MSP432P401R: Timer A - Capture Mode for ultrasonic sensor HC-SR04

Part Number: MSP432P401R

Hello,

I need to configure the Timer A in capture mode to measure the echo pulse of the HC-SR04 sensor i'm using.

I'm sending a 10us pulse to the sensor (i tried less and more just in case but same results) and I'm waiting for the echo that should trigger my interruption, but that's not the case. When I force the capture pin (P2.4) to 3.3V and then to 0V, my breakpoints in the interruption are triggered correctly.

I really don't understand what's wrong with my code. There might be some error in my code that i'm not seeing.

By the way, my sensor is working since I tested it with a code for Energia, but i want to use CCS and the driverlib.

#include "driverlib.h"
#include <stdint.h>

/* Timer_A Continuous Mode Configuration Parameter */
const Timer_A_ContinuousModeConfig continuousModeConfig =
{
        TIMER_A_CLOCKSOURCE_SMCLK,           // SMCLK Clock Source
        TIMER_A_CLOCKSOURCE_DIVIDER_1,       // SMCLK/1 = 3MHz
        TIMER_A_TAIE_INTERRUPT_DISABLE,      // Disable Timer ISR
        TIMER_A_SKIP_CLEAR                   // Skup Clear Counter
};

/* Timer_A Capture Mode Configuration Parameter */
const Timer_A_CaptureModeConfig captureModeConfig =
{
        TIMER_A_CAPTURECOMPARE_REGISTER_1,        // CC Register 2
		TIMER_A_CAPTUREMODE_RISING_EDGE,          // Rising Edge and falling
        TIMER_A_CAPTURE_INPUTSELECT_CCIxA,        // CCIxA Input Select
        TIMER_A_CAPTURE_SYNCHRONOUS,              // Synchronized Capture
        TIMER_A_CAPTURECOMPARE_INTERRUPT_ENABLE,  // Enable interrupt
        TIMER_A_OUTPUTMODE_OUTBITVALUE            // Output bit value
};

static void Delay(uint32_t loop)
{
    volatile uint32_t i;

    for (i = 0 ; i < loop ; i++);
}

int meas1 = 0;
int meas2 = 0;
int main(void)
{
	/* Stop watchdog timer */
	MAP_WDT_A_holdTimer();

	CS_setDCOCenteredFrequency(CS_DCO_FREQUENCY_24);                    // 24000000 Hz

	CS_initClockSignal(CS_MCLK,  CS_DCOCLK_SELECT, CS_CLOCK_DIVIDER_1); // 24000000 Hz
	CS_initClockSignal(CS_SMCLK, CS_DCOCLK_SELECT, CS_CLOCK_DIVIDER_8); //  3000000 Hz

	/* Configuring P2.4 as peripheral input for capture */
	GPIO_setAsPeripheralModuleFunctionOutputPin(GPIO_PORT_P2, GPIO_PIN4,
		GPIO_PRIMARY_MODULE_FUNCTION);
	GPIO_setAsOutputPin(GPIO_PORT_P1, GPIO_PIN5);

	/* Configuring Capture Mode */
	Timer_A_initCapture(TIMER_A0_BASE, &captureModeConfig);

	/* Configuring Continuous Mode */
	Timer_A_configureContinuousMode(TIMER_A0_BASE, &continuousModeConfig);

	/* Enabling interrupts */
	Interrupt_enableInterrupt(INT_TA0_N);
	Interrupt_enableMaster();

	/* Starting the Timer32 */
	Timer32_initModule(TIMER32_0_BASE, TIMER32_PRESCALER_1, TIMER32_32BIT, TIMER32_PERIODIC_MODE);
	Timer32_disableInterrupt(TIMER32_0_BASE);
	Timer32_setCount(TIMER32_0_BASE, 1);
	Timer32_startTimer(TIMER32_0_BASE, true);

	/* Starting the Timer_A0 in continuous mode */
	Timer_A_startCounter(TIMER_A0_BASE, TIMER_A_CONTINUOUS_MODE);
	while(1)
	{
		GPIO_setOutputHighOnPin(GPIO_PORT_P1, GPIO_PIN5);
	    Timer32_setCount(TIMER32_0_BASE, 24 * 10);
		while (Timer32_getValue(TIMER32_0_BASE) > 0); // Wait 10us
		GPIO_setOutputLowOnPin(GPIO_PORT_P1, GPIO_PIN5);
                //software delays
		Delay(40000);
		Delay(40000);
		Delay(40000);
		Delay(40000);
		Delay(40000);
		Delay(40000);
		Delay(40000);
		Delay(40000);
		Delay(40000);
		Delay(40000);
		Delay(40000);
		Delay(40000);
		Delay(40000);
		Delay(40000);
		Delay(40000);
	}
}

void TA0_N_IRQHandler(void)
{
    int rising  = 0;

    Timer_A_clearCaptureCompareInterrupt(TIMER_A0_BASE,
            TIMER_A_CAPTURECOMPARE_REGISTER_1);

    if(P2IN&0x10) rising=1; else rising=0;

    if(rising) // Start
    {
    	meas1 = Timer_A_getCaptureCompareCount(TIMER_A0_BASE, TIMER_A_CAPTURECOMPARE_REGISTER_1);
    }
    else
    {
    	meas2 = Timer_A_getCaptureCompareCount(TIMER_A0_BASE, TIMER_A_CAPTURECOMPARE_REGISTER_1);
    }
}

Thanks,

Olivier