[linux-dvb] Re: Are frontend events queued?

[Johannes Stezenbach <js@convergence.de>]

On Wed, Jul 21, 2004 at 07:31:36PM +0200, Wolfgang Fritz wrote:
> Hello,
> 
> I'm trying to get some facts about the infamous "video data stream
> broken" error in VDR.
> 
> The following modified code from VDR-1.3.10/dvbdevice.c cDvbTuner::Action
> 
>   active = true;
>   while (active) {
>         ....
>         if (tunerStatus == tsTuned) {
>            fe_status_t status = fe_status_t(0);
>            CHECK(ioctl(fd_frontend, FE_READ_STATUS, &status));
>            if (status & FE_HAS_LOCK) {
>               tunerStatus = tsLocked;
> 	      dsyslog ("Frontend %d locked", cardIndex);
> 	      }
>            }
>         if (tunerStatus != tsIdle) {
>            dvb_frontend_event event;
>            if (ioctl(fd_frontend, FE_GET_EVENT, &event) == 0) {
> 	      dsyslog ("Event on frontend %d: %02x", cardIndex, event.status);
>               if (event.status & FE_REINIT) {
>                  tunerStatus = tsSet;
>                  esyslog("ERROR: frontend %d was reinitialized -
> re-tuning", cardIndex);
>                  continue;
>                  }
>               }
>            }
>      ....
>         bool fast = (tunerStatus == tsTuned) || (ciHandler &&
> (time(NULL) - startTime < 20));
>         newSet.TimedWait(mutex, fast ? 100 : 1000);
>         }
> 
> sometimes gives the following output:
> 
> Jul 21 19:06:21 vdr vdr[1697]: Event on frontend 1: 00
> Jul 21 19:06:21 vdr vdr[1697]: Frontend 1 locked
> Jul 21 19:06:21 vdr vdr[1697]: Event on frontend 1: 03
> Jul 21 19:06:22 vdr vdr[1697]: Event on frontend 1: 1f
> 
> What does this mean?
> 
> - Did the frontend really lose lock for a short time?
> 
> Or
> 
> - Are the frontend events queued so that the event "03"
> in fact occured before the "Frontend 1 locked"?

Events are queued. You are supposed to use poll() and read
events as soon as they are generated, or let FE_GET_EVENT
block waiting for events. To fix up vdr you could also
open the frontend with O_NONBLOCK and loop until
FE_GET_EVENT returns -EGAIN, discarding old events.

Once upon a time szap did something like that:
http://linuxtv.org/cgi-bin/cvsweb.cgi/DVB/apps/szap/szap.c?rev=1.3.2.1&content-type=text/plain


Johannes