Arduino_FreeRTOS_Library/doc/tick_sources_timer0.cpp at master · feilipu/Arduino_FreeRTOS_Library · GitHub

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#include <FreeRTOSVariant.h>

* Formula for the frequency is:

* f = F_CPU / (PRESCALER * (1 + COUNTER_TOP)

* Assuming the MCU clock of 16MHz, prescaler 1024 and counter top 249, the resulting tick period is 16 ms (62.5 Hz).

#define TICK_PERIOD_16MS 249

#define PRESCALER 1024

#if (portTICK_PERIOD_MS != (PRESCALER * (1 + TICK_PERIOD_16MS) * 1000 / F_CPU))

#warning portTICK_PERIOD_MS defined in FreeRTOSVariant.h differs from your timer configuration

#endif

// For register TCCR0A:

#define NO_PWM (0 << COM0A1) | (0 << COM0A0) | (0 << COM0B1) | (0 << COM0B0)

#define MODE_CTC_TCCR0A (1 << WGM01) | (0 << WGM00)

// For register TCCR0B:

#define MODE_CTC_TCCR0B (0 << WGM02)

#define PRESCALER_1024 (1 << CS02) | (0 << CS01) | (1 << CS00)

// For register TIMSK0:

#define INTERRUPT_AT_TOP (1 << OCIE0A)

extern "C"

void prvSetupTimerInterrupt( void )

{

// In case Arduino platform has pre-configured the timer,

// disable it before re-configuring here to avoid unpredicted results:

TIMSK0 = 0;

// Now configure the timer:

TCCR0A = NO_PWM | MODE_CTC_TCCR0A;

TCCR0B = MODE_CTC_TCCR0B | PRESCALER_1024;

OCR0A = TICK_PERIOD_16MS;

// Prevent missing the top and going into a possibly long wait until wrapping around:

TCNT0 = 0;

// At this point the global interrupt flag is NOT YET enabled,

// so you're NOT starting to get the ISR calls until FreeRTOS enables it just before launching the scheduler.

TIMSK0 = INTERRUPT_AT_TOP;

}

ISR(TIMER0_COMPA_vect, ISR_NAKED) __attribute__ ((hot, flatten));

ISR(TIMER0_COMPA_vect)

{

vPortYieldFromTick();

__asm__ __volatile__ ( "reti" );

}

Arduino_FreeRTOS_Library/doc/tick_sources_timer0.cpp at master · feilipu/Arduino_FreeRTOS_Library · GitHub

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