/* Generate control signal for a standard servo motor.
 *
 * Using Timer_A0.4 PWM to generate a 50 Hz signal at P2.7
 * with pulse width varies between 1 ms and 2 ms. This should
 * control the servo motor to turn clockwise and counterclockwise.
 * This program controls J5 PWM1 output of the EduPad board.
 *
 * Built and tested with MSP432P401R Rev. C, Keil MDK-ARM v5.24a and MSP432P4xx_DFP v3.1.0
 */

#include "msp.h"

void delayMs(int n);

int main(void) {
    int pw;
    
	/* Configure P2.7 as Timer A0.4 output */
    P2->SEL0 |= 0x80;
    P2->SEL1 &= ~0x80;
    P2->DIR |= 0x80;

    /* configure TimerA0.4 as PWM */
    TIMER_A0->CCR[0] = 60000 - 1;   /* PWM Period */
    TIMER_A0->CCR[4] = 3000 - 1;    /* CCR4 PWM duty cycle */
    TIMER_A0->CCTL[4] = 0xE0;       /* CCR4 reset/set mode */
    TIMER_A0->CTL = 0x0214;         /* use SMCLK, count up, clear TA0R register */

    while(1) {
        // ramp up the pulse width
        for (pw = 3000 - 1; pw < 6000 - 1; pw += 50) {
            TIMER_A0->CCR[4] = pw;
            delayMs(20);
        }
        
        // ramp down the pulse width
        for (pw = 6000 - 1; pw > 3000 - 1; pw -= 50) {
            TIMER_A0->CCR[4] = pw;
            delayMs(20);
        }
    }
}

/* system clock at 3 MHz, MSP432P401R Rev. C, Start-up v2.2.1 */
void delayMs(int n) {
    int i, j;
    
    for (j = 0; j < n; j++)
        for (i = 750; i > 0; i--);      /* Delay */
}