Hi All,
I am writing an application on an ARM based embedded computer. And have
found a few difficulties with the process. Any help or explanations on the
following points would be appreciated.
1. The hardware is running at an incorrect clock rate. This causes a +-46.8
kHz frame rate to be supplied to the CPU. When I compile the kernel with
this value as the ALSA clock I get "double the error" (i.e. an actual data
rate of [requested data rate]*(46.8/48)*(46.8/48) bps). But when I compile
it with an ALSA clock rate of 49.1 kHz (i.e. fix it with 48000*(desired
clock rate)/(actual clock rate)) an actual stream of 48kHz is reproduced
(i.e. [requested data rate] * (46.8/48 {hardware fault})*(48/46.8) {49.1kHz
setting in kernel}) My question is, why does it work "the wrong way round"?
Should one not supply the actual hardware clock rate, instead of a
"corrected" clock rate?
2. I have noticed that recording with the "snd_pcm_readi" function uses 30%
of the CPU (I have tried blocking and non-blocking modes). As well as
registering a callback, again blocking and non-blocking, as well as using
poll/select (blocking and non-blocking). The best I can do is 30% CPU load,
which seems a lot. 'arecord' also uses 30% CPU (measured with 'top'). The
strange thing is that 'aplay' hardly uses any CPU power (2-3%). Any ideas
how I can reduce the CPU loading? Is this an ARM limitation? A known ALSA
driver/library problem? An implementation problem? Any other ideas?
I am not sure what information would be required, but my configuration is as
follows:
ARM based PC-104 CPU running at 400MHz - The Viper PC-104 SBC from Arcom
UK, running a Debian based Linux kernel tailored for the CPU, Linux 2.6.13
(patched) to run on the Viper, to correct the ALSA clock rate and some FLASH
issues.
I am not sure how to obtain the version of ALSA itself, amixer, aplay and
arecord all return a version of 1.0.8.
I am a bit reluctant to try and compile a new version of the ALSA drivers
and libraries since I do not know what changes would be required to get it
to work on this embedded CPU.
Regards,
Rudi
Rudi van der Linde
[EMAIL PROTECTED]
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