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+/*************************************************************************
+* Title: I2C master library using hardware TWI interface
+* Author: Peter Fleury <pfleury@gmx.ch> 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 16000000UL
+#endif
+
+/* I2C clock in Hz */
+#define SCL_CLOCK 400000L
+
+
+/*************************************************************************
+ Initialization of the I2C bus interface. Need to be called only once
+*************************************************************************/
+void i2c_init(void)
+{
+ /* initialize TWI clock
+ * minimal values in Bit Rate Register (TWBR) and minimal Prescaler
+ * bits in the TWI Status Register should give us maximal possible
+ * I2C bus speed - about 444 kHz
+ *
+ * for more details, see 20.5.2 in ATmega16/32 secification
+ */
+
+ TWSR = 0; /* no prescaler */
+ TWBR = 10; /* must be >= 10 for stable operation */
+
+}/* i2c_init */
+
+
+/*************************************************************************
+ Issues a start condition and sends address and transfer direction.
+ return 0 = device accessible, 1= failed to access device
+*************************************************************************/
+unsigned char i2c_start(unsigned char address)
+{
+ uint8_t twst;
+
+ // send START condition
+ TWCR = (1<<TWINT) | (1<<TWSTA) | (1<<TWEN);
+
+ // wait until transmission completed
+ 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 1;
+
+ // send device address
+ TWDR = address;
+ TWCR = (1<<TWINT) | (1<<TWEN);
+
+ // wail until transmission completed and ACK/NACK has been received
+ 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 1;
+
+ return 0;
+
+}/* 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
+*************************************************************************/
+void i2c_start_wait(unsigned char address)
+{
+ uint8_t twst;
+
+
+ while ( 1 )
+ {
+ // send START condition
+ TWCR = (1<<TWINT) | (1<<TWSTA) | (1<<TWEN);
+
+ // wait until transmission completed
+ 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
+ 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
+ while(TWCR & (1<<TWSTO));
+
+ continue;
+ }
+ //if( twst != TW_MT_SLA_ACK) return 1;
+ break;
+ }
+
+}/* i2c_start_wait */
+
+
+/*************************************************************************
+ Issues a repeated start condition and sends address and transfer direction
+
+ Input: address and transfer direction of I2C device
+
+ Return: 0 device accessible
+ 1 failed to access device
+*************************************************************************/
+unsigned char i2c_rep_start(unsigned char address)
+{
+ return i2c_start( address );
+
+}/* i2c_rep_start */
+
+
+/*************************************************************************
+ Terminates the data transfer and releases the I2C bus
+*************************************************************************/
+void i2c_stop(void)
+{
+ /* send stop condition */
+ TWCR = (1<<TWINT) | (1<<TWEN) | (1<<TWSTO);
+
+ // wait until stop condition is executed and bus released
+ while(TWCR & (1<<TWSTO));
+
+}/* i2c_stop */
+
+
+/*************************************************************************
+ Send one byte to I2C device
+
+ Input: byte to be transfered
+ Return: 0 write successful
+ 1 write failed
+*************************************************************************/
+unsigned char 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
+ while(!(TWCR & (1<<TWINT)));
+
+ // check value of TWI Status Register. Mask prescaler bits
+ twst = TW_STATUS & 0xF8;
+ if( twst != TW_MT_DATA_ACK) return 1;
+ return 0;
+
+}/* i2c_write */
+
+
+/*************************************************************************
+ Read one byte from the I2C device, request more data from device
+
+ Return: byte read from I2C device
+*************************************************************************/
+unsigned char i2c_readAck(void)
+{
+ TWCR = (1<<TWINT) | (1<<TWEN) | (1<<TWEA);
+ while(!(TWCR & (1<<TWINT)));
+
+ return TWDR;
+
+}/* i2c_readAck */
+
+
+/*************************************************************************
+ Read one byte from the I2C device, read is followed by a stop condition
+
+ Return: byte read from I2C device
+*************************************************************************/
+unsigned char i2c_readNak(void)
+{
+ TWCR = (1<<TWINT) | (1<<TWEN);
+ while(!(TWCR & (1<<TWINT)));
+
+ return TWDR;
+
+}/* i2c_readNak */