Interrupt

Periodic Query of Status Information (Polling)

• Synchronous with main programm
• Advantages
  • Simple and straightforward
  • Implicit synchronization
  • Deterministic
  • No additional interrupt logic required
• Disadvantages
  • Busy wait (wastes CPU time)
  • Reduced trhoughput
  • Long reaction times

if (spi_is_txe_set()) {
	spi_write_data(...);
}

if (uar_is_rxne_set()) {
	uard_data = uart_read_data();
}

if (adc_is_eoc()) {
	adc+data = adc_read_data();
}

Interrupt Driven I/O

Interrupt Performance

• tISR > "Time between two interrupt events"
  • Some interrupt events will not be serviced (lost)
    • Data will be lost
  • fINT as well as tISR may vary over time
    • Average may be ok, but individual interrupt events may still be lost

Impact on system performance

$$\text{Impact}={\text{f}}_{INT}\ast {\text{t}}_{ISR}\ast 100$$

Keyboard

Unit Converter

tISR = 6 us = 0,000006s fInt=20Hz = 20 1/s

Impact = 20 Hz * 6us * 100% = 0.012%

Interrupt Priorities

Code

void TIM2_IRQHandler(void)
{
}

/**
 * \brief  Timer 3 ISR: Generating load
 */
void TIM3_IRQHandler(void)
{
    hal_timer_irq_clear(TIM3, HAL_TIMER_IRQ_UE);
    tim3_interrupt_counter++;
}