Re: [PATCH v2 1/1] alsa-lib: Add snd_pcm_start_at.

[Tim Cussins <timcussins@eml.cc>]

On 06/01/15 14:42, Pierre-Louis Bossart wrote:
>
>>> Do your implementation need to set specific start threshold to prevent
>>> the driver automatically start when you fill the buffer ?
>>
>>
>>> Do the driver allow to start when there is no data ?
>>>
>>
>> It's the responsibility of the client to set the start threshold to a
>> safe and responsible value.
>>
>> It might suit some applications to allow both threshold start _and_
>> start_at: My implementation doesn't preclude this.
>
> Now I am confused... My understanding was that this feature is similar
> to SSYNC in HDAudio, where everything is ready, buffers filled, DMAs
> armed, FIFOs filled and the start condition only opens the last gate at
> a specific time - possibly with multiple streams starting at the same
> time. If you add a condition on the start_threshold you really don't
> need any hardware-driven start, do you?

What you've described is exactly what I had in mind, so we're still on 
the same page.

I wanted to make it clear that my implementation of start_at doesn't 
*prevent* client code starting on a threshold *and* using start_at, even 
if it seems to us like a strange idea.

Preventing the use of both requires us to show why it's never a useful 
idea, decide on policy (what do happens when client code tries to use 
both), and implement that policy. I'd rather just leave it as 'possible' :)

> Thanks,
> -Pierre
>
>
>