DigitalIOExamples/PeriodicInterrupt/PeriodicInterrupt.cpp

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/*
 * PeriodicInterrupt
 * Configure a user-defined periodic interrupt.
 */
 /*
 * Title: PeriodicInterrupt
 *
 * Objective:
 *    This example demonstrates how to generate a user defined periodic
 * interrupt.
 *
 * Description:
 *    This example configures a periodic interrupt handler that turns the
 * user LED on and off during each call to the interrupt. Once configured,
 * The interrupt will execute at the requested frequency without having to
 * be called from the main program.
 *
 * Requirements:
 * ** None
 *
 * Links:
 * ** ClearCore Documentation: https://teknic-inc.github.io/ClearCore-library/
 * ** ClearCore Manual: https://www.teknic.com/files/downloads/clearcore_user_manual.pdf
 *
 * Last Modified: 6/11/2020
 * Copyright (c) 2020 Teknic Inc. This work is free to use, copy and distribute under the terms of
 * the standard MIT permissive software license which can be found at https://opensource.org/licenses/MIT
 */

#include "ClearCore.h"

void ConfigurePeriodicInterrupt(uint32_t frequencyHz);

extern "C" void TCC2_0_Handler(void) __attribute__((
            alias("PeriodicInterrupt")));

// Periodic interrupt priority
// 0 is highest priority, 7 is lowest priority
// Recommended priority is >= 4 to not interfere with other processing
#define PERIODIC_INTERRUPT_PRIORITY     4
#define ACK_PERIODIC_INTERRUPT  TCC2->INTFLAG.reg = TCC_INTFLAG_MASK

// State currently written to LED_BUILTIN
bool ledState = false;
uint32_t interruptFreqHz = 4;

extern "C" void PeriodicInterrupt(void) {
    // Perform periodic processing here.
    ledState = !ledState;
    ConnectorLed.State(ledState);

    // Acknowledge the interrupt to clear the flag and wait for the next interrupt.
    ACK_PERIODIC_INTERRUPT;
}

int main() {
    ConfigurePeriodicInterrupt(interruptFreqHz);
}

void ConfigurePeriodicInterrupt(uint32_t frequencyHz) {
    // Enable the TCC2 peripheral.
    // TCC2 and TCC3 share their clock configuration and they
    // are already configured to be clocked at 120 MHz from GCLK0.
    CLOCK_ENABLE(APBCMASK, TCC2_);

    // Disable TCC2.
    TCC2->CTRLA.bit.ENABLE = 0;
    SYNCBUSY_WAIT(TCC2, TCC_SYNCBUSY_ENABLE);

    // Reset the TCC module so we know we are starting from a clean state.
    TCC2->CTRLA.bit.SWRST = 1;
    while (TCC2->CTRLA.bit.SWRST) {
        continue;
    }

    // If the frequency requested is zero, disable the interrupt and bail out.
    if (!frequencyHz) {
        NVIC_DisableIRQ(TCC2_0_IRQn);
        return;
    }

    // Determine the clock prescaler and period value needed to achieve the
    // requested frequency.
    uint32_t period = (CPU_CLK + frequencyHz / 2) / frequencyHz;
    uint8_t prescale;
    // Make sure period is >= 1.
    period = max(period, 1U);

    // Prescale values 0-4 map to prescale divisors of 1-16,
    // dividing by 2 each increment.
    for (prescale = TCC_CTRLA_PRESCALER_DIV1_Val;
            prescale < TCC_CTRLA_PRESCALER_DIV16_Val && (period - 1) > UINT16_MAX;
            prescale++) {
        period = period >> 1;
    }
    // Prescale values 5-7 map to prescale divisors of 64-1024,
    // dividing by 4 each increment.
    for (; prescale < TCC_CTRLA_PRESCALER_DIV1024_Val && (period - 1) > UINT16_MAX;
            prescale++) {
        period = period >> 2;
    }
    // If we have maxed out the prescaler and the period is still too big,
    // use the maximum period. This results in a ~1.788 Hz interrupt.
    if (period > UINT16_MAX) {
        TCC2->PER.reg = UINT16_MAX;
    }
    else {
        TCC2->PER.reg = period - 1;
    }
    TCC2->CTRLA.bit.PRESCALER = prescale;

    // Interrupt every period on counter overflow.
    TCC2->INTENSET.bit.OVF = 1;
    // Enable TCC2.
    TCC2->CTRLA.bit.ENABLE = 1;

    // Set the interrupt priority and enable it.
    NVIC_SetPriority(TCC2_0_IRQn, PERIODIC_INTERRUPT_PRIORITY);
    NVIC_EnableIRQ(TCC2_0_IRQn);
}