3. API Changes for XMega

A few APIs have changed, out of necessity, to support the XMega.

void attachInterrupt(port, callback, mode);   (modified)

  port is the I/O port and int number
  example: PORTC_INT0, PORTD_INT0, PORTR_INT1, etc.

  callback is a pointer to a user callback function

  mode (new) is a bit-flag indicating the following:
    trigger mode - LOW, HIGH, RISING, FALLING, CHANGE
    interrupt pin - INT_MODE_PIN_DEFAULT, INT_MODE_PIN0, etc.
    priority - INT_MODE_PRI_DEFAULT, INT_MODE_PRI_HIGH, etc.

typical usage:
    attachInterrupt(PORTD_INT0,
                          my_callback,
                          RISING
                          | INT_MODE_PIN_DEFAULT
                          | INT_MODE_PRI_DEFAULT);

The port (formerly 'interrupt number') is passed to 'detachInterrupt' and detaches ALL interrupts for that particular port and interrupt combination. Some CPUs have 2 interrupts per port, some only one. The first will be labeled 'INT0', and subsequent interrupts 'INT1', etc. Each port+interrupt combination can only have a single callback, so you should assign the callback and all of the interrupt pins at the same time. It will be up to the callback functino to determine which pins is responsible for the interrupt.

There is a small exception with hardware flow control, which manages its interrupts separately, in conjuction with 'attachInterrupt()' and 'detachInterrupt()' calls. It is possible to assign an interrupt on the same port as the hardware flow control pins, without interfering. However, its priority will not be lowered from 'HIGH'.

uint8_t readCalibrationData(iIndex);   (new)

  iIndex is the index within the 'calibration data' to be read

This function reads the 'calibration data', which is assigned by the manufacturer to contain the calibration data necessary for certain functions. This also includes CPU identification information that can be used to uniquely identify the processor. One practical use is found in setting up the A:D converter, by reading the calibration data and assigning it to the 'CAL' register for the A:D converter during setup.

void adc_setup(void);   (new)

This function should be called whenever you exit from 'sleep' mode to re-assign the correct values to the A:D converter. On the XMega, sleep mode pretty much clears the slate for all peripherals. Serial ports and other peripherals are automatically initialized by 'Start' and similar member functions. But for the A:D converter, there was no official way to reset it. So this function was added.

typical usage:

// interrupt callback for 'wake-up'
void wake_up(void)
{
  sleep_disable(); // must do this
  detachInterrupt(PORTC_INT0);
}

  ...

  // serial port shutdown
  Serial.end();
  Serial2.end();
  set_sleep_mode(SLEEP_MODE_EXT_STANDBY);
  // wake up with LOW level on PORTC pin 2
  attachInterrupt(PORTC_INT0, wake_up, LOW);
  // disable interrupts - see avr/sleep.h
  cli();
  power_all_disable();
  sleep_enable(); // only if ints are off
  // optionally disable BOD while sleeping
  #ifdef sleep_bod_disable
  sleep_bod_disable();
  #endif

  sei(); // enable interrupts
  sleep_cpu();

  // when I awake, I'll be here
  sleep_disable(); // make sure
  sei(); // ints on (make sure)
  power_all_enable(); // see avr/power.h

  ...

  adc_setup(); // re-init A:D