timer-test.cpp

#include <Arduino.h>

#define clk 10 // PWM Clock Pin - First timer, first channel
#define testpin 9

uint32_t count = 0;

// Timer stuff
IRQ_NUMBER_t irq = IRQ_QTIMER1;
IMXRT_TMR_t* tmr = &IMXRT_TMR1;
IMXRT_TMR_CH_t* ch0 = &tmr->CH[0];

void isr() {
    digitalWrite(testpin, HIGH);
    count++;
    delayMicroseconds(250);
    digitalWrite(testpin, LOW);
    ch0->CSCTRL &= ~TMR_CSCTRL_TCF1;
}

void timerSetup() {
    ch0->CTRL = 0x0000;
    attachInterruptVector(irq, isr);
    NVIC_ENABLE_IRQ(irq);

    int period = 1'000; // Period in us
    int psc = 2; // Prescaler 2^(n-1)
    float pscValue = 1 << (psc & 0b0111);
    uint32_t pscBits = 0b1000 | (psc & 0b0111);

    float t = period * (150.0f / pscValue); // Number of clock cycles per period
    uint16_t reload;
    if(t > 0xFFFF) reload = 0xFFFE;
    else reload = (uint16_t)t - 1;

    ch0->CTRL = 0x0000;
    ch0->LOAD = 0x0000;
    ch0->COMP1 = reload;
    ch0->CMPLD1 = reload;
    ch0->CNTR = 0x0000;
    ch0->CSCTRL &= ~TMR_CSCTRL_TCF1;
    ch0->CSCTRL |= TMR_CSCTRL_TCF1EN;

    ch0->CTRL = TMR_CTRL_CM(1) | TMR_CTRL_PCS(pscBits) | 
        TMR_CTRL_LENGTH;
}

void setup() {
    pinMode(LED_BUILTIN, OUTPUT);
    pinMode(testpin, OUTPUT);
    digitalWrite(LED_BUILTIN, HIGH);
    delay(1000);

    Serial.begin(115200);
    while(!Serial);

    Serial.println("Serial initialized.");

    timerSetup();

    Serial.println("Setup done");
    digitalWrite(LED_BUILTIN, LOW);
    interrupts(); noInterrupts();
}

void loop() {
    count = 0;
    interrupts();
    while(count < 100) {
        //Serial.print(" ");
    }
    noInterrupts();
    Serial.println();
    Serial.print("Count: ");
    Serial.println(count);
    delay(1000);
}