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i2c_bb.c
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i2c_bb.c
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/*
Copyright 2019 Benjamin Vedder [email protected]
This file is part of the VESC firmware.
The VESC firmware is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
The VESC firmware is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
#include "i2c_bb.h"
#include "timer.h"
// This is based on https://en.wikipedia.org/wiki/I%C2%B2C
// Macros
#define SDA_LOW() palClearPad(s->sda_gpio, s->sda_pin)
#define SDA_HIGH() palSetPad(s->sda_gpio, s->sda_pin)
#define SCL_LOW() palClearPad(s->scl_gpio, s->scl_pin)
#define SCL_HIGH() palSetPad(s->scl_gpio, s->scl_pin)
#define READ_SDA() palReadPad(s->sda_gpio, s->sda_pin)
#define READ_SCL() palReadPad(s->scl_gpio, s->scl_pin)
// Private functions
static void i2c_start_cond(i2c_bb_state *s);
static void i2c_stop_cond(i2c_bb_state *s);
static void i2c_write_bit(i2c_bb_state *s, bool bit);
static bool i2c_read_bit(i2c_bb_state *s);
static bool i2c_write_byte(i2c_bb_state *s, bool send_start, bool send_stop, unsigned char byte);
static unsigned char i2c_read_byte(i2c_bb_state *s, bool nack, bool send_stop);
static bool clock_stretch_timeout(i2c_bb_state *s);
static void i2c_delay(void);
void i2c_bb_init(i2c_bb_state *s) {
chMtxObjectInit(&s->mutex);
palSetPadMode(s->sda_gpio, s->sda_pin, PAL_MODE_OUTPUT_OPENDRAIN);
palSetPadMode(s->scl_gpio, s->scl_pin, PAL_MODE_OUTPUT_OPENDRAIN);
s->has_started = false;
s->has_error = false;
}
void i2c_bb_restore_bus(i2c_bb_state *s) {
chMtxLock(&s->mutex);
SCL_HIGH();
SDA_HIGH();
chThdSleep(1);
for(int i = 0;i < 16;i++) {
SCL_LOW();
chThdSleep(1);
SCL_HIGH();
chThdSleep(1);
}
s->has_started = false;
i2c_start_cond(s);
i2c_stop_cond(s);
s->has_error = false;
chMtxUnlock(&s->mutex);
}
bool i2c_bb_tx_rx(i2c_bb_state *s, uint16_t addr, uint8_t *txbuf, size_t txbytes, uint8_t *rxbuf, size_t rxbytes) {
chMtxLock(&s->mutex);
i2c_write_byte(s, true, false, addr << 1);
for (unsigned int i = 0;i < txbytes;i++) {
i2c_write_byte(s, false, false, txbuf[i]);
}
if (rxbytes > 0) {
i2c_write_byte(s, true, false, addr << 1 | 1);
for (unsigned int i = 0;i < rxbytes;i++) {
rxbuf[i] = i2c_read_byte(s, i == (rxbytes - 1), false);
}
}
i2c_stop_cond(s);
chMtxUnlock(&s->mutex);
return !s->has_error;
}
static void i2c_start_cond(i2c_bb_state *s) {
if (s->has_started) {
// if started, do a restart condition
SDA_HIGH();
i2c_delay();
SCL_HIGH();
if (!clock_stretch_timeout(s)) {
return;
}
// Repeated start setup time, minimum 4.7us
i2c_delay();
}
if (READ_SDA() == 0) {
// arbitration_lost();
s->has_error = true;
}
// SCL is high, set SDA from 1 to 0.
SDA_LOW();
i2c_delay();
SCL_LOW();
s->has_started = true;
}
static void i2c_stop_cond(i2c_bb_state *s) {
SDA_LOW();
i2c_delay();
SCL_HIGH();
if (!clock_stretch_timeout(s)) {
return;
}
// Stop bit setup time, minimum 4us
i2c_delay();
// SCL is high, set SDA from 0 to 1
SDA_HIGH();
i2c_delay();
if (READ_SDA() == 0) {
// arbitration_lost();
s->has_error = true;
}
s->has_started = false;
}
static void i2c_write_bit(i2c_bb_state *s, bool bit) {
if (bit) {
SDA_HIGH();
} else {
SDA_LOW();
}
// SDA change propagation delay
i2c_delay();
// Set SCL high to indicate a new valid SDA value is available
SCL_HIGH();
// Wait for SDA value to be read by slave, minimum of 4us for standard mode
i2c_delay();
if (!clock_stretch_timeout(s)) {
return;
}
// 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();
s->has_error = true;
}
// Clear the SCL to low in preparation for next change
SCL_LOW();
}
static bool i2c_read_bit(i2c_bb_state *s) {
bool bit;
// Let the slave drive data
SDA_HIGH();
// Wait for SDA value to be written by slave, minimum of 4us for standard mode
i2c_delay();
// Set SCL high to indicate a new valid SDA value is available
SCL_HIGH();
if (!clock_stretch_timeout(s)) {
return false;
}
// Wait for SDA value to be written by slave, minimum of 4us for standard mode
i2c_delay();
// SCL is high, read out bit
bit = READ_SDA();
// Set SCL low in preparation for next operation
SCL_LOW();
return bit;
}
static bool i2c_write_byte(i2c_bb_state *s, bool send_start, bool send_stop, unsigned char byte) {
unsigned bit;
bool nack;
if (send_start) {
i2c_start_cond(s);
}
for (bit = 0;bit < 8;bit++) {
i2c_write_bit(s, (byte & 0x80) != 0);
byte <<= 1;
}
nack = i2c_read_bit(s);
if (send_stop) {
i2c_stop_cond(s);
}
return nack;
}
static unsigned char i2c_read_byte(i2c_bb_state *s, bool nack, bool send_stop) {
unsigned char byte = 0;
unsigned char bit;
for (bit = 0;bit < 8;bit++) {
byte = (byte << 1) | i2c_read_bit(s);
}
i2c_write_bit(s, nack);
if (send_stop) {
i2c_stop_cond(s);
}
return byte;
}
static bool clock_stretch_timeout(i2c_bb_state *s) {
uint32_t time_start = timer_time_now();
while(READ_SCL() == 0) {
if (timer_seconds_elapsed_since(time_start) > 0.01) {
s->has_error = true;
return false;
}
}
return true;
}
static void i2c_delay(void) {
timer_sleep(1e-6);
}