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- #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"
-
- #define I2C_READ 1
- #define I2C_WRITE 0
-
- #define I2C_ACK 1
- #define I2C_NACK 0
-
- // 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 mcu 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)
-
- static volatile uint8_t i2c_slave_buffer[SLAVE_BUFFER_SIZE] = {0};
-
- static volatile uint8_t slave_buffer_pos;
- static volatile bool slave_has_register_set = false;
-
- static uint8_t i2c_start(uint8_t address);
- static void i2c_stop(void);
- static uint8_t i2c_write(uint8_t data);
- static uint8_t i2c_read(uint8_t ack);
-
- // 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);
- }
-
- // i2c_device_addr: the i2c device to communicate with
- // addr: the memory address to read from the i2c device
- // dest: pointer to where read data is saved
- // len: the number of bytes to read
- //
- // NOTE: on error, the data in dest may have been modified
- bool i2c_master_read(uint8_t i2c_device_addr, uint8_t addr, uint8_t *dest, uint8_t len) {
- bool err;
- if (len == 0) return 0;
-
- err = i2c_start(i2c_device_addr + I2C_WRITE);
- if (err) return err;
- err = i2c_write(addr);
- if (err) return err;
-
- err = i2c_start(i2c_device_addr + I2C_READ);
- if (err) return err;
-
- for (uint8_t i = 0; i < len-1; ++i) {
- dest[i] = i2c_read(I2C_ACK);
- }
- dest[len-1] = i2c_read(I2C_NACK);
- i2c_stop();
-
- return 0;
- }
-
- // i2c_device_addr: the i2c device to communicate with
- // addr: the memory address at which to write in the i2c device
- // data: the data to be written
- // len: the number of bytes to write
- bool i2c_master_write(uint8_t i2c_device_addr, uint8_t addr, uint8_t *data, uint8_t len) {
- bool err;
-
- if (len == 0) return 0;
-
- err = i2c_start(i2c_device_addr + I2C_WRITE);
- if (err) return err;
- err = i2c_write(addr);
- if (err) return err;
-
- for (uint8_t i = 0; i < len; ++i) {
- err = i2c_write(data[i]);
- if (err) return err;
- }
- i2c_stop();
- return 0;
- }
-
- void i2c_slave_write(uint8_t addr, uint8_t data) {
- i2c_slave_buffer[addr] = data;
- }
-
- uint8_t i2c_slave_read(uint8_t addr) {
- return i2c_slave_buffer[addr];
- }
-
- // 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_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_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_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_read(uint8_t ack) {
- TWCR = (1<<TWINT) | (1<<TWEN) | (ack<<TWEA);
-
- i2c_delay();
- return TWDR;
- }
-
- 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);
- }
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