Hammerfall DSP: Midi-related audio dropouts workaround / question

["M. Nentwig" <nentwig@users.sourceforge.net>]

Hello,

a couple of days I wrote about audio dropouts caused by MIDI data.
Now I found a workaround: Unloading the uhci (USB) driver, loading the
hammerfall driver, reloading the uhci driver gets rid of the dropouts.
Also plugging in a USB device helps. Both USB controller and hdsp share
the same interrupt on my laptop.

Before I found this workaround, I spent some time hacking the hdsp
driver. I created a new thread, that sleeps
('interruptible_sleep_on(sth)'), until the MIDI interrupt wakes it
('wake_up'(sth)). As long as it's doing no real work (just counting MIDI
events for example), everything works fine.
But as soon as I take the MIDI processing out of the interrupt (or
remove it completely), the machine locks up. Probably during the
interrupt - even the 'magic sysrq key' is dead. And I don't understand
this at all. Does the hardware crash, if I don't empty the MIDI FIFO
queue in time?
The crash occurs also, when MIDI processing is removed from a vanilla
hdsp driver.

Some related observations:
- The dropouts disappear, if I disable MIDI interrupts. But then MIDI in
is unreliable, big surprise.
- The dropouts don't get any better, if I don't submit the received data
to alsa at the end of the MIDI-in processing.

Regards

Markus



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