buffer_bytes not multiple of period_bytes

buffer_bytes not multiple of period_bytes

[Carlos Munoz]

Hi all,

I just noticed that alsa doesn't allocate a buffer size that is a 
multiple of the period size. For example when aplay plays a 8000 sample 
rate wav file, the driver gets the following:

    buf_bytes=8000
    period_bytes=1024

How am I going to dma the last period ?

I verified that the 16000 sample rate also has the same problem. 
However, when the sample rate is 44100 the buffer size is a perfect 
multiple of the period size.

Thanks,


Carlos Munoz


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Re: buffer_bytes not multiple of period_bytes

[Jaroslav Kysela]

On Wed, 19 Apr 2006, Carlos Munoz wrote:

> Hi all,
> 
> I just noticed that alsa doesn't allocate a buffer size that is a 
> multiple of the period size.

Yes, it's not guaranteed. The period size determines the time period to 
acknowledge transfers and these boundaries might shift across the ring 
buffer.

						Jaroslav

-----
Jaroslav Kysela <perex@suse.cz>
Linux Kernel Sound Maintainer
ALSA Project, SUSE Labs


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RE: buffer_bytes not multiple of period_bytes

[Giuliano Pochini]

On 20-Apr-2006 Carlos Munoz wrote:
> Hi all,
>
> I just noticed that alsa doesn't allocate a buffer size that is a
> multiple of the period size.

It's not required. If it is not a multiple, then the IRQ happens
in different points of the ring buffer each round. On some cards
this is hard or impossible to do. In those cases you can add this
constraint:

if ((err = snd_pcm_hw_constraint_integer(runtime, SNDRV_PCM_HW_PARAM_PERIODS)) < 0)
    return err;


--
Giuliano.


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Re: buffer_bytes not multiple of period_bytes

[Carlos Munoz]

Giuliano Pochini wrote:

>On 20-Apr-2006 Carlos Munoz wrote:
>  
>
>>Hi all,
>>
>>I just noticed that alsa doesn't allocate a buffer size that is a
>>multiple of the period size.
>>    
>>
>
>It's not required. If it is not a multiple, then the IRQ happens
>in different points of the ring buffer each round. On some cards
>this is hard or impossible to do. In those cases you can add this
>constraint:
>
>if ((err = snd_pcm_hw_constraint_integer(runtime, SNDRV_PCM_HW_PARAM_PERIODS)) < 0)
>    return err;
>
>
>  
>
Hi Giuliano,

Yes, that solved the problem.

Thanks,


Carlos


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