[linux-audio-user] snd-hdsp+cardbus=distortion -- the
sagacontinues (cardbus driver=culprit?) UPDATE: 99.9% sure it is the
cardbus driver yenta_socket
TimBlechmann at gmx.net
Tue Mar 30 15:10:38 BST 2004
> What needs to happen is that the card driver author needs to
> investigate what is going on, and, if it seems related to the core
> PCMCIA core or the socket driver, we need to get involved.
he pointed out that it's probably a kernel problem ...
we don't want you to solve problems of the alsa driver, but we suspect
there is a problem with the cardbus bridge...
1.) the card is a combination of 2 devices: a interface device, either a
pci or a cardbus card, and a dsp device, either digital or analog
audio ... no problems have ever been reported about the pci
interface, so it's likely to be a problem with the cardbus interface
... although i have to admit, that there are only 3 reported systems
that have the problems, we experience ... but these systems are
completely different ones (p4 / amd64, different cardbus bridges)
2.) the dsp device has an internal matrix mixer, that's independant from
the computer (this audio data isn't sent to the computer at all) ...
in fact it's possible to set the matrix mixer and unplug the dsp
device from the computer ...
there are three problems, that show the situation:
3.) if we start an audio application that produces interrupts on the
hdsp device, some of the audio data that's been transfered to the
computer will be copied or mapped to the buffer of the audio data
that's been transfered from the computer to the corresponding
output. this could either happen
- inside the device itself (i doubt that, since the same driver, the
same firmware, the same devices are working without and problems
on other linux machines or with windows on the same machine)
- inside the cardbus bridge
- inside the kernel
4.) if we start the audio playback, the audio playback seems to be
one block of samples will be followed by one block of samples of 0
(zero) ... note that these block are not the blocks of data, that
are sent to the hdsp during one interrupt. it's usually 32 samples
of sound followed by 32 samples of silence, the driver sends blocks
of 64 to 8192 during one interrupt depending on user settings...
iirc one sample is 24 bit
on the other hand the blocks of silence aren't missing, but the alsa
layer will adapt, so that it takes twice as long as it should to
play back a soundfile (i'm not sure if it's because of the alsa
soundfile player or of the driver)
5.) the reason why we (or at least i) think, that it's a problem with
the cardbus interface, is because of jack's output ...
jack is both an audio connection interface for different softwares
and a very good alsa implementation... using jack as super user
in realtime mode, it complains about latency problems:
delay of xxx usecs exceeds estimated spare time of yyy; restart ...
at the default sample rate of 48000 xxx only about 0.06 % bigger
than yyy ... on the other hand, i only get this error on sample
rates of more than 32000 ... although the sound at 32000 is
distorted, as well...
other thoughts i had:
6.) the distortion isn't affected by the block size / the number of
it is affected by the samplerate ... that's why i think, there are
always 32 samples (768 bit) followed by 32 samples of silence (768
bit zero ???)
7.) the problems occured on different cardbus bridges:
ENE C1410 (ico / mandrake)
o2micro6933 (myself / gentoo)
Texas Instruments PCI1250 (timothy / red hat)
i don't know what's the reason for the problems, the latency or the
mapping problem, or if there is something else that results this problem
... but since it's a software and not a hardware issue (works fine with
windows), i'd like to get into it, and at least try to solve it ... but
since i'm neiter a kernel hacker nor i have any idea about the hardware
internals, i'd need some help from some people, who are able to help
me... i don't want some people to solve my problems for me, but i'd
appreciate any help of people, who know what's going on inside the
Tim mailto:TimBlechmann at gmx.de
The only people for me are the mad ones, the ones who are mad to live,
mad to talk, mad to be saved, desirous of everything at the same time,
the ones who never yawn or say a commonplace thing, but burn, burn,
burn, like fabulous yellow roman candles exploding like spiders across
the stars and in the middle you see the blue centerlight pop and
everybody goes "Awww!"
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