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trident noise

Hey there --

I've recently been tinkering with VIA's EPIA motherboard and the
various gizmos integrated into VIA's "super southbridge" chip.
Basically everything is crammed into this chip:

00:00.0 Host bridge: VIA Technologies, Inc. VT8601 [Apollo ProMedia] (rev 05)
00:01.0 PCI bridge: VIA Technologies, Inc. VT8601 [Apollo ProMedia AGP]
00:11.0 ISA bridge: VIA Technologies, Inc. VT8231 [PCI-to-ISA Bridge] (rev 10)
00:11.1 IDE interface: VIA Technologies, Inc. Bus Master IDE (rev 06)
00:11.2 USB Controller: VIA Technologies, Inc. UHCI USB (rev 1e)
00:11.3 USB Controller: VIA Technologies, Inc. UHCI USB (rev 1e)
00:11.4 Bridge: VIA Technologies, Inc. VT8235 Power Management (rev 10)
00:11.5 Multimedia audio controller: VIA Technologies, Inc. AC97 Audio Controller (rev 40)
00:12.0 Ethernet controller: VIA Technologies, Inc. Ethernet Controller (rev 51)
00:13:0 Kitchen sink: VIA Technologies, Inc. Sink (rev 08) Faucet (rev 11b)
01:00.0 VGA compatible controller: Trident Microsystems CyberBlade/i1 (rev 6a)

(all right, 00:13 is fictional)

The problem I've been having is something I've not seen much since AGP
came around - the sound card chirps and skips when you move a window
around.  I've tried everything I can think of to reproduce the problem
in other ways, but I'm pretty confidant that I've isolated it to X.
Playing with DMA mode on the disk, unloading the network driver,
blasting the CPU to induce latency and all permutations of such abuse
fail to cause the sound card to skip. In fact, it sounds pretty good
for inexpensive hardware. However, as soon as X is loaded and a window
is perturbed, the sound card goes insane.

Now, if I remember my history, PCI video card manufacturers discovered
at some point that they could lengthen the little bars produced by
WinBench by a few percent if they wrote blindly to the instruction
queue on the video card. This didn't cause trouble for most PCI
devices, but it caused that obnoxious popping and squeaking from sound
cards. The PCI bus would lock up for a few tens of audio cycles -
insignificant for filesystem performance, but you will definitely hear
(and hate) it. The only way to fix it was to put the code that checks
the video instruction queue back into the video driver.

I'm not sure if my problem is caused by the same issue. I _think_ the
AGP bus is a thing apart from the PCI bus, so careless video drivers
should no longer play havoc on sound cards. Of course, this is a
completely integrated system, so I pretty much have to take VIA's word
that they are logically isolated (they certainly aren't physically
isolated - they're masked onto the same silicon). So, it could be a
hardware bug.

I can't imagine that Branden had anything to do with this, so is
probably an upstream problem. I figure it couldn't hurt to ask,
though. Any ideas?



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