AVR Freaks

I wrote a short test program which starts a IRQ handler on each falling edge on a GPIO input pin.

After struggling with some parameters in the ioport and pio ASF functions used to configure the IRQ handler and GPIO pin I finally got as best result a 4µs delay between input pin signal change and IRQ handler start. I am using a scope for measurement.

This is quite a long time for a 300MHz embedded MCU which is optimized for fast interrupt handling I think. I know that there is some code executed in front of the handler due to the PIO handler and FPU support but, well.... I'm stuck here.

// "/INT" pin
#define PIN_NOT_INT_GPIO      (PIO_PA6_IDX)
#define PIN_NOT_INT_FLAGS     (IOPORT_MODE_PULLUP | IOPORT_MODE_GLITCH_FILTER)
#define PIN_NOT_INT_SENSE     (IOPORT_SENSE_FALLING)

#define PIN_NOT_INT_MASK  PIO_PA6
#define PIN_NOT_INT_PIO   PIOA
#define PIN_NOT_INT_ID    ID_PIOA
#define PIN_NOT_INT_ATTR  (PIO_PULLUP | PIO_DEGLITCH | PIO_IT_FALL_EDGE)
#define PIN_NOT_INT_IRQn  PIOA_IRQn


#define PEAK_CURR_IRQ_PRIOR_PIO    0x00		// highest priority


static void PeakCurrentIrq_Handler(uint32_t id, uint32_t mask)
{
	// signal IRQ handler function entry on digital output
	ioport_set_pin_level(PIN_TEST1_GPIO, IOPORT_PIN_LEVEL_HIGH);

	// clear and re-init interrupt
	uint32_t bitmask = pio_get_interrupt_mask(PIN_NOT_INT_PIO);
	pio_disable_interrupt(PIN_NOT_INT_PIO, 0xFFFFFFFF);
	pio_get_interrupt_status(PIN_NOT_INT_PIO);
	NVIC_DisableIRQ((IRQn_Type) PIN_NOT_INT_ID);

	; // do what has to be done

	NVIC_ClearPendingIRQ((IRQn_Type) PIN_NOT_INT_ID);
	NVIC_SetPriority((IRQn_Type) PIN_NOT_INT_ID, PEAK_CURR_IRQ_PRIOR_PIO);
	NVIC_EnableIRQ((IRQn_Type) PIN_NOT_INT_ID);
	pio_enable_interrupt(PIN_NOT_INT_PIO, bitmask);


	// signal IRQ handler function exit on digital output
	ioport_set_pin_level(PIN_TEST1_GPIO, IOPORT_PIN_LEVEL_LOW);

	return;
}


static void enable_peak_irq(void)
{
	pmc_enable_periph_clk(PIN_NOT_INT_ID);
	/* Interrupt on falling edge  */
	pio_handler_set(PIN_NOT_INT_PIO, PIN_NOT_INT_ID, PIN_NOT_INT_MASK, PIN_NOT_INT_ATTR, PeakCurrentIrq_Handler);
	pio_handler_set_priority(PIN_NOT_INT_PIO, (IRQn_Type) PIN_NOT_INT_ID, PEAK_CURR_IRQ_PRIOR_PIO);
}

int main(void)
{
	/* Initialize the SAM system. */
	sysclk_init();
	board_init();

	ioport_set_pin_input_mode(PIN_NOT_INT_GPIO, PIN_NOT_INT_FLAGS, PIN_NOT_INT_SENSE);

	// enable peak current detection
	enable_peak_irq();

	while(1)
	{
		// pull IRQ input pin low to run IRQ handler
		ioport_set_pin_level(PIN_D4_GPIO, IOPORT_PIN_LEVEL_LOW);

		delay_ms(1);
		
		// set IRQ input pin high
		ioport_set_pin_level(PIN_D4_GPIO, IOPORT_PIN_LEVEL_HIGH);

		delay_ms(1);
	}
}

PIN_D4_GPIO is physically connected to the IRQ input pin PIN_NOT_INT_GPIO and is used to trigger the scope.
PIN_TEST1_GPIO is an output used for timing measurement.
Trivial initialization code of these two pins is not shown here in this example.

Has anyone any experience / results / ideas on that topic ?

P.S:

PIN_D4_GPIO is physically connected to the IRQ input pin PIN_NOT_INT_GPIO and is used to trigger the scope.
PIN_TEST1_GPIO is an output used for timing measurement.
Trivial initialization code of these two pins is not shown here in this example.