MIDI-IN2

10 REM > MIDI-IN2

20 REM Redirect incoming MIDI to SOUND

30 :

40 REM Note: Even though the MIDI port is being read in machine code,

50 REM the BASIC code that calls it runs too slow, so after a while

60 REM data bytes get dropped, and subsequent bytes are read in the

70 REM wrong order, reading byte 2 of command 1 followed by byte 1 of

80 REM then next command.

90 :

100 REM The conventional method of doing MIDI input like this is that

110 REM the MIDI input is read by a background interupt handler that

120 REM fills a buffer, and the foreground polls and reads from the

130 REM buffer - similar to the serial input buffer.

140 :

150 REM Alternatively, a common method is that the MIDI input is read

160 REM in a fast machine code loop in the /foreground/ and the input

170 REM processing is done in the /background/ - the opposite way to

180 REM normal.

190 :

200 DIM mcode% 100

210 mCtrl=&FCF0

220 mData=mCtrl+1

230 FOR I%=0 TO 1

240 P%=mcode%

250 [OPT I%*3

260 LDY command :\ Y is current command

270 .loop1

280 BIT &FF:BMI esc

290 LDA mCtrl:AND #1:BEQ loop1 :\ Wait for byte

300 LDA mData :\ Get byte

310 BPL TestCommand :\ Data byte, use current command

320 .readcommand

330 CMP #&F0:BCS loop1 :\ Ignore system commands

340 TAY :\ Make this the current command byte

350 .waitfor1

360 BIT &FF:BMI esc

370 LDA mCtrl:AND #1:BEQ waitfor1 :\ Wait for first data byte

380 LDA mData:BMI readcommand :\ Another command, loop back

390 .TestCommand

400 TAX :\ First data byte

410 CPY #&E0:BCS waitfor2 :\ &Ex has two data bytes

420 CPY #&C0:BCS nomore :\ &Cx-&Dx has one data byte

430 :\ &8x-&Bx has two data bytes

440 .waitfor2

450 BIT &FF:BMI esc

460 LDA mCtrl:AND #1:BEQ waitfor2 :\ Wait for a byte

470 LDA mData:BMI readcommand :\ Get second data byte

480 \ Y=command, X=1st data byte, A=2nd data byte

490 \ or Y=command, X=only data byte

500 .nomore

510 STA byte2

520 STX byte1

530 STY command

540 TYA

550 .esc

560 RTS

570 .command:BRK

580 .byte1:BRK

590 .byte2:BRK

600 ]

610 NEXT I%

620 :

630 REM Demo code

640 ?mCtrl=&03:REM Reset

650 ?mCtrl=&16:REM Set clock speed

660 ?command=&90 :REM Set current command to 'note on'

670 REPEAT

680 cmd%=(USR(mcode%))AND&F0 :REM Wait for command

690 PRINT ?command, ?byte1, ?byte2

700 IF cmd%=&90:SOUND &11,-10 AND (?byte2>0),?byte1*4-138,20 :REM Note On

710 IF cmd%=&80:SOUND &11,0,0,0 :REM Note Off

720 UNTIL FALSE