[Qemu-devel] Re: [PATCH] alsaaudio: increase default buffer sizes

[Jan Kiszka <jan.kiszka@web.de>]

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malc wrote:
> On Fri, 2 May 2008, Jan Kiszka wrote:
> 
>> Sound though the ALSA driver is skipping here unless I increase the
>> buffer size. OSS seems to use 16K as well, and 1K was obviously to small
>> for recording anyway.
>>
>> [ PS: Can someone explain to me why I also have to override the
>> DAC/ADC_FIXED_FREQ to 48000 to make ALSA work? Suboptimal... ]
> 
> How exactly it doesn't work if you don't override it? Do you get any
> messages prefixed with "alsa:"? As for the defaults they were set to
> 1024/256 because that's what was needed to make it sound on par with OSS
> on the two machines i had at the time.

alsa: Could not initialize ADC
alsa: Failed to set period size 256
alsa: Reason: Invalid argument
alsa: Could not initialize ADC
alsa: Failed to set period size 256
alsa: Reason: Invalid argument
audio: Failed to create voice `wm8750.input1'
alsa: Could not initialize ADC
alsa: Failed to set period size 256
alsa: Reason: Invalid argument
alsa: Could not initialize ADC
alsa: Failed to set period size 256
alsa: Reason: Invalid argument
audio: Failed to create voice `wm8750.input2'
alsa: Could not initialize ADC
alsa: Failed to set period size 256
alsa: Reason: Invalid argument
alsa: Could not initialize ADC
alsa: Failed to set period size 256
alsa: Reason: Invalid argument
audio: Failed to create voice `wm8750.input3'
alsa: Could not initialize DAC
alsa: Failed to set period size 256
alsa: Reason: Invalid argument
alsa: Could not initialize DAC
alsa: Failed to set period size 256
alsa: Reason: Invalid argument
audio: Failed to create voice `wm8750.speaker'
alsa: Could not initialize DAC
alsa: Failed to set period size 256
alsa: Reason: Invalid argument
alsa: Could not initialize DAC
alsa: Failed to set period size 256
alsa: Reason: Invalid argument
audio: Failed to create voice `wm8750.headphone'
alsa: Could not initialize DAC
alsa: Failed to set period size 256
alsa: Reason: Invalid argument
alsa: Could not initialize DAC
alsa: Failed to set period size 256
alsa: Reason: Invalid argument
audio: Failed to create voice `wm8750.monomix'

BTW, I picked up those ALSA settings from user reports on kvm-devel,
dating back to mid of last year. So I'm not alone, and it shouldn't be a
wm8750-specific thing.

> 
> By the by: OSSs fragment size is specified in bytes, ALSAs on the other
> hand in frames. So 16*1024 in the patch bellow means(considering
> S16/stereo) 65536 bytes large buffer and 1024 bytes large period. For
> OSS it's 16K bytes buffer and 4096 bytes period.
> 

Ah, OK. However, 4*1024 is not enough for the DAC here, and there were
similar reports by kvm users.

Jan


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