SPI Hardware Chip Select, how to use?

[Greg Corson]

I've got some SPI code that works, flipping the CS pin manually. I'd like to see how the "hardware chip select" feature performs but I can't get it to work. I've been hunting for example code but can't find any.

I setup SPI like this

Code: Select all

  ICM40605_SPI->begin(ICM40605_SCK, ICM40605_MISO, ICM40605_MOSI, ICM40605_CS);
  ICM40605_SPI->beginTransaction(SPISettings(SPI_FREQUENCY, MSBFIRST, SPI_MODE3));
  delay(100);
  ICM40605_SPI->setHwCs(true);

And a typical read looks like this

Code: Select all

void readRegister(uint8_t* output, uint8_t offset) {
    uint8_t result = 0;

//    digitalWrite(ICM40605_CS, LOW);
    ICM40605_SPI->transfer(offset | 0x80);

    result = ICM40605_SPI->transfer(0x00);

//    digitalWrite(ICM40605_CS, HIGH);
    
    *output = result;
}

If I leave out the setHwCs and uncomment the "digitalWrite" statements, everything works fine. In the configuration above the CS line goes high when I do the transfer, but there is no spi clock and the CS never goes back down.

What am I missing?