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prescaler is not calculated here https://github.com/arduino/ArduinoCore-avr/blob/master/libraries/Wire/src/utility/twi.c#L139 which means we cannot get below 30.5mhz!

This commit is contained in:
lady ada 2022-07-31 17:04:44 -04:00
parent c421326131
commit 36da2e4611
1 changed files with 29 additions and 1 deletions
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30
Adafruit_I2CDevice.cpp
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@ -259,9 +259,37 @@ 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;