Underruns (borken pipes)

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

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'm now running into underrun problems...occasionally.
I am outputting and capturing at 32 bits, 96000 on 4 input channels and
1 output (but of course
using hw:0,0 its actually 10 output & 12 input hard-wired). All IO is
being stored in RAM buffers
and I'm not running into swap.

Is my machine simply not fast enough ? (700MHz Pentium, 500M RAM) Help
!!!

What I don't understand is this:

If I put write & read in a loop, with a small 10ms delay, setup both in
& out to be non-blocking, I
get only occasional underruns. Underruns are unacceptable in my
application so I have to completely
abort. About every 2nd call to read or write gets an EAGAIN, as you
would expect.

If, however, I use file descriptor polling before read and write; don't
attempt a write till
POLLOUT, or a read until POLLIN or POLLPRI, but have the whole lot in a
big loop so I handle
either as soon as they require, I get failures EVERY time I run.
Somewhere about the 5th
hardware buffer iteration. Underrun is randomly on read or write. Doing
the code "properly"
seems to be far worse !
I never get EAGAIN from read/write in this case, and I haven't seen a
poll failure yet.

Output frame buffer size is 6553, and input 5461, as returned by the
hardware.

As far as I can see I'm roughly complying with the example code
/test/pcm.c with transfer method
"write and wait for room in buffer using poll"
-- 
Cheers,
Bruce
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