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1. Slow down I2C to 100khz During Reset

Browse Source 
I am stealing this delay coding from @jeremyherbert #2493 pr.

2. Change Bus Reset to handle interrupted READ sequences.

The current code does not handle interrupted READ cycles.

 If a SLAVE device was in a read operation when the bus was interrupted, the SLAVE device is controlling SDA.

The only bit during the 9 clock cycles of a byte READ the MASTER(ESP32) is guaranteed control over, is during the ACK bit period.

If the SLAVE is sending a stream of ZERO bytes, it will only release SDA during the ACK bit period. The master(ESP32) cannot generate a STOP unless SDA is HIGH.

So, this reset code synchronizes the bit stream with, Either, the ACK bit, Or a 1 bit.

3. fix typo

correct `sda_id` to `sda_io` in `i2c_master_clear_bus()` @ryan-ma found it.  This typo was generated when I manually edited this patch on GitHub, I should have done a Copy/Paste operation!
This commit is contained in:
chuck todd 2018-09-30 14:47:05 -06:00 committed by morris
parent 34c1d25c7f
commit e55f9c1e98
1 changed files with 14 additions and 12 deletions
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22
components/driver/i2c.c
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@ -537,27 +537,29 @@ static esp_err_t i2c_master_clear_bus(i2c_port_t i2c_num)
int sda_io = GPIO.func_in_sel_cfg[sda_in_sig].func_sel;
I2C_CHECK((GPIO_IS_VALID_OUTPUT_GPIO(scl_io)), I2C_SCL_IO_ERR_STR, ESP_ERR_INVALID_ARG);
I2C_CHECK((GPIO_IS_VALID_GPIO(sda_io)), I2C_SDA_IO_ERR_STR, ESP_ERR_INVALID_ARG);
// We do not check whether the SDA line is low
// because after some serious interference, the bus may keep high all the time and the i2c bus is out of service.
gpio_set_direction(scl_io, GPIO_MODE_OUTPUT_OD);
gpio_set_direction(sda_io, GPIO_MODE_OUTPUT_OD);
// If a SLAVE device was in a read operation when the bus was interrupted, the SLAVE device is controlling SDA.
// The only bit during the 9 clock cycles of a READ byte the MASTER(ESP32) is guaranteed control over is during the ACK bit
// period. If the slave is sending a stream of ZERO bytes, it will only release SDA during the ACK bit period.
// So, this reset code needs to synchronize the bit stream with, Either, the ACK bit, Or a 1 bit to correctly generate
// a STOP condition.
int scl_half_period = 5; // use standard 100kHz data rate
gpio_set_level(scl_io, 0);
gpio_set_level(sda_io, 1);
ets_delay_us(scl_half_period);
int i=0;
while( !gpio_get_level(sda_io) && (i<9)){ // cycle SCL until SDA is HIGH
gpio_set_level(scl_io, 1);
ets_delay_us(scl_half_period);
for (int i = 0; i < 9; i++) {
gpio_set_level(scl_io, 0);
ets_delay_us(scl_half_period);
i++;
}
gpio_set_level(sda_io,0); // setup for STOP
gpio_set_level(scl_io,1);
ets_delay_us(scl_half_period);
}
gpio_set_level(sda_io, 0); // setup stop condition (this is an implicit start condition)
ets_delay_us(scl_half_period);
gpio_set_level(sda_io, 1); // generate stop condition
ets_delay_us(scl_half_period);
gpio_set_level(sda_io, 1); // STOP, SDA low -> high while SCL is HIGH
i2c_set_pin(i2c_num, sda_io, scl_io, 1, 1, I2C_MODE_MASTER);
return ESP_OK;
}