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/*
* Copyright 2021 Daniel Friesel
*
* SPDX-License-Identifier: BSD-2-Clause
*/
#include "driver/i2c.h"
#include "arch.h"
#include <avr/io.h>
#include <avr/interrupt.h>
#ifndef F_I2C
#define F_I2C 100000UL
#endif
// TODO timeouts (e.g. stuck bus or missing pull-ups)
inline void await_twint(unsigned char twcr_values)
{
TWCR = twcr_values | _BV(TWINT) | _BV(TWIE);
while (!(TWCR & _BV(TWINT))) {
arch.idle();
}
}
/*
* Send an I2C (re)start condition and the device address in read mode. Returns
* after it has been transmitted successfully.
*/
static signed char i2c_start_read(unsigned char addr)
{
await_twint(_BV(TWSTA) | _BV(TWEN));
if (!(TWSR & 0x18)) // 0x08 == START ok, 0x10 == RESTART ok
return -1;
// Note: The R byte ("... | 1") causes the TWI module to switch to
// Master Receive mode
TWDR = (addr << 1) | 1;
await_twint(_BV(TWEN));
if (TWSR != 0x40) // 0x40 == SLA+R transmitted, ACK receveid
return -2;
return 0;
}
/*
* Send an I2C (re)start condition and the device address in write mode.
* Returns after it has been transmitted successfully.
*/
static signed char i2c_start_write(unsigned char addr)
{
await_twint(_BV(TWSTA) | _BV(TWEN));
if (!(TWSR & 0x18)) // 0x08 == START ok, 0x10 == RESTART ok
return -1;
TWDR = (addr<< 1) | 0;
await_twint(_BV(TWEN));
if (TWSR != 0x18) // 0x18 == SLA+W transmitted, ACK received
return -2;
return 0;
}
/*
* Send an I2C stop condition.
*/
static signed char i2c_stop()
{
TWCR = _BV(TWINT) | _BV(TWSTO) | _BV(TWEN);
return 0;
}
/*
* Sends len bytes to the device. Note that this method does NOT
* send I2C start or stop conditions.
*/
static signed char i2c_send(uint8_t len, uint8_t *data)
{
uint8_t pos = 0;
for (pos = 0; pos < len; pos++) {
TWDR = data[pos];
await_twint(_BV(TWEN));
if (TWSR != 0x28) // 0x28 == byte transmitted, ACK received
return pos;
}
return pos;
}
/*
* Receives len bytes from the device into data. Note that this method does
* NOT send I2C start or stop conditions.
*/
static signed char i2c_receive(uint8_t len, uint8_t *data)
{
uint8_t pos = 0;
for (pos = 0; pos < len; pos++) {
await_twint(_BV(TWEN) | ( _BV(TWEA) * (pos < len-1) ) );
data[pos] = TWDR;
/*
* No error handling here -- We send the acks, the device only
* supplies raw data, so there's no way of knowing whether it's still
* talking to us or we're just reading garbage.
*/
}
return pos;
}
signed char I2C::setup()
{
TWSR = 0;
TWBR = ((F_CPU / F_I2C) - 16) / 2;
return 0;
}
void I2C::scan(unsigned int *results)
{
for (unsigned char address = 0; address < 128; address++) {
if (i2c_start_read(address) == 0) {
results[address / (8 * sizeof(unsigned int))] |= 1 << (address % (8 * sizeof(unsigned int)));
i2c_stop();
}
}
i2c_stop();
}
signed char I2C::xmit(unsigned char address,
unsigned char tx_len, unsigned char *tx_buf,
unsigned char rx_len, unsigned char *rx_buf)
{
if (tx_len) {
if (i2c_start_write(address) < 0) {
return -1;
}
if (i2c_send(tx_len, tx_buf) < 0) {
return -1;
}
}
if (rx_len) {
if (i2c_start_read(address) < 0) {
return -1;
}
if (i2c_receive(rx_len, rx_buf) < 0) {
return -1;
}
}
i2c_stop();
return 0;
}
I2C i2c;
ISR(TWI_vect)
{
}
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