162 lines
3.2 KiB
C
162 lines
3.2 KiB
C
/* software bit banging implementation
|
|
* based on https://en.wikipedia.org/wiki/I2c example code
|
|
*/
|
|
#include "I2C.h"
|
|
|
|
// Hardware-specific support functions that MUST be customized:
|
|
#define I2CSPEED 100
|
|
void I2C_delay()
|
|
{
|
|
volatile int v = 0;
|
|
int i;
|
|
for (i=0; i < I2CSPEED/2; i++) {
|
|
v;
|
|
}
|
|
}
|
|
|
|
/* Set SCL as input and return current level of line, 0 or 1 */
|
|
bool read_SCL(void)
|
|
{
|
|
PORTB |= SCL; /* set as input */
|
|
WPUB |= SCL; /* enable pull-up */
|
|
return (PORTB&SCL);
|
|
}
|
|
|
|
/* Set SDA as input and return current level of line, 0 or 1 */
|
|
bool read_SDA(void)
|
|
{
|
|
PORTB |= SDA; /* set as input */
|
|
WPUB |= SDA; /* enable pull-up */
|
|
return (PORTB&SDA);
|
|
}
|
|
|
|
/* Actively drive SCL signal low */
|
|
void clear_SCL(void)
|
|
{
|
|
PORTB &= ~SCL; /* set as output */
|
|
PORTB &= ~SDA; /* set low */
|
|
}
|
|
|
|
/* Actively drive SDA signal low */
|
|
void clear_SDA(void)
|
|
{
|
|
PORTB &= ~SCL; /* set as output */
|
|
PORTB &= ~SDA; /* set low */
|
|
}
|
|
|
|
void arbitration_lost(void)
|
|
{
|
|
/* do nothing, since we are the only master */
|
|
}
|
|
|
|
bool started = false; // global data
|
|
void i2c_start_cond(void) {
|
|
if (started) { // if started, do a restart cond
|
|
// set SDA to 1
|
|
read_SDA();
|
|
I2C_delay();
|
|
while (read_SCL() == 0) { // Clock stretching
|
|
// You should add timeout to this loop
|
|
}
|
|
// Repeated start setup time, minimum 4.7us
|
|
I2C_delay();
|
|
}
|
|
if (read_SDA() == 0) {
|
|
arbitration_lost();
|
|
}
|
|
// SCL is high, set SDA from 1 to 0.
|
|
clear_SDA();
|
|
I2C_delay();
|
|
clear_SCL();
|
|
started = true;
|
|
}
|
|
|
|
void i2c_stop_cond(void){
|
|
// set SDA to 0
|
|
clear_SDA();
|
|
I2C_delay();
|
|
// Clock stretching
|
|
while (read_SCL() == 0) {
|
|
// add timeout to this loop.
|
|
}
|
|
// Stop bit setup time, minimum 4us
|
|
I2C_delay();
|
|
// SCL is high, set SDA from 0 to 1
|
|
if (read_SDA() == 0) {
|
|
arbitration_lost();
|
|
}
|
|
I2C_delay();
|
|
started = false;
|
|
}
|
|
|
|
// Write a bit to I2C bus
|
|
void i2c_write_bit(bool bit) {
|
|
if (bit) {
|
|
read_SDA();
|
|
} else {
|
|
clear_SDA();
|
|
}
|
|
I2C_delay();
|
|
while (read_SCL() == 0) { // Clock stretching
|
|
// You should add timeout to this loop
|
|
}
|
|
// SCL is high, now data is valid
|
|
// If SDA is high, check that nobody else is driving SDA
|
|
if (bit && read_SDA() == 0) {
|
|
arbitration_lost();
|
|
}
|
|
I2C_delay();
|
|
clear_SCL();
|
|
}
|
|
|
|
// Read a bit from I2C bus
|
|
bool i2c_read_bit(void) {
|
|
bool bit;
|
|
// Let the slave drive data
|
|
read_SDA();
|
|
I2C_delay();
|
|
while (read_SCL() == 0) { // Clock stretching
|
|
// You should add timeout to this loop
|
|
}
|
|
// SCL is high, now data is valid
|
|
bit = read_SDA();
|
|
I2C_delay();
|
|
clear_SCL();
|
|
return bit;
|
|
}
|
|
|
|
// Write a byte to I2C bus. Return 0 if ack by the slave.
|
|
bool i2c_write_byte(bool send_start,
|
|
bool send_stop,
|
|
unsigned char byte) {
|
|
unsigned bit;
|
|
bool nack;
|
|
if (send_start) {
|
|
i2c_start_cond();
|
|
}
|
|
for (bit = 0; bit < 8; bit++) {
|
|
i2c_write_bit((byte & 0x80) != 0);
|
|
byte <<= 1;
|
|
}
|
|
nack = i2c_read_bit();
|
|
if (send_stop) {
|
|
i2c_stop_cond();
|
|
}
|
|
return nack;
|
|
}
|
|
|
|
// Read a byte from I2C bus
|
|
unsigned char i2c_read_byte(bool nack, bool send_stop) {
|
|
unsigned char byte = 0;
|
|
unsigned bit;
|
|
for (bit = 0; bit < 8; bit++) {
|
|
byte = (byte << 1) | i2c_read_bit();
|
|
}
|
|
i2c_write_bit(nack);
|
|
if (send_stop) {
|
|
i2c_stop_cond();
|
|
}
|
|
return byte;
|
|
}
|
|
|