Points of Interest

This weekend I have written some code to deal with MIDI system exclusive data. Primarly I wanted to create a graphical tool to do backups of the memory contents of my synthesizers. There are some tools available for Mac OS X and Windows, but there was none for Linux. So I had written SimpleSysexxer back in 2006, but it has some bugs and its backend code is rather experimental. So I removed all backend code from it and started from scratch.

I am still using the famous RtMidi classes written by Gary P. Scavone, which simplify the communication with the underlaying ALSA API a lot.

While coding and testing, I noticed that I get errors when sending certain test data. It turned out that this happens if the file size exceeds 16355 bytes. Unfortunately, I have at least two devices which produce such SysEx data. To ensure the error was not caused by some malformed files, I have created two example files. Both start with an 0xF0 byte and end with an 0xF7 byte, both sufficient to identify it as SysEx data on the MIDI bus. All the rest are just 0x00 bytes. One file is exactly 16355 bytes in size, the other one is exactly 16356 bytes. The first one can be sent, the second one causes an error.

I hope to get some help of the Linux Audio developer community concerning this issue, as I am not yet familiar enough with the ALSA API. I hope there is a coding workaround, because otherwise it needed patching, compiling and installing a custom Linux kernel. Not a problem during the cold and dark winter months. But hey, it’s summertime :) .

This entry was posted on Monday, July 27th, 2009 at 0:59 and is filed under Musical Instruments, Products, Software. You can follow any responses to this entry through the RSS 2.0 feed. Both comments and pings are currently closed.