Full-duplex questions

Guenter Geiger guenter.geiger at psp-vie.be.philips.com
Mon Dec 21 19:29:44 CET 1998

Hi !

Yes, you are right, full duplex doesn´t work correctly.
I just never had a card, which is full duplex until now (bought a PCI128 too).

I realized the same problems as you did:
1) with OSS/Free, the card only works in full duplex with BIG
   audiobuffer sizes.(kernel 2.1.131)
2) Didn´t try OSS/Linux, because it crashed my computer (alpha)
   the last time I installed it. You could try setting the audiobuffer
   size and look if it works ..
3) After trying ALSA I realized, that the ALSA code in pd is only
   full duplex with two soundcards. Then, I´m having problems with ALSA under
   Alpha anyway, which I have to investigate further.

In my opinion the OSS driver just don´t work as documented, or rather, the
lacks a specification of minimum audiobuffer sizes.

What I will do against it:

- Look if I can tweak the code, so that it will work under OSS/Free.
- Try to make the ALSA support clean.
- Investigate the possibility of 4 channel output :)

until then (early Jan), you could only look into s_linux.c and try to fix
OSS code yourself..

Merry Christmas


> -----Original Message-----
> From: Michael Lechasseur [mailto:mlecha at music.mcgill.ca]
> Sent: Saturday, December 19, 1998 10:07 AM
> To: PD List
> Subject: Full-duplex questions
> I'm having problems with full-duplex mode in Linux.
> I'm using a Sound Blaster PCI128 with OSS/Linux and
> alternately with ALSA
> drivers.
> The ALSA drivers seem very nice BTW, a bit of pain to setup,
> but they sound
> great.
> With OSS/Linux I get this message when starting pd:
> pd: dacs died.. switching to alternate time source
> the same error occours with the -adc switch, -dac works fine.
> Using the ALSA drivers, which are full duplex, pd starts in
> -dac mode even
> if it the switch is not specified. ie: I get the "write only"
> message from
> pd.
> Using the ALSA compatible mixer "xamixer" I can mix multiple
> inputs with no
> problems while listening to the output.
> I don't know if this is the best way to test full-duplex
> capabilities in
> Linux?  Any ideas?
> Does pd support 16-bit full-duplex audio?  It seems to work
> ok in win95.
> Thanks.

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