54 lines
1.7 KiB
C++
54 lines
1.7 KiB
C++
#include <FreeRTOSVariant.h>
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/*
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* Formula for the frequency is:
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* f = F_CPU / (PRESCALER * (1 + COUNTER_TOP)
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*
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* Assuming the MCU clock of 16MHz, prescaler 1024 and counter top 249, the resulting tick period is 16 ms (62.5 Hz).
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*/
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#define TICK_PERIOD_16MS 249
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#define PRESCALER 1024
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#if (portTICK_PERIOD_MS != (PRESCALER * (1 + TICK_PERIOD_16MS) * 1000 / F_CPU))
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#warning portTICK_PERIOD_MS defined in FreeRTOSVariant.h differs from your timer configuration
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#endif
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// For register TCCR0A:
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#define NO_PWM (0 << COM0A1) | (0 << COM0A0) | (0 << COM0B1) | (0 << COM0B0)
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#define MODE_CTC_TCCR0A (1 << WGM01) | (0 << WGM00)
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// For register TCCR0B:
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#define MODE_CTC_TCCR0B (0 << WGM02)
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#define PRESCALER_1024 (1 << CS02) | (0 << CS01) | (1 << CS00)
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// For register TIMSK0:
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#define INTERRUPT_AT_TOP (1 << OCIE0A)
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extern "C"
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// todo удалить файл?
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void prvSetupTimerInterrupt( void )
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{
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// In case Arduino platform has pre-configured the timer,
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// disable it before re-configuring here to avoid unpredicted results:
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TIMSK0 = 0;
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// Now configure the timer:
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TCCR0A = NO_PWM | MODE_CTC_TCCR0A;
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TCCR0B = MODE_CTC_TCCR0B | PRESCALER_1024;
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OCR0A = TICK_PERIOD_16MS;
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// Prevent missing the top and going into a possibly long wait until wrapping around:
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TCNT0 = 0;
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// At this point the global interrupt flag is NOT YET enabled,
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// so you're NOT starting to get the ISR calls until FreeRTOS enables it just before launching the scheduler.
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TIMSK0 = INTERRUPT_AT_TOP;
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}
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ISR(TIMER0_COMPA_vect, ISR_NAKED) __attribute__ ((hot, flatten));
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ISR(TIMER0_COMPA_vect)
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{
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vPortYieldFromTick();
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__asm__ __volatile__ ( "reti" );
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}
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