#include <util/twi.h> #include <avr/io.h> #include <stdlib.h> #include <avr/interrupt.h> #include <util/twi.h> #include <stdbool.h> #include "i2c.h" // Limits the amount of we wait for any one i2c transaction. // Since were running SCL line 100kHz (=> 10μs/bit), and each transactions is // 9 bits, a single transaction will take around 90μs to complete. // // (F_CPU/SCL_CLOCK) => # of μC cycles to transfer a bit // poll loop takes at least 8 clock cycles to execute #define I2C_LOOP_TIMEOUT (9+1)*(F_CPU/SCL_CLOCK)/8 #define BUFFER_POS_INC() (slave_buffer_pos = (slave_buffer_pos+1)%SLAVE_BUFFER_SIZE) volatile uint8_t i2c_slave_buffer[SLAVE_BUFFER_SIZE]; static volatile uint8_t slave_buffer_pos; static volatile bool slave_has_register_set = false; // Wait for an i2c operation to finish inline static void i2c_delay(void) { uint16_t lim = 0; while(!(TWCR & (1<<TWINT)) && lim < I2C_LOOP_TIMEOUT) lim++; // easier way, but will wait slightly longer // _delay_us(100); } // Setup twi to run at 100kHz void i2c_master_init(void) { // no prescaler TWSR = 0; // Set TWI clock frequency to SCL_CLOCK. Need TWBR>10. // Check datasheets for more info. TWBR = ((F_CPU/SCL_CLOCK)-16)/2; } // Start a transaction with the given i2c slave address. The direction of the // transfer is set with I2C_READ and I2C_WRITE. // returns: 0 => success // 1 => error uint8_t i2c_master_start(uint8_t address) { TWCR = (1<<TWINT) | (1<<TWEN) | (1<<TWSTA); i2c_delay(); // check that we started successfully if ( (TW_STATUS != TW_START) && (TW_STATUS != TW_REP_START)) return 1; TWDR = address; TWCR = (1<<TWINT) | (1<<TWEN); i2c_delay(); if ( (TW_STATUS != TW_MT_SLA_ACK) && (TW_STATUS != TW_MR_SLA_ACK) ) return 1; // slave did not acknowledge else return 0; // success } // Finish the i2c transaction. void i2c_master_stop(void) { TWCR = (1<<TWINT) | (1<<TWEN) | (1<<TWSTO); uint16_t lim = 0; while(!(TWCR & (1<<TWSTO)) && lim < I2C_LOOP_TIMEOUT) lim++; } // Write one byte to the i2c slave. // returns 0 => slave ACK // 1 => slave NACK uint8_t i2c_master_write(uint8_t data) { TWDR = data; TWCR = (1<<TWINT) | (1<<TWEN); i2c_delay(); // check if the slave acknowledged us return (TW_STATUS == TW_MT_DATA_ACK) ? 0 : 1; } // Read one byte from the i2c slave. If ack=1 the slave is acknowledged, // if ack=0 the acknowledge bit is not set. // returns: byte read from i2c device uint8_t i2c_master_read(int ack) { TWCR = (1<<TWINT) | (1<<TWEN) | (ack<<TWEA); i2c_delay(); return TWDR; } void i2c_reset_state(void) { TWCR = 0; } void i2c_slave_init(uint8_t address) { TWAR = address << 0; // slave i2c address // TWEN - twi enable // TWEA - enable address acknowledgement // TWINT - twi interrupt flag // TWIE - enable the twi interrupt TWCR = (1<<TWIE) | (1<<TWEA) | (1<<TWINT) | (1<<TWEN); } ISR(TWI_vect); ISR(TWI_vect) { uint8_t ack = 1; switch(TW_STATUS) { case TW_SR_SLA_ACK: // this device has been addressed as a slave receiver slave_has_register_set = false; break; case TW_SR_DATA_ACK: // this device has received data as a slave receiver // The first byte that we receive in this transaction sets the location // of the read/write location of the slaves memory that it exposes over // i2c. After that, bytes will be written at slave_buffer_pos, incrementing // slave_buffer_pos after each write. if(!slave_has_register_set) { slave_buffer_pos = TWDR; // don't acknowledge the master if this memory loctaion is out of bounds if ( slave_buffer_pos >= SLAVE_BUFFER_SIZE ) { ack = 0; slave_buffer_pos = 0; } slave_has_register_set = true; } else { i2c_slave_buffer[slave_buffer_pos] = TWDR; BUFFER_POS_INC(); } break; case TW_ST_SLA_ACK: case TW_ST_DATA_ACK: // master has addressed this device as a slave transmitter and is // requesting data. TWDR = i2c_slave_buffer[slave_buffer_pos]; BUFFER_POS_INC(); break; case TW_BUS_ERROR: // something went wrong, reset twi state TWCR = 0; default: break; } // Reset everything, so we are ready for the next TWI interrupt TWCR |= (1<<TWIE) | (1<<TWINT) | (ack<<TWEA) | (1<<TWEN); }