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dbg_putchar.c
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dbg_putchar.c
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/*
* ----------------------------------------------------------------------------
* "THE BEER-WARE LICENSE" (Revision 42, by Joerg Wunsch):
* <dinuxbg .at. gmail.com> wrote this file. As long as you retain this notice
* you can do whatever you want with this stuff. If we meet some day, and you
* think this stuff is worth it, you can buy me a beer in return.
* Dimitar Dimitrov
* ----------------------------------------------------------------------------
*/
#include <stdint.h>
#include <avr/io.h>
#include <avr/interrupt.h>
#include "dbg_putchar.h"
#if DBG_UART_ENABLE
void dbg_putchar(uint8_t c)
{
#define DBG_UART_TX_NUM_DELAY_CYCLES ((F_CPU/DBG_UART_BAUDRATE-16)/4+1)
#define DBG_UART_TX_NUM_ADD_NOP ((F_CPU/DBG_UART_BAUDRATE-16)%4)
uint8_t sreg;
uint16_t tmp;
uint8_t numiter = 10;
sreg = SREG;
cli();
asm volatile (
/* put the START bit */
"in %A0, %3" "\n\t" /* 1 */
"cbr %A0, %4" "\n\t" /* 1 */
"out %3, %A0" "\n\t" /* 1 */
/* compensate for the delay induced by the loop for the
* other bits */
"nop" "\n\t" /* 1 */
"nop" "\n\t" /* 1 */
"nop" "\n\t" /* 1 */
"nop" "\n\t" /* 1 */
"nop" "\n\t" /* 1 */
/* delay */
"1:" "ldi %A0, lo8(%5)" "\n\t" /* 1 */
"ldi %B0, hi8(%5)" "\n\t" /* 1 */
"2:" "sbiw %A0, 1" "\n\t" /* 2 */
"brne 2b" "\n\t" /* 1 if EQ, 2 if NEQ */
#if DBG_UART_TX_NUM_ADD_NOP > 0
"nop" "\n\t" /* 1 */
#if DBG_UART_TX_NUM_ADD_NOP > 1
"nop" "\n\t" /* 1 */
#if DBG_UART_TX_NUM_ADD_NOP > 2
"nop" "\n\t" /* 1 */
#endif
#endif
#endif
/* put data or stop bit */
"in %A0, %3" "\n\t" /* 1 */
"sbrc %1, 0" "\n\t" /* 1 if false,2 otherwise */
"sbr %A0, %4" "\n\t" /* 1 */
"sbrs %1, 0" "\n\t" /* 1 if false,2 otherwise */
"cbr %A0, %4" "\n\t" /* 1 */
"out %3, %A0" "\n\t" /* 1 */
/* shift data, putting a stop bit at the empty location */
"sec" "\n\t" /* 1 */
"ror %1" "\n\t" /* 1 */
/* loop 10 times */
"dec %2" "\n\t" /* 1 */
"brne 1b" "\n\t" /* 1 if EQ, 2 if NEQ */
: "=&w" (tmp), /* scratch register */
"=r" (c), /* we modify the data byte */
"=r" (numiter) /* we modify number of iter.*/
: "I" (_SFR_IO_ADDR(DBG_UART_TX_PORT)),
"M" (1<<DBG_UART_TX_PIN),
"i" (DBG_UART_TX_NUM_DELAY_CYCLES),
"1" (c), /* data */
"2" (numiter)
);
SREG = sreg;
}
#undef DBG_UART_TX_NUM_DELAY_CYCLES
#undef DBG_UART_TX_NUM_ADD_NOP
#endif