timer_a_ex4_periodCapture.c

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/*******************************************************************************
 * MSP430i2xx Timer_A - Period Capture
 *
 * Description: In this example, the 16 bit Timer_A is configured to capture
 * the period of an incoming signal. For this example ACLK is looped back to
 * the Timer_A capture pin to provide an example source. When the input clock
 * signal goes from low to high the capture interrupt fires and the current
 * value of the timer is stored in an array for data logging. To determine the
 * period of the clock source simply subtract two adjacent capture values to
 * get the number of ticks between their rising edges.
 *
 * In our example the input clock source is ACLK running at 32kHz. Timer_A is
 * using SMCLK for sampling the data which runs at 16.384MHz or 61.04ns. The
 * difference between samples is 512 meaning the input clock source has a
 * period of 512 * 61.04ns = 31.25us or 32kHz. Once enough data captures have
 * occurred the device blinks the LED indicating the data is ready.
 *
 *                MSP430i2041
 *             ------------------
 *         /|\|                  |
 *          | |              P1.4|--->LED
 *          --|RST               |
 *            |         P1.5/CC1A|<---|
 *            |                  |    |
 *            |         P1.2/ACLK|--->|
 *            |                  |
 *
 *
 * Author: Zack Lalanne
 ******************************************************************************/
#include "driverlib.h"
 
#define NUMBER_OF_CAPTURES  50
 
uint16_t CaptureData[NUMBER_OF_CAPTURES];
uint16_t CaptureDataIndex = 0;
 
int main(void) {
 
    Timer_A_initCaptureModeParam captureModeConfig = {
        TIMER_A_CAPTURECOMPARE_REGISTER_1,        // CC Register 1
        TIMER_A_CAPTUREMODE_RISING_EDGE,          // Rising Edge
        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
    };
 
    Timer_A_initContinuousModeParam continuousModeConfig = {
        TIMER_A_CLOCKSOURCE_SMCLK,          // SMCLK Clock Source
        TIMER_A_CLOCKSOURCE_DIVIDER_1,      // SMCLK = 16.384MHz
        TIMER_A_TAIE_INTERRUPT_DISABLE,     // Disable Overflow ISR
        TIMER_A_DO_CLEAR                    // Clear Counter
    };
 
 
    WDT_hold(WDT_BASE);
 
    // Setting the DCO to use the internal resistor. DCO will be at 16.384MHz
    // SMCLK = DCO = 16.384MHz
    // ACLK = 32kHz
    CS_setupDCO(CS_INTERNAL_RESISTOR);
    CS_initClockSignal(CS_SMCLK, CS_CLOCK_DIVIDER_1);
 
    // Set P1.2 to output ACLK
    GPIO_setAsPeripheralModuleFunctionOutputPin(GPIO_PORT_P1,
                                                GPIO_PIN2,
                                                GPIO_SECONDARY_MODULE_FUNCTION);
 
    // Set P1.5 to perform period measurement as CC1A
    GPIO_setAsPeripheralModuleFunctionInputPin(GPIO_PORT_P1,
                                               GPIO_PIN5,
                                               GPIO_SECONDARY_MODULE_FUNCTION);
 
 
    // Configure the timer to capture on rising edge of CC1A (P1.5)
    Timer_A_initCaptureMode(TIMER_A0_BASE, &captureModeConfig);
 
    // Configure the sampling timer
    Timer_A_initContinuousMode(TIMER_A0_BASE, &continuousModeConfig);
    Timer_A_startCounter(TIMER_A0_BASE, TIMER_A_CONTINUOUS_MODE);
 
    // Go into LPM0 with interrupts enabled. Don't exit until samples are done
    __bis_SR_register(LPM0_bits | GIE);
 
    // All samples recorded, blink LED to indicate done
    GPIO_setAsOutputPin(GPIO_PORT_P1, GPIO_PIN4);
 
    // Slow down clock so we can see LED blink
    // Configure MCLK = ~1MHz
    CS_initClockSignal(CS_MCLK, CS_CLOCK_DIVIDER_16);
 
    while(1) {
        // Toggle the LED state
        GPIO_toggleOutputOnPin(GPIO_PORT_P1, GPIO_PIN4);
        __delay_cycles(100000);
    }
}
 
#if defined(__TI_COMPILER_VERSION__) || defined(__IAR_SYSTEMS_ICC__)
#pragma vector=TIMER0_A1_VECTOR
__interrupt
#elif defined(__GNUC__)
__attribute__((interrupt(TIMER0_A1_VECTOR)))
#endif
void TA0_ISR(void) {
    switch(__even_in_range(TAIV, TA0IV_TAIFG)) {
        case TA0IV_NONE: break;
        case TA0IV_TACCR1:
            CaptureData[CaptureDataIndex++] = Timer_A_getCaptureCompareCount(TIMER_A0_BASE,
                                                                             TIMER_A_CAPTURECOMPARE_REGISTER_1);
            if(CaptureDataIndex == NUMBER_OF_CAPTURES) {
                // Enough samples, can disable interrupt
                Timer_A_disableCaptureCompareInterrupt(TIMER_A0_BASE, TIMER_A_CAPTURECOMPARE_REGISTER_1);
 
                // Exit from LPM0 and disable interrupts
                __bic_SR_register_on_exit(LPM0_bits | GIE);
            }
            break;
        case TA0IV_TACCR2: break;
        case TA0IV_TAIFG: break;
        default:   break;
    }
}