/* www.microDigitalEd.com
 * p5_9.c Toggling green LEDs at 1 Hz using Timer_A and Auxiliary clock
 *
 * This program uses Timer_A to generate 1 second delay to
 * toggle the green LED.
 * Auxiliary clock (ACLK) running at 32,768 Hz is used. 
 * Timer_A is configured to count up from 0 to 512-1, 
 * which is loaded in TIMER_A1->CCR[0].
 * When the counter (TA1R) value reaches TIMER_A1->CCR[0], 
 * the CCIFG bit in TIMER_A1->CCTL[0] is set.
 * The clock input dividers are set to divide by 8 and 8 again.
 * The timer counter roll over interval is:
 * 32,768 / 8 / 8 / 512 = 1 Hz.
 * The green LED is connected to P2.1.
 *
 * Tested with Keil 5.20 and MSP432 Device Family Pack V2.2.0.
 */

#include "msp.h"

int main(void) {
    /* initialize P2.1 for green LED */
    P2->SEL1 &= ~2;         /* configure P2.1 as simple I/O */
    P2->SEL0 &= ~2;
    P2->DIR |= 2;           /* P2.1 set as output */

    TIMER_A1->CTL = 0x01D1;     /* ACLK, ID = /8, up mode, TA clear */ 
    TIMER_A1->CCR[0] = 512 - 1; /* for 1 sec */
    TIMER_A1->EX0 = 7;          /* IDEX = /8 */

    while (1) {
        while((TIMER_A1->CCTL[0] & 1) == 0); /* wait until the CCIFG flag is set */
        TIMER_A1->CCTL[0] &= ~1;            /* clear interrupt flag */
        P2->OUT ^= 2;                       /* toggle green LED */
    }
}