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manually handle AVR i2c setspeed to handle slow clocks #104

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Merged
merged 2 commits into from
Jul 31, 2022
Merged

manually handle AVR i2c setspeed to handle slow clocks #104

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36da2e4
prescaler is not calculated here https://github.com/arduino/ArduinoCo…
ladyada Jul 31, 2022
3e0e740
clang
ladyada Jul 31, 2022
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33 changes: 32 additions & 1 deletion Adafruit_I2CDevice.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -259,9 +259,40 @@ uint8_t Adafruit_I2CDevice::address(void) { return _addr; }
* Not necessarily that the speed was achieved!
*/
bool Adafruit_I2CDevice::setSpeed(uint32_t desiredclk) {
#if (ARDUINO >= 157) && !defined(ARDUINO_STM32_FEATHER) && !defined(TinyWireM_h)
#if defined(__AVR__) // fix arduino core set clock
// calculate TWBR correctly
uint8_t prescaler = 1;
uint32_t atwbr = ((F_CPU / desiredclk) - 16) / 2;
if (atwbr <= 255) {
prescaler = 1;
TWSR = 0x0;
} else if (atwbr <= 1020) {
atwbr /= 4;
prescaler = 4;
TWSR = 0x1;
} else if (atwbr <= 4080) {
atwbr /= 16;
prescaler = 16;
TWSR = 0x2;
} else if (atwbr <= 16320) {
atwbr /= 64;
prescaler = 64;
TWSR = 0x3;
}
#ifdef DEBUG_SERIAL
Serial.print(F("TWSR prescaler = "));
Serial.println(prescaler);
Serial.print(F("TWBR = "));
Serial.println(atwbr);
#endif
TWBR = atwbr;
return true;

#elif (ARDUINO >= 157) && !defined(ARDUINO_STM32_FEATHER) && \
!defined(TinyWireM_h)
_wire->setClock(desiredclk);
return true;

#else
(void)desiredclk;
return false;
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