Re: [Jack-Devel] Call for testing of MIDI Drivers in JACK 2

On Wed, Apr 6, 2011 at 10:57 PM, Clemens Ladisch <[hidden]> wrote:
> Devin Anderson wrote:
>> When I first did research for writing this driver, I was looking
>> through the ALSA kernel code, and noticed that the default behavior
>> for the 'drain' method (when a driver doesn't set its own rawmidi
>> 'drain' method) is to sleep for 50 milliseconds, and then return,
>> regardless of whether blocking I/O is used or not.  So, one of the
>> things I did with the 'alsarawmidi' driver is to call:
>>
>>     snd_rawmidi_params_set_avail_min(rawmidi, params, 1);
>
> This already is the default value.

Okay.

>> ... to make the driver wake up when any bytes are written to a port,
>> and to avoid calling `snd_rawmidi_drain` completely.
>
> The avail_min parameter controls only wakeups of the application.

I made a bad assumption.  In my defense, the ALSA API documentation is
a bit lacking in details. :)

> The drain method is used only with output devices to wait for all data
> in ALSA's buffer to be written to the device.  The only situation where
> you would want to call it is when closing the device, where ALSA already
> calls it automatically.

Right.  The JACK ALSA raw driver calls 'snd_rawmidi_drain' after each
successful call to 'snd_rawmidi_write'.  Since one thread is handling
output to all ports, couldn't that cause some ports to be neglected?

-- 
Devin Anderson
devin (at) charityfinders (dot) com

CharityFinders - http://www.charityfinders.com/
synthclone - http://synthclone.googlecode.com/

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