==== MIDI ====

Here is an example of code that will allow the MICrODEC to receive MIDI data over the serial port.  Because of the way interrupts are handled, it is difficult to have a generic MIDI interface in the Main loop which communicates with the Function programs.  It is possible to do this, but it would cut down on the processing time within the Function programs.  Therefore, to accommodate MIDI, each Function must have its own implementation.  This has the net effect of maximizing processing time, program by program.

== Initialize the USART

This first section of code is an initialization routine for talking MIDI, and must be placed at the beginning of the Function program.  This sets up the USART for the 31.25kbps data transfer rate, and sets the start bits and stop bits.

{{{#!highlight nasm
; initialize USART for midi transfer and new jump address
ldi r30,$0f ; set new jump address
            ; this value will need to be changed if there is more
            ; initialization code that follows the USART
            ; initialization.     
ldi r17,$00
sts ucsr0a,r17 ; set USART to single speed
sts ubrr0h,r17 ; set USART to 31.25kbps baud rate for midi
ldi r17,$27
sts ubrr0l,r17
ldi r17,$06
sts ucsr0c,r17 ; set USART to 8 bit mode
ldi r17,$10
sts ucsr0b,r17 ; turn on USART reciever
}}}



{{{#!highlight nasm
; get delay settings
lds r17,ucsr0a ; get USART control register
sbrs r17,rxc0 ; check if byte has been recieved
rjmp shift_000023 ; skip buffer read
lds r17,udr0 ; get data byte
brts update_000023 ; skip if command byte already recieved
andi r17,$f0 ; mask off channel number - recieve all channels for now
cpi r17,$b0 ; check if controller
brne shift_000023 ; do nothing if not correct command byte
set ; set t register to indicate correct command byte recieved
rjmp shift_000023 ; finish off

update_000023: ; update delay time with pitch bend value

sbrc r17,$07 ; check if msb is set - command byte
rjmp resetusart_000023 ; dont process data if command byte
tst r14 ; check if first byte
brne secondbyte_000023 ; skip to second byte if not
cpi r17,$47 ; check if controller number 71
brne resetusart_000023
inc r14 ; set byte counter to first byte recieved
rjmp shift_000023 ; finish off

secondbyte_000023: ; get second byte

lsl r17 ; shift 14b number to 16b number
;lsl r0
;rol r17
mov r27,r17 ; move data to desired delay register
;mov r26,r0
cpi r27,$03 ; check if desired delay is less than 9ms
brsh resetusart_000023 ; finish off if delay time is greater than 9ms
ldi r27,$03 ; set desired delay to 9ms
clr r26

resetusart_000023: ; reset usart

clt ; reset command byte indicator
clr r14 ; reset byte counter
}}}