[linux-audio-dev] USB-MIDI Transfer rate

[Clemens Ladisch]

Jens M Andreasen wrote:
> On Fri, 2005-09-16 at 09:52 +0200, Clemens Ladisch wrote:
> > > The MIDI-USB device also have a control channel without any endpoints
> > > (without any physical midi-jacks.) Again only as far as I have
> > > understood; the control channel is not a MidiStream and should therefore
> > > be able to accept a significantly higher transfer rate than the physical
> > > MidiStreams.
> >
> > Control transfers always involve an answer sent by the other device,
> > and multiple control transfers cannot be sent in parallel, so the data
> > rate would be rather low.
>
> In the specific case, I get that the transfer rate on the control equals
> a normal midi stream. The data sent to the control is normal midi data.

Are you speaking about the device's control pipe or about a MIDI port
that happens to be labeled "control"?  The former _cannot_ be used to
send MIDI data, and the latter is just a standard USB MIDI stream.

> Are you absolutely sure that it is not possible to increase the thruput?

Try changing the line:

	ep->max_transfer = usb_maxpacket(umidi->chip->dev, pipe, 1);

in the snd_usbmidi_out_endpoint_create function in usbmidi.c to:

	ep->max_transfer = 512;

or even bigger values.  This should result in more than one packet per
frame.


It would be interesting to know what the maximum data rate is.


Regards,
Clemens