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twimaster.c
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/*************************************************************************
* Title: I2C master library using hardware TWI interface
* Author: Peter Fleury <[email protected]> http://jump.to/fleury
* File: $Id: twimaster.c,v 1.3 2005/07/02 11:14:21 Peter Exp $
* Software: AVR-GCC 3.4.3 / avr-libc 1.2.3
* Target: any AVR device with hardware TWI
* Usage: API compatible with I2C Software Library i2cmaster.h
**************************************************************************/
#include <inttypes.h>
#include <compat/twi.h>
#include <i2cmaster.h>
/* define CPU frequency in Mhz here if not defined in Makefile */
#ifndef F_CPU
#define F_CPU 12000000UL
#endif
/* I2C clock in Hz */
#define SCL_CLOCK 100000L
/* I2C timeout */
#define I2C_TIMEOUT 2000UL
/* wait with timeout */
#define I2C_wait_while(condition) {\
uint16_t timeout = I2C_TIMEOUT; \
while (condition) { \
if (timeout-- == 0) { \
TWCR = 0; \
return I2C_ERROR_TIMEOUT; \
} \
} \
}
/*************************************************************************
Initialization of the I2C bus interface. Need to be called only once
*************************************************************************/
void i2c_init(void)
{
/* initialize TWI clock: 100 kHz clock, TWPS = 0 => prescaler = 1 */
TWSR = 0; /* no prescaler */
TWBR = ((F_CPU/SCL_CLOCK)-16)/2; /* must be > 10 for stable operation */
}/* i2c_init */
/*************************************************************************
Issues a start condition and sends address and transfer direction.
return I2C_SUCCESS = device accessible, I2C_ERROR_*= failed to access device
*************************************************************************/
uint16_t i2c_start(unsigned char address)
{
uint8_t twst;
// send START condition
TWCR = (1<<TWINT) | (1<<TWSTA) | (1<<TWEN);
// wait until transmission completed
I2C_wait_while(!(TWCR & (1<<TWINT)));
// check value of TWI Status Register. Mask prescaler bits.
twst = TW_STATUS & 0xF8;
if ( (twst != TW_START) && (twst != TW_REP_START)) return I2C_ERROR_START;
// send device address
TWDR = address;
TWCR = (1<<TWINT) | (1<<TWEN);
// wail until transmission completed and ACK/NACK has been received
I2C_wait_while(!(TWCR & (1<<TWINT)));
// check value of TWI Status Register. Mask prescaler bits.
twst = TW_STATUS & 0xF8;
if ( (twst != TW_MT_SLA_ACK) && (twst != TW_MR_SLA_ACK) ) return I2C_ERROR_WRITE;
return I2C_SUCCESS;
}/* i2c_start */
/*************************************************************************
Issues a start condition and sends address and transfer direction.
If device is busy, use ack polling to wait until device is ready
Input: address and transfer direction of I2C device
*************************************************************************/
uint16_t i2c_start_wait(unsigned char address)
{
uint8_t twst;
uint8_t timeout = 10;
while ( timeout-- > 0 )
{
// send START condition
TWCR = (1<<TWINT) | (1<<TWSTA) | (1<<TWEN);
// wait until transmission completed
I2C_wait_while(!(TWCR & (1<<TWINT)));
// check value of TWI Status Register. Mask prescaler bits.
twst = TW_STATUS & 0xF8;
if ( (twst != TW_START) && (twst != TW_REP_START)) continue;
// send device address
TWDR = address;
TWCR = (1<<TWINT) | (1<<TWEN);
// wail until transmission completed
I2C_wait_while(!(TWCR & (1<<TWINT)));
// check value of TWI Status Register. Mask prescaler bits.
twst = TW_STATUS & 0xF8;
if ( (twst == TW_MT_SLA_NACK )||(twst ==TW_MR_DATA_NACK) )
{
/* device busy, send stop condition to terminate write operation */
TWCR = (1<<TWINT) | (1<<TWEN) | (1<<TWSTO);
// wait until stop condition is executed and bus released
I2C_wait_while(TWCR & (1<<TWSTO));
continue;
}
//if( twst != TW_MT_SLA_ACK) return 1;
break;
}
if (timeout)
return I2C_SUCCESS;
else
return I2C_ERROR_TIMEOUT;
}/* i2c_start_wait */
/*************************************************************************
Issues a repeated start condition and sends address and transfer direction
Input: address and transfer direction of I2C device
Return: I2C_SUCCESS device accessible
I2C_ERROR_* failed to access device
*************************************************************************/
uint16_t i2c_rep_start(unsigned char address)
{
return i2c_start( address );
}/* i2c_rep_start */
/*************************************************************************
Terminates the data transfer and releases the I2C bus
*************************************************************************/
uint16_t i2c_stop(void)
{
/* send stop condition */
TWCR = (1<<TWINT) | (1<<TWEN) | (1<<TWSTO);
// wait until stop condition is executed and bus released
I2C_wait_while(TWCR & (1<<TWSTO));
return I2C_SUCCESS;
}/* i2c_stop */
/*************************************************************************
Send one byte to I2C device
Input: byte to be transfered
Return: I2C_SUCCESS write successful
I2C_ERROR_* write failed
*************************************************************************/
uint16_t i2c_write( unsigned char data )
{
uint8_t twst;
// send data to the previously addressed device
TWDR = data;
TWCR = (1<<TWINT) | (1<<TWEN);
// wait until transmission completed
I2C_wait_while(!(TWCR & (1<<TWINT)));
// check value of TWI Status Register. Mask prescaler bits
twst = TW_STATUS & 0xF8;
if( twst != TW_MT_DATA_ACK) return I2C_ERROR_WRITE;
return I2C_SUCCESS;
}/* i2c_write */
/*************************************************************************
Read one byte from the I2C device, request more data from device
Return: byte read from I2C device
*************************************************************************/
uint16_t i2c_readAck(void)
{
TWCR = (1<<TWINT) | (1<<TWEN) | (1<<TWEA);
I2C_wait_while(!(TWCR & (1<<TWINT)));
return (uint8_t) TWDR;
}/* i2c_readAck */
/*************************************************************************
Read one byte from the I2C device, read is followed by a stop condition
Return: byte read from I2C device
*************************************************************************/
uint16_t i2c_readNak(void)
{
TWCR = (1<<TWINT) | (1<<TWEN);
I2C_wait_while(!(TWCR & (1<<TWINT)));
return (uint8_t) TWDR;
}/* i2c_readNak */