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← Revision 6 as of 2010-08-14 02:57:47
Size: 2742
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← Revision 7 as of 2010-08-14 03:19:11 →
Size: 3739
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| Deletions are marked like this. | Additions are marked like this. |
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sts ucsr0a,r17 ; set USART to single speed sts ubrr0h,r17 ; set USART to 31.25kbps baud rate for midi |
sts UCSR0A,r17 ; set USART to single speed sts UBRR0H,r17 ; set USART to 31.25kbps baud rate for midi |
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| sts ubrr0l,r17 | sts UBRR0L,r17 |
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| sts ucsr0c,r17 ; set USART to 8 bit mode | sts UCSR0C,r17 ; set USART to 8 bit mode |
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| sts ucsr0b,r17 ; turn on USART reciever | sts UCSR0B,r17 ; turn on USART reciever |
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| ===== Receive Data from the USART ===== | |
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| This code only shows how to receive data from the USART, although transmitting data would be much simpler. The first thing that happens is that the code checks to see if any USART data has arrived, and if it has, it checks for a MIDI command byte. If a MIDI command byte is received, it then checks for a MIDI data byte. After it receives the data, it updates a register that the Function program accesses to modify a parameter. It then resets itself to wait for another MIDI command byte. This code is run each sample period. | |
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; 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 |
; receive MIDI data lds r17,UCSR0A ; get USART control register sbrs r17,RXC0 ; check if byte has been received rjmp done_UID ; finish off if no byte has been received lds r17,UDR0 ; get data byte if one arrived brts update_UID ; skip if command byte already received ; the t-bit is used to indicate a command byte recieved ; although another bit in a register could also be used andi r17,$f0 ; mask off channel number - receive all channels for now ; this can be set to look for a particular MIDI channel cpi r17,$b0 ; check if appropriate MIDI command number ; can be set to any MIDI command brne done_UID ; do nothing if not correct command byte set ; set t register to indicate correct command byte received rjmp done_UID ; finish off |
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| update_000023: ; update delay time with pitch bend value | update_UID: ; update data register with MIDI data |
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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 |
sbrc r17,$07 ; check if msb is set - indicates command byte ; if command byte is received at this point, it is out ; of sequence, and the program should reset itself rjmp resetusart_UID ; dont process data if command byte tst r14 ; check if first byte - r14 holds the byte counter (0 = first byte) brne secondbyte_UID ; skip to second byte if not cpi r17,$47 ; if first byte, check if controller number 71 ; can be set to any controller number brne resetusart_UID ; do not process data if not the correct controller inc r14 ; set byte counter to first byte received rjmp done_UID ; finish off |
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| secondbyte_000023: ; get second byte | secondbyte_UID: ; get second byte |
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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 |
mov r27,r17 ; move MIDI data to register that the Function program ; references |
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| resetusart_000023: ; reset usart | resetusart_UID: ; reset usart |
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done_UID: ; place for rest of program |
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.
1 ; initialize USART for midi transfer and new jump address
2 ldi r30,$0f ; set new jump address
3 ; this value will need to be changed if there is more
4 ; initialization code that follows the USART
5 ; initialization.
6 ldi r17,$00
7 sts UCSR0A,r17 ; set USART to single speed
8 sts UBRR0H,r17 ; set USART to 31.25kbps baud rate for midi
9 ldi r17,$27
10 sts UBRR0L,r17
11 ldi r17,$06
12 sts UCSR0C,r17 ; set USART to 8 bit mode
13 ldi r17,$10
14 sts UCSR0B,r17 ; turn on USART reciever
15
Receive Data from the USART
This code only shows how to receive data from the USART, although transmitting data would be much simpler. The first thing that happens is that the code checks to see if any USART data has arrived, and if it has, it checks for a MIDI command byte. If a MIDI command byte is received, it then checks for a MIDI data byte. After it receives the data, it updates a register that the Function program accesses to modify a parameter. It then resets itself to wait for another MIDI command byte. This code is run each sample period.
1 ; receive MIDI data
2 lds r17,UCSR0A ; get USART control register
3 sbrs r17,RXC0 ; check if byte has been received
4 rjmp done_UID ; finish off if no byte has been received
5 lds r17,UDR0 ; get data byte if one arrived
6 brts update_UID ; skip if command byte already received
7 ; the t-bit is used to indicate a command byte recieved
8 ; although another bit in a register could also be used
9 andi r17,$f0 ; mask off channel number - receive all channels for now
10 ; this can be set to look for a particular MIDI channel
11 cpi r17,$b0 ; check if appropriate MIDI command number
12 ; can be set to any MIDI command
13 brne done_UID ; do nothing if not correct command byte
14 set ; set t register to indicate correct command byte received
15 rjmp done_UID ; finish off
16
17 update_UID: ; update data register with MIDI data
18
19 sbrc r17,$07 ; check if msb is set - indicates command byte
20 ; if command byte is received at this point, it is out
21 ; of sequence, and the program should reset itself
22 rjmp resetusart_UID ; dont process data if command byte
23 tst r14 ; check if first byte - r14 holds the byte counter (0 = first byte)
24 brne secondbyte_UID ; skip to second byte if not
25 cpi r17,$47 ; if first byte, check if controller number 71
26 ; can be set to any controller number
27 brne resetusart_UID ; do not process data if not the correct controller
28 inc r14 ; set byte counter to first byte received
29 rjmp done_UID ; finish off
30
31 secondbyte_UID: ; get second byte
32
33 mov r27,r17 ; move MIDI data to register that the Function program
34 ; references
35
36 resetusart_UID: ; reset usart
37
38 clt ; reset command byte indicator
39 clr r14 ; reset byte counter
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41 done_UID: ; place for rest of program
42