Re: Trigger Callback

[Julien Bramary <julien.bramary@blueyonder.co.uk>]

Takashi Iwai wrote:
> At Tue, 01 Aug 2006 21:14:24 +0100,
> Julien Bramary wrote:
>   
>> Lee Revell wrote:
>>
>>     
>>>>  > "PCM engine" refers to the hardware's PCM engine, not ALSA's.  It's 100%
>>>>  > device dependent - you need to consult the docs for your sound device to
>>>>  > determine how to start the PCM.
>>>>  >
>>>>  > Lee
>>>>         
>> Thanks, I see now why it starts, I'm doing some inits in my dac in the
>> open callback... I should do those here in the trigger.
>>     
>
> Remember that the trigger callback is designed really as a "trigger".
> That is, it should be executed as shortly as possible.  The callback
> is even in the atomic context within spinlock and irq disablement, so
> any function that my sleep shall cause lockup.
>
> If you need to allocate something, it should be done in either
> open, hw_params or prepare callback.  Only start and stop are done in
> trigger callback.
>
>
> Takashi
>
>   
Thanks for the reminder. I think this should be ok. The only function I 
now have in the trigger is the following 'write' (atomic enough):
   /* enable SSC data Tx */
   at91_ssc_write(AT91_SSC_CR, AT91_SSC_TXEN);

Cheers,
Julien


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