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/* Library made by: g4lvanix
* Github repository: https://github.com/g4lvanix/I2C-slave-lib
*/
#include <avr/io.h>
#include <util/twi.h>
#include <avr/interrupt.h>
#include <stdbool.h>
#include "i2c_slave.h"
volatile uint8_t i2c_slave_reg[I2C_SLAVE_REG_COUNT];
static volatile uint8_t buffer_address;
static volatile bool slave_has_register_set = false;
void i2c_slave_init(uint8_t address){
// load address into TWI address register
TWAR = address;
// set the TWCR to enable address matching and enable TWI, clear TWINT, enable TWI interrupt
TWCR = (1 << TWIE) | (1 << TWEA) | (1 << TWINT) | (1 << TWEN);
}
void i2c_slave_stop(void){
// clear acknowledge and enable bits
TWCR &= ~((1 << TWEA) | (1 << TWEN));
}
ISR(TWI_vect){
uint8_t ack = 1;
switch(TW_STATUS){
case TW_SR_SLA_ACK:
// The device is now a slave receiver
slave_has_register_set = false;
break;
case TW_SR_DATA_ACK:
// This device is a slave receiver and has received data
// First byte is the location then the bytes will be writen in buffer with auto-incriment
if(!slave_has_register_set){
buffer_address = TWDR;
if (buffer_address >= I2C_SLAVE_REG_COUNT) { // address out of bounds dont ack
ack = 0;
buffer_address = 0;
}
slave_has_register_set = true; // address has been receaved now fill in buffer
} else {
i2c_slave_reg[buffer_address] = TWDR;
buffer_address++;
}
break;
case TW_ST_SLA_ACK:
case TW_ST_DATA_ACK:
// This device is a slave transmitter and master has requested data
TWDR = i2c_slave_reg[buffer_address];
buffer_address++;
break;
case TW_BUS_ERROR:
// We got an error, reset i2c
TWCR = 0;
default:
break;
}
// Reset i2c state machine to be ready for next interrupt
TWCR |= (1 << TWIE) | (1 << TWINT) | (ack << TWEA) | (1 << TWEN);
}
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