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

[malc]

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.

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.

> Signed-off-by: Jan Kiszka <address@hidden>
> ---
> audio/alsaaudio.c |    6 +++---
> 1 file changed, 3 insertions(+), 3 deletions(-)
>
> Index: b/audio/alsaaudio.c
> ===================================================================
> --- a/audio/alsaaudio.c
> +++ b/audio/alsaaudio.c
> @@ -58,7 +58,7 @@ static struct {
>     int period_size_out_overridden;
>     int verbose;
> } conf = {
> -#define DEFAULT_BUFFER_SIZE 1024
> +#define DEFAULT_BUFFER_SIZE 16*1024
> #define DEFAULT_PERIOD_SIZE 256
> #ifdef HIGH_LATENCY
>     .size_in_usec_in = 1,
> @@ -72,8 +72,8 @@ static struct {
>     .buffer_size_out = 400000,
>     .period_size_out = 400000 / 4,
> #else
> -    .buffer_size_in = DEFAULT_BUFFER_SIZE * 4,
> -    .period_size_in = DEFAULT_PERIOD_SIZE * 4,
> +    .buffer_size_in = DEFAULT_BUFFER_SIZE,
> +    .period_size_in = DEFAULT_PERIOD_SIZE,
>     .buffer_size_out = DEFAULT_BUFFER_SIZE,
>     .period_size_out = DEFAULT_PERIOD_SIZE,
>     .buffer_size_in_overridden = 0,

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