Re: Underruns (borken pipes)

[Bruce Paterson <bruce@tele-ip.com>]

Paul Davis wrote:
> 
> >I got around my previous problems (readn) in an output/capture
> >application with an envy24
> >(ice1712) by bypassing the plugin and going straight to hw:0,0. Had to
> >change my code a bit
> >but it's now **almost** working.
> 
> i humbly suggest that you:
> 
>   (1) read the source code for JACK's ALSA driver/client
>   (2) consider using JACK

I did, but the Jack introduction frankly scared me off a bit. I'm sure
that it's not its
intention, but the talk about necessary mods to the kernel and
synchronisation issues between
channels (I&O) seemed a huge amount of bother to go to at the time.
Maybe (based on your comments)
it's necessary evil afterall anyway.

> the first suggestion will reveal quite a bit. you additionally will
> need to know that you can't avoid underruns with small buffer sizes
> unless you run with SCHED_FIFO or SCHED_RR scheduling, and not without

You know nothing in the alsa docs even hints at this, well certainly not
in all the
PCM bits I went through. Actually it IS working 90% of the time at
present, as long
as; 
a) I leave lots of RAM (don't run X etc)
b) I bash away at write/read regardless every 10ms in my hacky version
of code (the "poll" version
is a disaster)
Could you possibly give me some pointers as to where to look in the Jack
code ? I am totally
unfamilier with it.

> a kernel with Andrew Morton's low latency patches. you didn't say what
> buffer sizes you were using, so its hard to know if this is an issue.

I did actually:
>>Output frame buffer size is 6553, and input 5461, as returned by the
>>hardware.
Nothing bigger can be assigned.

I have my own frame buffer for tx of full channel width 10, and another
for rx of channel
width 12. Each is only the frame sizes above only.
I have on top of that my own buffers (non interleaved) for my 4 capture
channels and 1
output channel. These are typically 40s at 96000 long * 32bits....all
are preallocated.
I copy from these in/out of the tx/rx frame buffers prior/after a
sucessful write/read
call.

Also, if my plughw:0,0 interface to the envy24 doesn't work (segfault in
the plug code),
whereas the hw:0,0 does, will Jack even work ??
-- 
Cheers,
Bruce
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