New subject: Weird USB MIDI sysex problem

31 Aug 2013

Gordon JC Pearce wrote:
...
  On Sat, Aug 31, 2013 at 11:34:33AM +0200, Clemens
Ladisch wrote:
  Gordon JC Pearce wrote:
  The only exception is if I send something not a
multiple of three
 bytes but terminate the transfer with 0xf7, it will send
 everything including the 0xf7 - but this kills the sysex transfer. 
 _Every_ SysEx message must be terminated with F7. 
 The CZ1000 expects seven bytes to start the sysex transfer, at which
 point it will reply with a message and wait for an acknowledge.  The
 the PC should start to send the patch data, but it's quite important
 not to send that too soon otherwise the CZ will misbehave in various
 interesting ways.  Once all the patch data is send - with breaks for
 acks in between - the final 0xf7 is sent to terminate the sysex dump. 
So the messages used by the CZ1000 in this protocol are not actually
MIDI messages.

...
    Is it really impossible to just send raw bytes over a
USB MIDI cable? 
 It is possible to send MIDI messages over a USB MIDI cable. 
 According to the USB MIDI spec there is an event packet to send just
 single bytes. 
There are devices that do not support this single-byte packet.

...
  This isn't implemented in the kernel, 
It's used for real-time messages.

...
  it would be incredibly handy for sysex transfers,
debugging and the
 like.

 Perhaps the answer is just to ditch alsa and poke the USB device with
 libusb? 
Or change the driver to always use single-byte packets (modify the first
"if" in snd_usbmidi_transmit_byte).

...
  With a bit of testing, I've determined that at
least the USB
 interfaces I have at hand do not support sysex.  They will pass some
 interestingly "interpreted" version of sysex, which is of course
 corrupted and unreadable by the device. 
In what way corrupted?

Regards,
Clemens

Re: [LAD] Weird USB MIDI sysex problem