __ts.tv_nsec;
#else
/* Get the IRQ timestamp from system array */
ts = pps_irq_ts[irq];
#endif

if (ld->dcd_change)
ld->dcd_change(info->tty, status, &ts);
tty_ldisc_deref(ld);

...

This is better then ever! :)

Thanks,

Rodolfo

--

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


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