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|
;---------------------------------------------------------------------------;
; Software implemented UART module ;
; (C)ChaN, 2005 (http://elm-chan.org/) ;
;---------------------------------------------------------------------------;
; Bit rate settings:
;
; 1MHz 2MHz 4MHz 6MHz 8MHz 10MHz 12MHz 16MHz 20MHz
; 2.4kbps 138 - - - - - - - -
; 4.8kbps 68 138 - - - - - - -
; 9.6kbps 33 68 138 208 - - - - -
; 19.2kbps - 33 68 102 138 173 208 - -
; 38.4kbps - - 33 50 68 85 102 138 172
; 57.6kbps - - 21 33 44 56 68 91 114
; 115.2kbps - - - - 21 27 33 44 56
.nolist
#include <avr/io.h>
.list
#define BPS 102 /* Bit delay. (see above table) */
#define BIDIR 0 /* 0:Separated Tx/Rx, 1:Shared Tx/Rx */
#define OUT_1 sbi _SFR_IO_ADDR(SUART_OUT_PORT), SUART_OUT_BIT /* Output 1 */
#define OUT_0 cbi _SFR_IO_ADDR(SUART_OUT_PORT), SUART_OUT_BIT /* Output 0 */
#define SKIP_IN_1 sbis _SFR_IO_ADDR(SUART_IN_PIN), SUART_IN_BIT /* Skip if 1 */
#define SKIP_IN_0 sbic _SFR_IO_ADDR(SUART_IN_PIN), SUART_IN_BIT /* Skip if 0 */
#ifdef SPM_PAGESIZE
.macro _LPMI reg
lpm \reg, Z+
.endm
.macro _MOVW dh,dl, sh,sl
movw \dl, \sl
.endm
#else
.macro _LPMI reg
lpm
mov \reg, r0
adiw ZL, 1
.endm
.macro _MOVW dh,dl, sh,sl
mov \dl, \sl
mov \dh, \sh
.endm
#endif
;---------------------------------------------------------------------------;
; Transmit a byte in serial format of N81
;
;Prototype: void xmit (uint8_t data);
;Size: 16 words
.global xmit
.func xmit
xmit:
#if BIDIR
ldi r23, BPS-1 ;Pre-idle time for bidirectional data line
5: dec r23 ;
brne 5b ;/
#endif
in r0, _SFR_IO_ADDR(SREG) ;Save flags
com r24 ;C = start bit
ldi r25, 10 ;Bit counter
cli ;Start critical section
1: ldi r23, BPS-1 ;----- Bit transferring loop
2: dec r23 ;Wait for a bit time
brne 2b ;/
brcs 3f ;MISO = bit to be sent
OUT_1 ;
3: brcc 4f ;
OUT_0 ;/
4: lsr r24 ;Get next bit into C
dec r25 ;All bits sent?
brne 1b ; no, coutinue
out _SFR_IO_ADDR(SREG), r0 ;End of critical section
ret
.endfunc
;---------------------------------------------------------------------------;
; Receive a byte
;
;Prototype: uint8_t rcvr (void);
;Size: 19 words
.global rcvr
.func rcvr
rcvr:
in r0, _SFR_IO_ADDR(SREG) ;Save flags
ldi r24, 0x80 ;Receiving shift reg
cli ;Start critical section
1: SKIP_IN_1 ;Wait for idle
rjmp 1b
2: SKIP_IN_0 ;Wait for start bit
rjmp 2b
ldi r25, BPS/2 ;Wait for half bit time
3: dec r25
brne 3b
4: ldi r25, BPS ;----- Bit receiving loop
5: dec r25 ;Wait for a bit time
brne 5b ;/
lsr r24 ;Next bit
SKIP_IN_0 ;Get a data bit into r24.7
ori r24, 0x80
brcc 4b ;All bits received? no, continue
out _SFR_IO_ADDR(SREG), r0 ;End of critical section
ret
.endfunc
; Not wait for start bit. This should be called after detecting start bit.
.global recv
.func recv
recv:
in r0, _SFR_IO_ADDR(SREG) ;Save flags
ldi r24, 0x80 ;Receiving shift reg
cli ;Start critical section
;1: SKIP_IN_1 ;Wait for idle
; rjmp 1b
;2: SKIP_IN_0 ;Wait for start bit
; rjmp 2b
ldi r25, BPS/2 ;Wait for half bit time
3: dec r25
brne 3b
4: ldi r25, BPS ;----- Bit receiving loop
5: dec r25 ;Wait for a bit time
brne 5b ;/
lsr r24 ;Next bit
SKIP_IN_0 ;Get a data bit into r24.7
ori r24, 0x80
brcc 4b ;All bits received? no, continue
ldi r25, BPS/2 ;Wait for half bit time
6: dec r25
brne 6b
7: SKIP_IN_1 ;Wait for stop bit
rjmp 7b
out _SFR_IO_ADDR(SREG), r0 ;End of critical section
ret
.endfunc
|
