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i2cmaster.S
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;*************************************************************************
; Title : I2C (Single) Master Implementation
; Author: Peter Fleury <pfleury@gmx.ch>
; based on Atmel Appl. Note AVR300
; File: $Id: i2cmaster.S,v 1.13 2015/09/16 11:21:00 peter Exp $
; Software: AVR-GCC 4.x
; Target: any AVR device
;
; DESCRIPTION
; Basic routines for communicating with I2C slave devices. This
; "single" master implementation is limited to one bus master on the
; I2C bus.
;
; Based on the Atmel Application Note AVR300, corrected and adapted
; to GNU assembler and AVR-GCC C call interface
; Replaced the incorrect quarter period delays found in AVR300 with
; half period delays.
;
; USAGE
; These routines can be called from C, refere to file i2cmaster.h.
; See example test_i2cmaster.c
; Adapt the SCL and SDA port and pin definitions and eventually
; the delay routine to your target !
; Use 4.7k pull-up resistor on the SDA and SCL pin.
;
; NOTES
; The I2C routines can be called either from non-interrupt or
; interrupt routines, not both.
;
;*************************************************************************
#include <avr/io.h>
#undef SCL_PORT
#undef SCL_DDR
;******----- Adapt these SCA and SCL port and pin definition to your target !!
;
#define SDA 4 // SDA Port D, Pin 4
#define SCL 5 // SCL Port D, Pin 5
#define SDA_PORT PORTD // SDA Port D
#define SCL_PORT PORTD // SCL Port D
;******----------------------------------------------------------------------
;-- map the IO register back into the IO address space
#define SDA_DDR (_SFR_IO_ADDR(SDA_PORT) - 1)
#define SCL_DDR (_SFR_IO_ADDR(SCL_PORT) - 1)
#define SDA_OUT _SFR_IO_ADDR(SDA_PORT)
#define SCL_OUT _SFR_IO_ADDR(SCL_PORT)
#define SDA_IN (_SFR_IO_ADDR(SDA_PORT) - 2)
#define SCL_IN (_SFR_IO_ADDR(SCL_PORT) - 2)
#ifndef __tmp_reg__
#define __tmp_reg__ 0
#endif
.section .text
;*************************************************************************
; delay half period
; For I2C in normal mode (100kHz), use T/2 > 5us
; For I2C in fast mode (400kHz), use T/2 > 1.25us
;*************************************************************************
.stabs "",100,0,0,i2c_delay_T2
.stabs "i2cmaster.S",100,0,0,i2c_delay_T2
.func i2c_delay_T2 ; delay 5.0 microsec with 4 Mhz crystal
i2c_delay_T2: ; 3 cycles
#if F_CPU <= 4000000UL
rjmp 1f ; 2 "
1: rjmp 2f ; 2 "
2: rjmp 3f ; 2 "
3: rjmp 4f ; 2 "
4: rjmp 5f ; 2 "
5: rjmp 6f ; 2 "
6: nop ; 1 "
ret ; 4 " total 20 cyles = 5.0 microsec with 4 Mhz crystal
#elif F_CPU <= 8000000UL
push r24 ; 2 cycle
ldi r24, 7 ; 1 cycle
nop ; 1 cycle
1: sbiw r24, 1 ; 2 cycle
brne 1b ; 2 or 1 cycle, 4 cycles per loop
pop r24 ; 2 ycle
ret ; 4 cycle = total 60 cycles = 5.0 microsec with 12 Mhz crystal
#elif F_CPU <= 12000000UL
push r24 ; 2 cycle
ldi r24, 12 ; 1 cycle
nop ; 1 cycle
1: sbiw r24, 1 ; 2 cycle
brne 1b ; 2 or 1 cycle, 4 cycles per loop
pop r24 ; 2 ycle
ret ; 4 cycle = total 60 cycles = 5.0 microsec with 12 Mhz crystal
#elif F_CPU <= 16000000UL
push r24 ; 2 cycle
ldi r24, 17 ; 1 cycle
nop ; 1 cycle
1: sbiw r24, 1 ; 2 cycle
brne 1b ; 2 or 1 cycle, 4 cycles per loop
pop r24 ; 2 ycle
ret ; 4 cycle = total 80 cycles = 5.0 microsec with 16 Mhz crystal
#else
push r24 ; 2 cycle
ldi r24, 22 ; 1 cycle
nop ; 1 cycle
1: sbiw r24, 1 ; 2 cycle
brne 1b ; 2 or 1 cycle, 4 cycles per loop
pop r24 ; 2 ycle
ret ; 4 cycle = total 100 cycles = 5.0 microsec with 20 Mhz crystal
#endif
.endfunc ;
;*************************************************************************
; Initialization of the I2C bus interface. Need to be called only once
;
; extern void i2c_init(void)
;*************************************************************************
.global i2c_init
.func i2c_init
i2c_init:
cbi SDA_DDR,SDA ;release SDA
cbi SCL_DDR,SCL ;release SCL
cbi SDA_OUT,SDA
cbi SCL_OUT,SCL
ret
.endfunc
;*************************************************************************
; Issues a start condition and sends address and transfer direction.
; return 0 = device accessible, 1= failed to access device
;
; extern unsigned char i2c_start(unsigned char addr);
; addr = r24, return = r25(=0):r24
;*************************************************************************
.global i2c_start
.func i2c_start
i2c_start:
sbi SDA_DDR,SDA ;force SDA low
rcall i2c_delay_T2 ;delay T/2
rcall i2c_write ;write address
ret
.endfunc
;*************************************************************************
; Issues a repeated start condition and sends address and transfer direction.
; return 0 = device accessible, 1= failed to access device
;
; extern unsigned char i2c_rep_start(unsigned char addr);
; addr = r24, return = r25(=0):r24
;*************************************************************************
.global i2c_rep_start
.func i2c_rep_start
i2c_rep_start:
sbi SCL_DDR,SCL ;force SCL low
rcall i2c_delay_T2 ;delay T/2
cbi SDA_DDR,SDA ;release SDA
rcall i2c_delay_T2 ;delay T/2
cbi SCL_DDR,SCL ;release SCL
rcall i2c_delay_T2 ;delay T/2
sbi SDA_DDR,SDA ;force SDA low
rcall i2c_delay_T2 ;delay T/2
rcall i2c_write ;write address
ret
.endfunc
;*************************************************************************
; Issues a start condition and sends address and transfer direction.
; If device is busy, use ack polling to wait until device is ready
;
; extern void i2c_start_wait(unsigned char addr);
; addr = r24
;*************************************************************************
.global i2c_start_wait
.func i2c_start_wait
i2c_start_wait:
mov __tmp_reg__,r24
i2c_start_wait1:
sbi SDA_DDR,SDA ;force SDA low
rcall i2c_delay_T2 ;delay T/2
mov r24,__tmp_reg__
rcall i2c_write ;write address
tst r24 ;if device not busy -> done
breq i2c_start_wait_done
rcall i2c_stop ;terminate write operation
rjmp i2c_start_wait1 ;device busy, poll ack again
i2c_start_wait_done:
ret
.endfunc
;*************************************************************************
; Terminates the data transfer and releases the I2C bus
;
; extern void i2c_stop(void)
;*************************************************************************
.global i2c_stop
.func i2c_stop
i2c_stop:
sbi SCL_DDR,SCL ;force SCL low
sbi SDA_DDR,SDA ;force SDA low
rcall i2c_delay_T2 ;delay T/2
cbi SCL_DDR,SCL ;release SCL
rcall i2c_delay_T2 ;delay T/2
cbi SDA_DDR,SDA ;release SDA
rcall i2c_delay_T2 ;delay T/2
ret
.endfunc
;*************************************************************************
; Send one byte to I2C device
; return 0 = write successful, 1 = write failed
;
; extern unsigned char i2c_write( unsigned char data );
; data = r24, return = r25(=0):r24
;*************************************************************************
.global i2c_write
.func i2c_write
i2c_write:
sec ;set carry flag
rol r24 ;shift in carry and out bit one
rjmp i2c_write_first
i2c_write_bit:
lsl r24 ;if transmit register empty
i2c_write_first:
breq i2c_get_ack
sbi SCL_DDR,SCL ;force SCL low
brcc i2c_write_low
nop
cbi SDA_DDR,SDA ;release SDA
rjmp i2c_write_high
i2c_write_low:
sbi SDA_DDR,SDA ;force SDA low
rjmp i2c_write_high
i2c_write_high:
rcall i2c_delay_T2 ;delay T/2
cbi SCL_DDR,SCL ;release SCL
rcall i2c_delay_T2 ;delay T/2
rjmp i2c_write_bit
i2c_get_ack:
sbi SCL_DDR,SCL ;force SCL low
cbi SDA_DDR,SDA ;release SDA
rcall i2c_delay_T2 ;delay T/2
cbi SCL_DDR,SCL ;release SCL
i2c_ack_wait:
sbis SCL_IN,SCL ;wait SCL high (in case wait states are inserted)
rjmp i2c_ack_wait
clr r24 ;return 0
sbic SDA_IN,SDA ;if SDA high -> return 1
ldi r24,1
rcall i2c_delay_T2 ;delay T/2
clr r25
ret
.endfunc
;*************************************************************************
; read one byte from the I2C device, send ack or nak to device
; (ack=1, send ack, request more data from device
; ack=0, send nak, read is followed by a stop condition)
;
; extern unsigned char i2c_read(unsigned char ack);
; ack = r24, return = r25(=0):r24
; extern unsigned char i2c_readAck(void);
; extern unsigned char i2c_readNak(void);
; return = r25(=0):r24
;*************************************************************************
.global i2c_readAck
.global i2c_readNak
.global i2c_read
.func i2c_read
i2c_readNak:
clr r24
rjmp i2c_read
i2c_readAck:
ldi r24,0x01
i2c_read:
ldi r23,0x01 ;data = 0x01
i2c_read_bit:
sbi SCL_DDR,SCL ;force SCL low
cbi SDA_DDR,SDA ;release SDA (from previous ACK)
rcall i2c_delay_T2 ;delay T/2
cbi SCL_DDR,SCL ;release SCL
rcall i2c_delay_T2 ;delay T/2
i2c_read_stretch:
sbis SCL_IN, SCL ;loop until SCL is high (allow slave to stretch SCL)
rjmp i2c_read_stretch
clc ;clear carry flag
sbic SDA_IN,SDA ;if SDA is high
sec ; set carry flag
rol r23 ;store bit
brcc i2c_read_bit ;while receive register not full
i2c_put_ack:
sbi SCL_DDR,SCL ;force SCL low
cpi r24,1
breq i2c_put_ack_low ;if (ack=0)
cbi SDA_DDR,SDA ; release SDA
rjmp i2c_put_ack_high
i2c_put_ack_low: ;else
sbi SDA_DDR,SDA ; force SDA low
i2c_put_ack_high:
rcall i2c_delay_T2 ;delay T/2
cbi SCL_DDR,SCL ;release SCL
i2c_put_ack_wait:
sbis SCL_IN,SCL ;wait SCL high
rjmp i2c_put_ack_wait
rcall i2c_delay_T2 ;delay T/2
mov r24,r23
clr r25
ret
.endfunc