Re: [linux-audio-dev] Basic MIDI question

On Wed, 26 Jul 2006, Clemens Ladisch wrote:

> Ari Kauppi wrote:
>> On Wed, 26 Jul 2006, Jens M Andreasen wrote:
>>
>>> if(runningStatus == NOTE_ON || runningStatus == NOTE_OFF)
>>
>> If you plan to receive messages from other channels than 0 you have to
>> use (runningStatus & 0xF0) instead of the full runningStatus and perhaps
>> check for (runningStaus & 0x0F) == receiveChannel..
>
> Okay, here is my entry to the Official LAD MIDI Parser Contest 2006:

Good try but it still has at least one potential problem: according to
MIDI spec running status should be set only with channel messages.
Sysex/common messages should reset it to undefined (0).

With this exact implementation it shouldn't cause any problems but if the
parser is extended/modified later it might become a pretty hard to find
bug with some input..

> void handleByte(u8 byte)
> {
> /* in a driver, these static variables should go into some struct: */
> static enum {
> STATE_UNKNOWN, /* not a note command */
> STATE_NOTE1, /* expecting 1st data byte (note) */
> STATE_NOTE2, /* expecting 2nd data byte (velocity) */
> } state = STATE_UNKNOWN;
> static u8 command;
> static u8 note;
>
> if (byte >= 0xf8) /* real-time command */
> ;
> else if (byte & 0x80) { /* status byte */
> command = byte;
> /* note-on or note-off? */
> state = (byte & 0xf0) <= 0x90 ? STATE_NOTE1 : STATE_UNKNOWN;
> } else { /* data byte */
> if (state == STATE_NOTE1) {
> note = byte;
> state = STATE_NOTE2;
> } else if (state == STATE_NOTE2) {
> if ((command & 0xf0) == 0x90 && byte > 0) {
> /* note on */
> } else {
> /* note off */
> }
> state = STATE_NOTE1;
> }
> }
> }

-- 
Ari