[linux-audio-user] latency questions

G. M. Bodnar greg at sapheron.org
Tue Oct 15 22:45:00 EDT 2002

D R Holsbeck is on permanent record as saying:
:On Tue, 2002-10-15 at 17:48, G. M. Bodnar wrote:
:> First off, I'll mention that I'm using a Dell Inspiron 2650 laptop.
:> I'm running debian unstable with 2.4.19.
:I a,m running the same setup on an IBM A31 Thinkpad, and do not have
:problems with latencies. Even while running 24chs in Ardour, using a an
:RME H-DSP interface. So I would venture that your problem has more to do
:with Dell than Linux.

I'm pretty certain of this actually.  This is the first problem I've had
with linux+alsa in quite some time.

:> 1) DMA transer won't enable.  I've enabled DMA transfers in the kernel
:> as suggested by the howto.  However, I'm unable to turn on dma access
:> with hdparm.  I'm told the operation is not permitted.
:More evidence that it is a hardware issue. Or hardeware/software
:incompatibiliy to be more politicly correct.

After a lot more poking around, it seems as if this is fixed in a
prerelease for 2.4.20.  I'll have to sneaker-net some patches home with
me tonight.

:> 2) IRQ mess.  dmesg lists that almost every device that is detected is
:> on irq 10, including the onboard sound (i8x0) and video card (nVidia).
:> As a result, in X, I get static and pops as the audio is delayed.
:> Searching further, I noticed a message saying the APIC wasn't being used
:> due to a buggy bios provided by Dell.  This could explain why everything
:> is pushed to IRQ 10.
:All my devices end up on 11, but APIC takes care of things nicely.

I'll have to do some more testing around this, then.  Maybe buffering
would clean things up a bit.

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