Sending SysEx MIDI messages

[Dan Kersten]

Hi,

I am trying to send and receive MIDI SysEx messages and I can receive
them fine, but I am having trouble sending.

Basically, I'm not really sure how to go about sending them. I tried
passing a byte buffer for LUFA to send, but that did not work (I did
not receive anything on the other end). I tried splitting the message
in the same way that the input messages are split when they arrive
(eg, 1, 2 or 3 byte packets + command byte), but that didn't work for
me either.

Any tips, help or pointers to documentation would be greatly
appreciated!

Thanks,
Dan.

[Robin Green]

USB-MIDI is a little different than straight MIDI. You need to package
your MIDI stream into 4-byte packets for transmission over USB. As
most MIDI messages are 3 bytes you simply add a header byte that tells
the USB system which "virtual device" this MIDI is coming from but as
SYSEX messages are a variable number of bytes you need to use the 1-,
2- and 3-byte message packets to assemble a stream of USB packets from
your SYSEX stream. Table 4.1 in the MIDI-USB standard shows you the
list of available packets:

http://www.usb.org/developers/devclass_docs/midi10.pdf

Packets 4,5,6 and 7 are the ones you need. Examples of SYSEX are on table 4.2.

In fact, read the whole document. It explains a lot about the
paramaters that LUFA uses to construct USB packets and also points out
the large implementation holes in the sender and parser that I haven't
gotten around to filling yet with code yet...

- Robin Green.

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[Dan Kersten]

Hi Robin,

Perfect! Thanks, that explains it alright. I didn't realize that USB-
MIDI was handled a little differently.

Thanks for the help.
Dan.

[Xulio Coira]

Hi Dan,

Here is some code I wrote in order to send SYSEX messages with LUFA, in case you find it useful.

http://pastebin.com/vdFLiWb0

BR,

Xulio.

[Robin Green]

Beautiful code, man. Really clear.

- Robin Green

To view this discussion on the web visit https://groups.google.com/d/msg/lufa-support/-/in1oGPPqapAJ.

[Donald Delmar Davis]

now on to the sysex bootloader.....

[Dean Camera]

Xulio, well done, that's damned near poetry in code - as Robin says, very clean.

I remember discussing making a MIDI class bootloader with Feurig a while back and even started an implementation, but gave up when I couldn't figure out the best way to make a host-side application to drive it. Perhaps I should look into that again.

- Dean

[Xulio Coira]

Hi Dean,

I've also in my mind a MIDI firmware update procedure, using SYSEX, but not using MIDI class bootloader.

I would send firmware image using SYSEX, save to flash, and then the DFU bootloader detect and flash it, but it's only in my mind by now :)

Sorry for my ignorance, but why a MIDI class bottloader could be useful?

Regards,

Xulio.

[Donald Delmar Davis]

Midi is setup up for in band software updates (really one of the bigger reasons for sysex). 

You can upload and run new code without ever leaving the class.   The client side is really kind of the painful part. 

I wrote a protocol a few years back called (lets get loaded) and started a python based loader for it. 

I will see if enough of it is fleshed out to make a spec. 

To view this discussion on the web visit https://groups.google.com/d/msg/lufa-support/-/klA4zUFUAXYJ.

[Dean Camera]

It's also driver-less on many systems - I've been wondering if it would be possible to encode firmware into an actual MIDI file, and then play that to the device to download new code. That would allow for software-less upgrades on the client side. If nothing else, it's another option people can choose if they wish.

Donald: if you can cook up a front-end for it, I can make the bootloader if you don't want to do it.

- Dean

[Sebastian Steppeler]

This would be perfectly possible! You'd just use e.g. note on messages and encode a nibble in the note number and the other one in the velocity. You could then always create note on and note off blocks to obey the midi protocol - just to be sure nothing weird happens.

Of course you could also use sysex messages, but I don't know if every player will pass them on unchanged...

regards,

Sebastian

2012/8/13 Dean Camera <abcmi...@gmail.com>

To view this discussion on the web visit https://groups.google.com/d/msg/lufa-support/-/vrtIKZe0xM8J.