[alsa-devel] Steinberg MIDEX8 driver attempt

[Hedde Bosman]

Hi Clemens,

thanks for responding.

On Sun, May 28, 2017 at 10:16 PM, Clemens Ladisch <clemens at ladisch.de> wrote:
> Hedde Bosman wrote:
>> I've owned a MIDEX8 for some years now and am now attempting a driver
>> for it. [...]
>> it looks a bit like the standard usb midi class, but it requires some
>> periodic (i guess timer) messages on endpoint 0x02
>
> Why "requires"?  What happens if you do not send them?

Without sending those, the midi in does not seem to work.

>
>> Not all (interrupt) urbs that are submitted will complete (within 25
>> ms at least).
>
> And why would that be a problem?

I am not sure about the inner workings of the device. However, it
seems to be a timing signal, that might be used to time-stamp midi in
packets. I haven't been able to determine the exact impact, but did
notice that sometimes the midi-in stops responding. If that is
related, I cannot tell.

>
>> Sometimes after sending a few messages, an empty urb shows up in
>> wireshark. However, in code, there's an if-statement that should allow
>> only messages of length > 0 to be submitted (line 568, if (num_read >
>> 0)).
>
> Try adding a check before the actual usb_submit_urb() call, but nothing
> would protect against your code accidentally changing the
> transfer_buffer_length of an active URB field later.

I will try and report back later.

>
>> Might this have to do with issue 1?
>
> Not unless you have mixed up input and output URBs.

afaik I did not. I am looking for better ways to debug though.

>
>
> Regards,
> Clemens

Regards, Hedde