[alsa-devel] [PATCH v5 1/2] amidi: add delay option

[Clemens Ladisch]

Felipe Ferreri Tonello wrote:
> On 23/08/16 11:37, Clemens Ladisch wrote:
>> Felipe Ferreri Tonello wrote:
>>> On 22/08/16 13:43, Clemens Ladisch wrote:
>>>> Felipe F. Tonello wrote:
>>>>> +				if (data > send_data)
>>>>> +					usleep(delay * 1000);
>>>>
>>>> The MIDI data is sent asynchonously, so this delay is not _between_ messages.
>>>> You'd have to add 320 µs for any byte not yet sent (I guess you have to use
>>>> snd_rawmidi_status_get_avail() to find out how many have been sent).
>>>
>>> Right. Or I can just use snd_rawmidi_drain()?
>>
>> This function not only drains the ALSA buffer, but also waits for the
>> hardware FIFO to empty.  And most drivers do not implement this, in
>> which case the framework just does a fixed wait of 50 ms, which would
>> correspond to a FIFO size of 156 bytes.
>
> Ok, so does that mean that it is not safe to use drain()?

That additional 50 ms delay might be safe, but not what you want.


Regards,
Clemens