/* www.MicroDigitalEd.com
 * p6_7.c Waveform generation using Timer_A0.4 compare
 *
 * This program uses TA0.4 in compare mode to generate
 * periodic signal on pin P2.7.
 * System clock is running at 3 MHz. Clock input dividers are
 * set to divide by 8 and 8. TA0 is set to continuous mode. 
 * TA0.4 is configured for compare mode. When the 
 * TA0R counter value matches TIMER_A0->CCR[4], the output is set to toggle.
 * It also triggers an interrupt. In the interrupt handler, 
 * 11719 is added to TIMER_A0->CCR[4] so that the next toggle occurs
 * 11719 cycles (250 ms) later. Both P2.7 and P2.1 toggle at 250 ms period.
 *
 * Since none of the LEDs is connected to a Timer_A output, 
 * Port Map is used to connect the TA0.4 output to P2.1, which
 * is connected to the green LED.
 *
 * Tested with Keil 5.20 and MSP432 Device Family Pack V2.2.0.
 */

#include "msp.h"

int main(void) {
    void redirect(void);

    __disable_irq();

    /* set up TA0.4 to do compare */
    TIMER_A0->CTL = 0x02E4;     /* SMCLK, ID = /8, continuous mode, TA clear */
    TIMER_A0->EX0 = 7;          /* IDEX = /8 */
    TIMER_A0->CCTL[4] = 0x80;   /* OUTMOD = toggle */
    TIMER_A0->CCR[4] = 11719;   /* toggle point */
    TIMER_A0->CCTL[4] |= 0x10;  /* enable CC interrupt */

    /* Configure P2.7 as Timer A0.4 compare output */
    P2->SEL0 |= 0x80;
    P2->SEL1 &= ~0x80;
    P2->DIR |= 0x80;

    redirect();         /* connect TA0.4 output to pin P2.1 */

    NVIC_SetPriority(TA0_N_IRQn, 3);    /* set priority to 3 in NVIC */
    NVIC_EnableIRQ(TA0_N_IRQn);         /* enable interrupt in NVIC */
    __enable_irq();                     /* global enable IRQs */   
    
    while (1) {
    }
}

void TA0_N_IRQHandler(void) {
    TIMER_A0->CCTL[4] &= ~1;         /* clear interrupt flag */
    TIMER_A0->CCR[4] += 11719;       /* schedule next toggle */
}

/* This function connects the output of TA0.4 to pin P2.1 */
void redirect(void) {
    PMAP->KEYID = 0x2D52;     /* unlock PMAP */
    P2MAP->PMAP_REGISTER1 = PMAP_TA0CCR4A;  /* 23, map P2.1 to TA0.4 */
    P2->DIR |= 2;             /* set up P2.1 to take TA0.4 output */
    P2->SEL0 |= 2;
    P2->SEL1 &= ~2;
    PMAP->CTL = 1;            /* lock PMAP */
    PMAP->KEYID = 0;
}