Re: Weird sound problems on Dell Latitude C840 resolved..

[Andrew McGregor <andrew@indranet.co.nz>]

These are general Dell laptop problems, and so far as I can tell, there's 
no solution yet to either.  Audio is quite hard (except to get apps to use 
bigger buffers; try googling for 'hammerfall cardbus dell', it's a common 
problem).

This page:
http://www-106.ibm.com/developerworks/library/l-hw2.html
may contain a solution to the audio issue, too, I just discovered.

The clock problem is something Linux should deal with.  Like to look into 
it?  I can help somewhat.

Andrew


--On Tuesday, January 14, 2003 01:14:31 -0500 Valdis.Kletnieks@vt.edu wrote:

> A while back, I reported nasty sound distortion/echoing problems
> on a C840.  Well, this is a follow-up that I found the cause of the
> problem...
>
> I was also running gkrellm, with it's APM monitor activated.  Whenever
> it read from /proc/apm, this would cause a call to the BIOS down in
> apm_get_power_status().  As near as I can tell, on this particular Dell,
> calling the APM drops interrupts on the floor even if you run with
> CONFIG_APM_ALLOW_INTS.  Another effect of this was a badly drifting
> clock (which is how I found this in the first place) - doing a
> a 'grep timer /proc/interrupts', waiting 4 or 5 minutes of wall clock
> time, doing it again, and doing the math showed only 980 or so interrupts
> per second.  The clock drift exhibits itself under 2.4.18 as well,
> but it wasn't breaking audio.
>
> My guess is that the 2.4 driver for the i810 audio is a bit more tolerant
> of the occasional dropped interrupt (it seems to like to keep a lot of
> data already queued in the ring buffer), but the 2.5 driver runs in much
> more 'just in time' mode.  As a result, if the kernel gets suspended while
> we monkey around in the BIOS, we get a data underrun, causing my problems.
>
> For what it's worth, the i8k plugin for gkrellm also causes clock drift,
> but doesn't seem to upset the audio driver.
>
> (OK, so it's not as glorious as debugging APIC issues on a NUMAQ system.
> On the other hand, there's probably a lot more Latitudes out there than
> NUMAQ boxes, and more importantly to *me*, I have to deal with this
> particular Latitude 8-10 hours a day.  And somebody made a comment about
> open source being driven to scratch itches... ;)
>
> /Valdis
>