/* p5_10.c using Timer_A0.2 for capture mode of pin P2.5.
 *
 * This program uses TA0.2 for capture mode of pin P2.5.
 * SMCLK is running at 3 MHz. Timer_A0 is free-running
 * without input clock dividers. When rising edge of P2.5
 * occurs, the content of TA0R is copied into TIMER_A0->CCR[2] and
 * CCIFG flag in TIMER_A0->CCTL[2] is set.
 * Two timestamps are taken and the difference is the
 * period of the input signal. By shifting the difference
 * 13 bits to the right, it is displayed on the tri-color LEDs.
 * It works well up to about 150 Hz with 13-bit shift.
 * To run this program, you need to connect a 0-3V periodic
 * signal to pin P2.5.
 *
 * Tested with Keil 5.20 and MSP432 Device Family Pack V2.2.0
 * on XMS432P401R Rev C.
 */
#include "msp.h"

int main(void) {
    unsigned short last, current, diff;

    /* initialize P2.2-P2.0 for tri-color LEDs */
    P2->SEL1 &= ~7;         /* configure P2.2-P2.0 as simple I/O */
    P2->SEL0 &= ~7;
    P2->DIR  |= 7;          /* P2.2-P2.0 set as output */

    /* configure P2.5 as TA0.CCI1A */
    P2->SEL1 &= ~0x20;
    P2->SEL0 |= 0x20;
    P2->DIR  &= ~0x20;

    TIMER_A0->CTL = 0x0224;     /* SMCLK, ID = /1, up mode, TA clear */
    TIMER_A0->CCTL[2] = 0x4900; /* rising edge, CCI2A, SCS, capture mode */
    TIMER_A0->EX0 = 0;          /* IDEX = /1 */

    while (1) {
        TIMER_A0->CCTL[2] &= ~1;             /* clear interrupt flag */
        while((TIMER_A0->CCTL[2] & 1) == 0); /* wait until the CCIFG is set */
        last = TIMER_A0->CCR[2];             /* save first timestamp */

        TIMER_A0->CCTL[2] &= ~1;             /* clear interrupt flag */
        while((TIMER_A0->CCTL[2] & 1) == 0); /* wait until the CCIFG is set */
        current = TIMER_A0->CCR[2];          /* save second timestamp */

        diff = current - last;      /* display the time interval */
        P2->OUT = diff >> 13;
    }
}