---------- Forwarded message ----------
From: klondike <franxisco1988@xxxxxxxxx>
Date: 2008/7/1
Subject: Re: which are the pieces of ALSA source code
responsible for setting sample rate ?
To: stan <ghjeold_i_mwee@xxxxxxx>
on asoundrc you can fix the rate when you set the slave:
slave.pcm "hw:0,0"
# slave {
# pcm "hw:0,0" # you cannot use a "plug" device here, darn.
# period_time 0
# period_size 1024 # must be power of 2
# buffer_size 8192 # dito. It
# format "S32_LE"
# periods 128 # dito.
# rate 192000 # with rate 8000 you *will* hear,
# if ossmix is used :)
# }
2008/7/1 stan <ghjeold_i_mwee@xxxxxxx>:
> Sergei Steshenko wrote:
>> -----Original Message-----
>> From: stan <ghjeold_i_mwee@xxxxxxx>
>> To: Sergei Steshenko <steshenko_sergei@xxxxxxx>
>> Date: Tue, 01 Jul 2008 06:50:50 -0700
>> Subject: Re: which are the ieces of ALSA source code responsiblefor setting sample rate ?
>>
>>
>>> Sergei Steshenko wrote:
>>>
>>>> Hello All,
>>>>
>>>> as already known, I am one of those who advocate the possibility to mandate sample rate and not let applications to change it.
>>>>
>>>> I think a possible, though ugly, solution is like this:
>>>>
>>>> 1) to locate pieces of ALSA code responsible for setting sample rate;
>>>> 2) to change (in my own copy) the pieces so they would know only one sample rate;
>>>> 3) to compile and install the modified code.
>>>>
>>>> I also think that I would like to have an ALSA snapshot per sample rate and will uninstall/install the snapshot I need
>>>> - most likely the two most used will be for 44100Hz and 48000Hz sample rates.
>>>>
>>>> So, which are the pieces ?
>>>>
>>>> Thanks,
>>>> Sergei.
>>>>
>>>>
>>>>
>>> Why not write a small program that calls the alsa interface and sets the
>>> rate to whatever you want. This must be how the applications you are
>>> concerned about are doing it. The api call is snd_pcm_hw_params_set_rate.
>>>
>>> From the alsa-project api
>>>
>>> int snd_pcm_hw_params_set_rate ( snd_pcm_t
>>> <http://www.alsa-project.org/alsa-doc/alsa-lib/group___p_c_m.html#gb5676348e7618b444e28907607660cef>
>>> * /pcm/,
>>>
>>>
>>> snd_pcm_hw_params_t
>>> <http://www.alsa-project.org/alsa-doc/alsa-lib/group___p_c_m.html#g232a2e2b6bb7bb2dca2885eec2e095b3>
>>> * /params/,
>>>
>>>
>>> unsigned int /val/,
>>>
>>>
>>> int /dir/
>>>
>>> )
>>>
>>>
>>>
>>> Restrict a configuration space to contain only one rate.
>>>
>>> *Parameters:*
>>>
>>> /pcm/ PCM handle
>>>
>>> /params/ Configuration space
>>>
>>> /val/ approximate rate
>>>
>>> /dir/ Sub unit direction
>>>
>>> *Returns:*
>>> 0 otherwise a negative error code if configuration space would
>>> become empty
>>>
>>> Wanted exact value is <,=,> val following dir (-1,0,1)
>>>
>>>
>>>
>>
>> As was many times explained in this list, applications can change the rate.
>>
>> So, if I write and run such a program, and then start an application that can change sample rate, it will, and this is what I want
>> to avoid.
>>
>> I was thinking of modifying the piece of code which reports audio card capabilities - if such a piece exists.
>>
>> For each version (for each sample rate) the piece of code will report just _one_ sample rate, so hopefully the rest of ALSA won't
>> even try to set a different sample rate.
>>
>> Thanks,
>> Sergei.
>>
>>
> I remember seeing the rates hard coded somewhere in the alsa tree. I
> can't remember if it was in the lib code or the driver code. You could
> have alternate versions of the routine with those rates. Load the
> alternate when you want to lock the rate. Just follow the set...rate
> call above to see where it is looking, and change the return from that
> to only return the rate you want.
>
> There might be another way that is simpler to do this that someone more
> knowledgeable than me can describe. I'm thinking of the configuration
> data or in an asoundrc.
>
>
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