/
soft_uart.S
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/
soft_uart.S
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/*
* Copyright (c) 2016, Alex Taradov <alex@taradov.com>
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are met:
*
* 1. Redistributions of source code must retain the above copyright notice,
* this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
* 3. The name of the author may not be used to endorse or promote products
* derived from this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
* LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
* POSSIBILITY OF SUCH DAMAGE.
*/
/*- Includes ----------------------------------------------------------------*/
#include <avr/io.h>
/*- Definitions -------------------------------------------------------------*/
#define PROBE_PORT _SFR_IO_ADDR(PINB)
#define PROBE_PIN 4
#define BAUDRATE 38400
#define HALF_BIT (((F_CPU / BAUDRATE) / (4 * 2)) - 2)
#define TMP r18
#define CNT r19
#define BIT r20
#define BYTE r24
#define RETURN r24
/*- Implementations ---------------------------------------------------------*/
.text
//-----------------------------------------------------------------------------
.type delay_half_bit, @function
delay_half_bit:
ldi TMP, HALF_BIT
1: dec TMP
nop
brne 1b
ret
.size delay_half_bit, .-delay_half_bit
//-----------------------------------------------------------------------------
.type sample_bit, @function
sample_bit:
clc
ror BYTE
sbic PROBE_PORT, PROBE_PIN
ori BYTE, 0x80
ret
.size sample_bit, .-sample_bit
//-----------------------------------------------------------------------------
.global uart_sync
.type uart_sync, @function
uart_sync:
ldi RETURN, 0
ldi CNT, 0xff
10:
sbic PROBE_PORT, PROBE_PIN
rjmp 20f
dec CNT
brne 10b
ret
20:
sbis PROBE_PORT, PROBE_PIN
rjmp 30f
dec CNT
brne 20b
ret
30:
rcall delay_half_bit
sbic PROBE_PORT, PROBE_PIN
rjmp 40f
rcall delay_half_bit
sbic PROBE_PORT, PROBE_PIN
rjmp 40f
rcall delay_half_bit
sbic PROBE_PORT, PROBE_PIN
rjmp 40f
rcall delay_half_bit
rcall delay_half_bit
sbis PROBE_PORT, PROBE_PIN
rjmp 40f
//sbi _SFR_IO_ADDR(PORTB), 3
//cbi _SFR_IO_ADDR(PORTB), 3
ldi RETURN, 1
40:
ret
.size uart_sync, .-uart_sync
//-----------------------------------------------------------------------------
.global uart_rx
.type uart_rx, @function
uart_rx:
10:
sbis PROBE_PORT, PROBE_PIN
rjmp 10b
20:
sbic PROBE_PORT, PROBE_PIN
rjmp 20b
//sbi _SFR_IO_ADDR(PORTB), 3
ldi BIT, 8
rcall delay_half_bit
30:
rcall delay_half_bit
rcall delay_half_bit
rcall sample_bit
dec BIT
brne 30b
//cbi _SFR_IO_ADDR(PORTB), 3
ret
.size uart_rx, .-uart_rx
//-----------------------------------------------------------------------------
.global uart_wait_rx
.type uart_wait_rx, @function
uart_wait_rx:
ldi RETURN, 0
ldi CNT, 0xff
10:
sbis PROBE_PORT, PROBE_PIN
rjmp 20f
dec CNT
brne 10b
ret
20:
ldi BIT, 8
rcall delay_half_bit
30:
rcall delay_half_bit
rcall delay_half_bit
rcall sample_bit
dec BIT
brne 30b
40:
sbis PROBE_PORT, PROBE_PIN
rjmp 40b
ret
.size uart_wait_rx, .-uart_wait_rx