Hans,

Very good analysis. A 12 MHz 8051 is more than able to handle a MIDI interface if written "tightly". I usually allow myself a little headroom and use 24MHz when i can, however.

I also think "message framing" should not occur in the interrupt routine. The single byte MIDI clock should occur in the interrupt but everything else is fine pouring into a buffer.

I have written many MIDI xfaces and found buffering the data to be the best solution when faced with the variety of MIDI data that can occur expecially SysEx Messages.

Unless you are writing a solution for one specific MIDI Device i find, if a trick exists for interfacing to MIDI, it is the message "mix" that will get you.

While a buffer indicates you are out of real-time in fact if you have other things to do that are interrupt driven (and are also short) the buffer neatly relieves "pressure" on the cpu and only micro-seconds of delays result.

I do have the tendancy to drop active sensing as the MIDI to Control Voltage interfaces, DCO's and Control Surfaces i make don't really use these messages.

Also another note, i use '8051 variants regularly to handle audio processing.

regards,
p