cycle time for synchronisation (my whishlist entry)

[Manfred W. <e95...@st...>]

Hi!

Since the 1394 cycle time register provides a very accurate clock, it
would be a perfect means for synchronisation purposes. I would like to
use it for synchronisation of the video and audio frames of a DVB
stream. But there is one big problem. If I liked to present a frame at a
given cycle time T, I would have to use a code like this:

 quadlet_t buf;
 do
   raw1394_read(rawhandle, 0xffc0 | raw1394_get_local_id(handle),
                CSR_CYCLE_TIME, 4, &buf);
 while (T > buf);
 presentFrame();

The problem is, that this is busy waiting and therefore very cpu
consuming.

So it would be nice, if we could find a way to register something to get
an information, when a given cycle time is reached. My idea is to
register a callback funktion for that purpose. Consider this example:

 int timestamp_reached;
 int timer_callback()
 {
    timestamp_reached=1;
    return 0;
 }

 ...

 raw1394_set_cycletime_handler(rawhandle, T, timer_callback);
 timestamp_reached=0;
 while (!timestamp_reached)
    raw1394_loop_iterate(rawhandle);
 presentFrame();

I believe that this would be cleaner, because raw1394_loop_iterate is -
afaik - blocking, and therefore this would not be busy waiting.

So my question is, if it is possible to implement something like
"raw1394_set_cycletime_handler" in the example above or something
similar (another way would be not to register a callbackfunction, but
just the address of a variable which will be incremented, when libraw
receives the message, that the time was reached).
And if it is possible, can you imagine to implement it in the near
future? I think, that would be a really nice feature.

Manfred Weihs