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Merge pull request #10127 from gschorcht/esp8266_i2c_fix

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cpu/esp8266: improvements of I2C implementation
This commit is contained in:
Kevin "Bear Puncher" Weiss 2018-10-10 17:13:34 +02:00 committed by GitHub
commit 9a75ee0d47
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GPG Key ID: 4AEE18F83AFDEB23
2 changed files with 150 additions and 67 deletions
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3
cpu/esp8266/periph/gpio.c
View File

@ -150,7 +150,8 @@ int gpio_init(gpio_t pin, gpio_mode_t mode)
case GPIO_IN_PU: iomux_conf |= IOMUX_PIN_PULLUP; case GPIO_IN_PU: iomux_conf |= IOMUX_PIN_PULLUP;
iomux_conf |= IOMUX_PIN_PULLUP_SLEEP; iomux_conf |= IOMUX_PIN_PULLUP_SLEEP;
case GPIO_IN: GPIO.ENABLE_OUT_CLEAR = BIT(pin); case GPIO_IN: GPIO.CONF[pin] |= GPIO_CONF_OPEN_DRAIN;
GPIO.ENABLE_OUT_CLEAR = BIT(pin);
break; break;
case GPIO_IN_PD: LOG_ERROR("GPIO mode GPIO_IN_PD is not supported.\n"); case GPIO_IN_PD: LOG_ERROR("GPIO mode GPIO_IN_PD is not supported.\n");

214
cpu/esp8266/periph/i2c.c
View File

@ -98,14 +98,17 @@ static _i2c_bus_t _i2c_bus[] =
#endif #endif
}; };
/* to ensure that I2C is always optimized with -O2 to use the defined delays */
#pragma GCC optimize ("O2")
static const uint32_t _i2c_delays[][2] = static const uint32_t _i2c_delays[][2] =
{ {
/* values specify one half-period and are only valid for -O2 option */ /* values specify one half-period and are only valid for -O2 option */
/* value = [period - 0.5us(160MHz) or 1.0us(80MHz)] * cycles per second / 2 */ /* value = [period - 0.5us(160MHz) or 1.0us(80MHz)] * cycles per second / 2 */
/* cycles per us = ca. 20 (80 MHz) / ca. 40 (160 MHz) */ /* cycles per us = ca. 20 (80 MHz) / ca. 40 (160 MHz) */
[I2C_SPEED_LOW] = {1990, 990}, /* 10 kbps (period 100 us) */ [I2C_SPEED_LOW] = {1990, 989}, /* 10 kbps (period 100 us) */
[I2C_SPEED_NORMAL] = { 190, 90}, /* 100 kbps (period 10 us) */ [I2C_SPEED_NORMAL] = { 190, 89}, /* 100 kbps (period 10 us) */
[I2C_SPEED_FAST] = { 40, 17}, /* 400 kbps (period 2.5 us) */ [I2C_SPEED_FAST] = { 40, 16}, /* 400 kbps (period 2.5 us) */
[I2C_SPEED_FAST_PLUS] = { 13, 0}, /* 1 Mbps (period 1 us) */ [I2C_SPEED_FAST_PLUS] = { 13, 0}, /* 1 Mbps (period 1 us) */
[I2C_SPEED_HIGH] = { 0, 0} /* 3.4 Mbps (period 0.3 us) is not working */ [I2C_SPEED_HIGH] = { 0, 0} /* 3.4 Mbps (period 0.3 us) is not working */
}; };
@ -115,12 +118,12 @@ static mutex_t i2c_bus_lock[I2C_NUMOF] = { MUTEX_INIT };
/* forward declaration of internal functions */ /* forward declaration of internal functions */
static inline void _i2c_delay (_i2c_bus_t* bus); static inline void _i2c_delay (_i2c_bus_t* bus);
static inline bool _i2c_read_scl (_i2c_bus_t* bus); static inline bool _i2c_scl_read (_i2c_bus_t* bus);
static inline bool _i2c_read_sda (_i2c_bus_t* bus); static inline bool _i2c_sda_read (_i2c_bus_t* bus);
static inline void _i2c_set_scl (_i2c_bus_t* bus); static inline void _i2c_scl_high (_i2c_bus_t* bus);
static inline void _i2c_clear_scl (_i2c_bus_t* bus); static inline void _i2c_scl_low (_i2c_bus_t* bus);
static inline void _i2c_set_sda (_i2c_bus_t* bus); static inline void _i2c_sda_high (_i2c_bus_t* bus);
static inline void _i2c_clear_sda (_i2c_bus_t* bus); static inline void _i2c_sda_low (_i2c_bus_t* bus);
static int _i2c_start_cond (_i2c_bus_t* bus); static int _i2c_start_cond (_i2c_bus_t* bus);
static int _i2c_stop_cond (_i2c_bus_t* bus); static int _i2c_stop_cond (_i2c_bus_t* bus);
static int _i2c_write_bit (_i2c_bus_t* bus, bool bit); static int _i2c_write_bit (_i2c_bus_t* bus, bool bit);
@ -129,6 +132,7 @@ static int _i2c_write_byte (_i2c_bus_t* bus, uint8_t byte);
static int _i2c_read_byte (_i2c_bus_t* bus, uint8_t* byte, bool ack); static int _i2c_read_byte (_i2c_bus_t* bus, uint8_t* byte, bool ack);
static int _i2c_arbitration_lost (_i2c_bus_t* bus, const char* func); static int _i2c_arbitration_lost (_i2c_bus_t* bus, const char* func);
static void _i2c_abort (_i2c_bus_t* bus, const char* func); static void _i2c_abort (_i2c_bus_t* bus, const char* func);
static void _i2c_clear (_i2c_bus_t* bus);
/* implementation of i2c interface */ /* implementation of i2c interface */
void i2c_init(i2c_t dev) void i2c_init(i2c_t dev)
@ -159,13 +163,30 @@ void i2c_init(i2c_t dev)
DEBUG ("%s: scl=%d sda=%d speed=%d\n", __func__, DEBUG ("%s: scl=%d sda=%d speed=%d\n", __func__,
_i2c_bus[dev].scl, _i2c_bus[dev].sda, _i2c_bus[dev].speed); _i2c_bus[dev].scl, _i2c_bus[dev].sda, _i2c_bus[dev].speed);
/* configure SDA and SCL pin as GPIO in open-drain mode with enabled pull-ups */ /*
gpio_init (_i2c_bus[dev].scl, GPIO_OD_PU); * Configure and initialize SDA and SCL pin.
gpio_init (_i2c_bus[dev].sda, GPIO_OD_PU); * Note: Due to critical timing required by the I2C software
* implementation, the ESP8266 GPIOs can not be used directly in GPIO_OD_PU
* mode. Instead, the GPIOs are configured in GPIO_IN_PU mode with
* open-drain output driver. Signal levels are then realized as following:
*
* - HIGH: The GPIO is used in the configured GPIO_IN_PU mode. In this
* mode, the output driver is in open-drain mode and pulled-up.
* - LOW : The GPIO is temporarily switched to GPIO_OD_PU mode. In this
* mode, the output value 0, which is written during
* initialization, actively drives the output to low.
*/
gpio_init (_i2c_bus[dev].scl, GPIO_IN_PU);
gpio_init (_i2c_bus[dev].sda, GPIO_IN_PU);
gpio_clear (_i2c_bus[dev].scl);
gpio_clear (_i2c_bus[dev].sda);
/* set SDA and SCL to be floating and pulled-up to high */ /* set SDA and SCL to be floating and pulled-up to high */
_i2c_set_sda (&_i2c_bus[dev]); _i2c_sda_high (&_i2c_bus[dev]);
_i2c_set_scl (&_i2c_bus[dev]); _i2c_scl_high (&_i2c_bus[dev]);
/* clear the bus if necessary (SDA is driven permanently low) */
_i2c_clear (&_i2c_bus[dev]);
i2c_release (dev); i2c_release (dev);
@ -243,7 +264,7 @@ int /* IRAM */ i2c_read_bytes(i2c_t dev, uint16_t addr, void *data, size_t len,
/* send STOP condition if I2C_NOSTOP flag is not set */ /* send STOP condition if I2C_NOSTOP flag is not set */
if (!(flags & I2C_NOSTOP)) { if (!(flags & I2C_NOSTOP)) {
_i2c_stop_cond (bus); res = _i2c_stop_cond (bus);
} }
return res; return res;
@ -304,7 +325,7 @@ int /* IRAM */ i2c_write_bytes(i2c_t dev, uint16_t addr, const void *data, size_
/* send STOP condition if I2C_NOSTOP flag is not set */ /* send STOP condition if I2C_NOSTOP flag is not set */
if (!(flags & I2C_NOSTOP)) { if (!(flags & I2C_NOSTOP)) {
return _i2c_stop_cond (bus); res = _i2c_stop_cond (bus);
} }
return res; return res;
@ -337,51 +358,98 @@ static inline void _i2c_delay (_i2c_bus_t* bus)
} }
/* /*
* Please note: SDA and SDL pins are used in GPIO_OD_PU mode * Note: Due to critical timing required by the I2C software implementation,
* (open-drain with pull-ups). * the ESP8266 GPIOs can not be used directly in GPIO_OD_PU mode. Instead,
* the GPIOs are configured in GPIO_IN_PU mode with open-drain output driver.
* Signal levels are then realized as following:
* *
* Setting a pin which is in open-drain mode leaves the pin floating and * - HIGH: The GPIO is used in the configured GPIO_IN_PU mode. In this mode,
* the signal is pulled up to high. The signal can then be actively driven * the output driver is in open-drain mode and pulled-up.
* to low by a slave. A read operation returns the current signal at the pin. * - LOW : The GPIO is temporarily switched to GPIO_OD_PU mode. In this mode,
* * the output value 0, which is written during initialization,
* Clearing a pin which is in open-drain mode actively drives the signal to * actively drives the output to low.
* low.
*/ */
static inline bool _i2c_read_scl(_i2c_bus_t* bus) static inline bool _i2c_scl_read(_i2c_bus_t* bus)
{ {
/* read SCL status (pin is in open-drain mode and set) */ /* read SCL status */
return GPIO.IN & bus->scl_bit; return GPIO.IN & bus->scl_bit;
} }
static inline bool _i2c_read_sda(_i2c_bus_t* bus) static inline bool _i2c_sda_read(_i2c_bus_t* bus)
{ {
/* read SDA status (pin is in open-drain mode and set) */ /* read SDA status */
return GPIO.IN & bus->sda_bit; return GPIO.IN & bus->sda_bit;
} }
static inline void _i2c_set_scl(_i2c_bus_t* bus) static inline void _i2c_scl_low(_i2c_bus_t* bus)
{ {
/* set SCL signal high (pin is in open-drain mode and pulled-up) */ /*
GPIO.OUT_SET = bus->scl_bit; * set SCL signal low (switch temporarily to GPIO_OD_PU where the
* written output value 0 drives the pin actively to low)
*/
GPIO.ENABLE_OUT_SET = bus->scl_bit;
} }
static inline void _i2c_clear_scl(_i2c_bus_t* bus) static inline void _i2c_scl_high(_i2c_bus_t* bus)
{ {
/* set SCL signal low (actively driven to low) */ /*
GPIO.OUT_CLEAR = bus->scl_bit; * set SCL signal high (switch back to GPIO_IN_PU mode, that is the pin is
* in open-drain mode and pulled-up to high)
*/
GPIO.ENABLE_OUT_CLEAR = bus->scl_bit;
} }
static inline void _i2c_set_sda(_i2c_bus_t* bus) static inline void _i2c_sda_low(_i2c_bus_t* bus)
{ {
/* set SDA signal high (pin is in open-drain mode and pulled-up) */ /*
GPIO.OUT_SET = bus->sda_bit; * set SDA signal low (switch temporarily to GPIO_OD_PU where the
* written output value 0 drives the pin actively to low)
*/
GPIO.ENABLE_OUT_SET = bus->sda_bit;
} }
static inline void _i2c_clear_sda(_i2c_bus_t* bus) static inline void _i2c_sda_high(_i2c_bus_t* bus)
{ {
/* set SDA signal low (actively driven to low) */ /*
GPIO.OUT_CLEAR = bus->sda_bit; * set SDA signal high (switch back to GPIO_IN_PU mode, that is the pin is
* in open-drain mode and pulled-up to high)
*/
GPIO.ENABLE_OUT_CLEAR = bus->sda_bit;
}
static void _i2c_clear(_i2c_bus_t* bus)
{
DEBUG("%s: dev=%u\n", __func__, bus->dev);
/**
* Sometimes a slave blocks and drives the SDA line permanently low.
* Send some clock pulses in that case (10 at maximum)
*/
/*
* If SDA is low while SCL is high for 10 half cycles, it is not an
* arbitration lost but a bus lock.
*/
int count = 10;
while (!_i2c_sda_read (bus) && _i2c_scl_read (bus) && count) {
count--;
_i2c_delay (bus);
}
if (count) {
/* was not a bus lock */
return;
}
/* send 10 clock pulses in case of bus lock */
count = 10;
while (!_i2c_sda_read (bus) && count--) {
_i2c_scl_low (bus);
_i2c_delay (bus);
_i2c_scl_high (bus);
_i2c_delay (bus);
}
} }
static void _i2c_abort(_i2c_bus_t* bus, const char* func) static void _i2c_abort(_i2c_bus_t* bus, const char* func)
@ -389,11 +457,14 @@ static void _i2c_abort(_i2c_bus_t* bus, const char* func)
DEBUG("%s: dev=%u\n", func, bus->dev); DEBUG("%s: dev=%u\n", func, bus->dev);
/* reset SCL and SDA to passive HIGH (floating and pulled-up) */ /* reset SCL and SDA to passive HIGH (floating and pulled-up) */
_i2c_set_sda (bus); _i2c_sda_high (bus);
_i2c_set_scl (bus); _i2c_scl_high (bus);
/* reset repeated start indicator */ /* reset repeated start indicator */
bus->started = false; bus->started = false;
/* clear the bus if necessary (SDA is driven permanently low) */
_i2c_clear(bus);
} }
static /* IRAM */ int _i2c_arbitration_lost (_i2c_bus_t* bus, const char* func) static /* IRAM */ int _i2c_arbitration_lost (_i2c_bus_t* bus, const char* func)
@ -401,12 +472,15 @@ static /* IRAM */ int _i2c_arbitration_lost (_i2c_bus_t* bus, const char* func)
DEBUG("%s: arbitration lost dev=%u\n", func, bus->dev); DEBUG("%s: arbitration lost dev=%u\n", func, bus->dev);
/* reset SCL and SDA to passive HIGH (floating and pulled-up) */ /* reset SCL and SDA to passive HIGH (floating and pulled-up) */
_i2c_set_sda (bus); _i2c_sda_high (bus);
_i2c_set_scl (bus); _i2c_scl_high (bus);
/* reset repeated start indicator */ /* reset repeated start indicator */
bus->started = false; bus->started = false;
/* clear the bus if necessary (SDA is driven permanently low) */
_i2c_clear(bus);
return -EAGAIN; return -EAGAIN;
} }
@ -424,17 +498,19 @@ static /* IRAM */ int _i2c_start_cond(_i2c_bus_t* bus)
/* prepare the repeated start condition */ /* prepare the repeated start condition */
/* SDA = passive HIGH (floating and pulled-up) */ /* SDA = passive HIGH (floating and pulled-up) */
_i2c_set_sda (bus); _i2c_sda_high (bus);
/* t_VD;DAT not neccessary */ /* t_VD;DAT not neccessary */
/* _i2c_delay (bus); */ /* _i2c_delay (bus); */
/* SCL = passive HIGH (floating and pulled-up) */ /* SCL = passive HIGH (floating and pulled-up) */
_i2c_set_scl (bus); _i2c_scl_high (bus);
/* clock stretching, wait as long as clock is driven to low by the slave */ /* clock stretching, wait as long as clock is driven to low by the slave */
uint32_t stretch = I2C_CLOCK_STRETCH; uint32_t stretch = I2C_CLOCK_STRETCH;
while (!_i2c_read_scl (bus) && stretch--) {} while (stretch && !_i2c_scl_read (bus)) {
stretch--;
}
if (stretch == 0) { if (stretch == 0) {
DEBUG("%s: clock stretching timeout dev=%u\n", __func__, bus->dev); DEBUG("%s: clock stretching timeout dev=%u\n", __func__, bus->dev);
res = -ETIMEDOUT; res = -ETIMEDOUT;
@ -446,12 +522,12 @@ static /* IRAM */ int _i2c_start_cond(_i2c_bus_t* bus)
} }
/* if SDA is low, arbitration is lost and someone else is driving the bus */ /* if SDA is low, arbitration is lost and someone else is driving the bus */
if (!_i2c_read_sda (bus)) { if (!_i2c_sda_read (bus)) {
return _i2c_arbitration_lost (bus, __func__); return _i2c_arbitration_lost (bus, __func__);
} }
/* begin the START condition: SDA = active LOW */ /* begin the START condition: SDA = active LOW */
_i2c_clear_sda (bus); _i2c_sda_low (bus);
/* wait t_HD;STA - hold time (repeated) START condition, */ /* wait t_HD;STA - hold time (repeated) START condition, */
/* max none */ /* max none */
@ -459,7 +535,7 @@ static /* IRAM */ int _i2c_start_cond(_i2c_bus_t* bus)
_i2c_delay (bus); _i2c_delay (bus);
/* complete the START condition: SCL = active LOW */ /* complete the START condition: SCL = active LOW */
_i2c_clear_scl (bus); _i2c_scl_low (bus);
/* needed for repeated start condition */ /* needed for repeated start condition */
bus->started = true; bus->started = true;
@ -478,18 +554,20 @@ static /* IRAM */ int _i2c_stop_cond(_i2c_bus_t* bus)
int res = 0; int res = 0;
/* begin the STOP condition: SDA = active LOW */ /* begin the STOP condition: SDA = active LOW */
_i2c_clear_sda (bus); _i2c_sda_low (bus);
/* wait t_LOW - LOW period of SCL clock */ /* wait t_LOW - LOW period of SCL clock */
/* min. in us: 4.7 (SM), 1.3 (FM), 0.5 (FPM), 0.16 (HSM); no max. */ /* min. in us: 4.7 (SM), 1.3 (FM), 0.5 (FPM), 0.16 (HSM); no max. */
_i2c_delay (bus); _i2c_delay (bus);
/* SCL = passive HIGH (floating and pulled up) while SDA = active LOW */ /* SCL = passive HIGH (floating and pulled up) while SDA = active LOW */
_i2c_set_scl (bus); _i2c_scl_high (bus);
/* clock stretching, wait as long as clock is driven to low by the slave */ /* clock stretching, wait as long as clock is driven to low by the slave */
uint32_t stretch = I2C_CLOCK_STRETCH; uint32_t stretch = I2C_CLOCK_STRETCH;
while (!_i2c_read_scl (bus) && stretch--) {} while (stretch && !_i2c_scl_read (bus)) {
stretch--;
}
if (stretch == 0) { if (stretch == 0) {
DEBUG("%s: clock stretching timeout dev=%u\n", __func__, bus->dev); DEBUG("%s: clock stretching timeout dev=%u\n", __func__, bus->dev);
res = -ETIMEDOUT; res = -ETIMEDOUT;
@ -500,7 +578,7 @@ static /* IRAM */ int _i2c_stop_cond(_i2c_bus_t* bus)
_i2c_delay (bus); _i2c_delay (bus);
/* complete the STOP condition: SDA = passive HIGH (floating and pulled up) */ /* complete the STOP condition: SDA = passive HIGH (floating and pulled up) */
_i2c_set_sda (bus); _i2c_sda_high (bus);
/* reset repeated start indicator */ /* reset repeated start indicator */
bus->started = false; bus->started = false;
@ -512,7 +590,7 @@ static /* IRAM */ int _i2c_stop_cond(_i2c_bus_t* bus)
_i2c_delay (bus); _i2c_delay (bus);
/* if SDA is low, arbitration is lost and someone else is driving the bus */ /* if SDA is low, arbitration is lost and someone else is driving the bus */
if (_i2c_read_sda (bus) == 0) { if (_i2c_sda_read (bus) == 0) {
return _i2c_arbitration_lost (bus, __func__); return _i2c_arbitration_lost (bus, __func__);
} }
@ -531,10 +609,10 @@ static /* IRAM */ int _i2c_write_bit (_i2c_bus_t* bus, bool bit)
/* SDA = bit */ /* SDA = bit */
if (bit) { if (bit) {
_i2c_set_sda (bus); _i2c_sda_high (bus);
} }
else { else {
_i2c_clear_sda (bus); _i2c_sda_low (bus);
} }
/* wait t_VD;DAT - data valid time (time until data are valid) */ /* wait t_VD;DAT - data valid time (time until data are valid) */
@ -542,7 +620,7 @@ static /* IRAM */ int _i2c_write_bit (_i2c_bus_t* bus, bool bit)
_i2c_delay (bus); _i2c_delay (bus);
/* SCL = passive HIGH (floating and pulled-up), SDA value is available */ /* SCL = passive HIGH (floating and pulled-up), SDA value is available */
_i2c_set_scl (bus); _i2c_scl_high (bus);
/* wait t_HIGH - time for the slave to read SDA */ /* wait t_HIGH - time for the slave to read SDA */
/* min. in us: 4 (SM), 0.6 (FM), 0.26 (FPM), 0.09 (HSM); no max. */ /* min. in us: 4 (SM), 0.6 (FM), 0.26 (FPM), 0.09 (HSM); no max. */
@ -550,7 +628,9 @@ static /* IRAM */ int _i2c_write_bit (_i2c_bus_t* bus, bool bit)
/* clock stretching, wait as long as clock is driven low by the slave */ /* clock stretching, wait as long as clock is driven low by the slave */
uint32_t stretch = I2C_CLOCK_STRETCH; uint32_t stretch = I2C_CLOCK_STRETCH;
while (!_i2c_read_scl (bus) && stretch--) {} while (stretch && !_i2c_scl_read (bus)) {
stretch--;
}
if (stretch == 0) { if (stretch == 0) {
DEBUG("%s: clock stretching timeout dev=%u\n", __func__, bus->dev); DEBUG("%s: clock stretching timeout dev=%u\n", __func__, bus->dev);
res = -ETIMEDOUT; res = -ETIMEDOUT;
@ -558,12 +638,12 @@ static /* IRAM */ int _i2c_write_bit (_i2c_bus_t* bus, bool bit)
/* if SCL is high, now data is valid */ /* if SCL is high, now data is valid */
/* if SDA is high, check that nobody else is driving SDA low */ /* if SDA is high, check that nobody else is driving SDA low */
if (bit && !_i2c_read_sda(bus)) { if (bit && !_i2c_sda_read(bus)) {
return _i2c_arbitration_lost (bus, __func__); return _i2c_arbitration_lost (bus, __func__);
} }
/* SCL = active LOW to allow next SDA change */ /* SCL = active LOW to allow next SDA change */
_i2c_clear_scl(bus); _i2c_scl_low(bus);
return res; return res;
} }
@ -578,18 +658,20 @@ static /* IRAM */ int _i2c_read_bit (_i2c_bus_t* bus, bool* bit)
int res = 0; int res = 0;
/* SDA = passive HIGH (floating and pulled-up) to let the slave drive data */ /* SDA = passive HIGH (floating and pulled-up) to let the slave drive data */
_i2c_set_sda (bus); _i2c_sda_high (bus);
/* wait t_VD;DAT - data valid time (time until data are valid) */ /* wait t_VD;DAT - data valid time (time until data are valid) */
/* max. in us: 3.45 (SM), 0.9 (FM), 0.45 (FPM); no min */ /* max. in us: 3.45 (SM), 0.9 (FM), 0.45 (FPM); no min */
_i2c_delay (bus); _i2c_delay (bus);
/* SCL = passive HIGH (floating and pulled-up), SDA value is available */ /* SCL = passive HIGH (floating and pulled-up), SDA value is available */
_i2c_set_scl (bus); _i2c_scl_high (bus);
/* clock stretching, wait as long as clock is driven to low by the slave */ /* clock stretching, wait as long as clock is driven to low by the slave */
uint32_t stretch = I2C_CLOCK_STRETCH; uint32_t stretch = I2C_CLOCK_STRETCH;
while (!_i2c_read_scl (bus) && stretch--) {} while (stretch && !_i2c_scl_read (bus)) {
stretch--;
}
if (stretch == 0) { if (stretch == 0) {
DEBUG("%s: clock stretching timeout dev=%u\n", __func__, bus->dev); DEBUG("%s: clock stretching timeout dev=%u\n", __func__, bus->dev);
res = -ETIMEDOUT; res = -ETIMEDOUT;
@ -600,10 +682,10 @@ static /* IRAM */ int _i2c_read_bit (_i2c_bus_t* bus, bool* bit)
_i2c_delay (bus); _i2c_delay (bus);
/* SCL is high, read out bit */ /* SCL is high, read out bit */
*bit = _i2c_read_sda (bus); *bit = _i2c_sda_read (bus);
/* SCL = active LOW to allow next SDA change */ /* SCL = active LOW to allow next SDA change */
_i2c_clear_scl(bus); _i2c_scl_low(bus);
return res; return res;
} }