[linux-dvb] Re: AW: Re: How to send A/V-Packets without blocking the whole device

[Johannes Stezenbach <js@convergence.de>]

Roland Praml wrote:
> > Your description of what you do is rather vague. Assuming you
> > write audio to /dev/dvb/adapterX/audioY and video to
> > /dev/dvb/adapterX/videoY, why don't you use nonblocking I/O?
> 
> Yes thats right, I open the devices with O_NONBLOCK and I poll
> each device to see if i can write new data. But it seems that the 
> AUDIO device blocks also if there is enough video-data sent.
> (and the other way round)

Well, if you open the devices with O_NONBLOCK write() should never
block...

> btw. it doesn't matter if I fed the audio-LPCM frames in the
> audio or video device, because the data stream is demultiplexed
> in somewher the AV7110 again, and if the demx buffer is full
> both devices are blocked. 

I assume by "block" you mean that poll() isn't woken up?
The ability to write multiplexed audio/video PES into the video
device complicates the logic for poll() (see av7110_av.c, 
dvb_audio_poll() and dvb_video_poll() and FREE_COND).

But ultimately it is an API issue that you cannot specify whether
you want to write multiplexd a/v to one device or both seperately,
so the wake-up conditions in *_poll() cannot be fixed. Or so I think.

BTW: The firmware requests audio and video data when it has enough free
buffer space (see case DATA_MPEG_PLAY in gpioirq() in av7110.c, bits 8
and 9 in av7110->debitype request audio/video). If you fail to provide
data, then the CPU will spent a lot of time handling useless gpioirqs...

HTH,
Johannes