/* Generate control signal for a standard servo motor.
 *
 * The PWM1 Generator 3B is used to generate a 50 Hz signal
 * with pulse width varies between 1 ms and 2 ms. This should
 * control the servo motor to turn clockwise and counterclockwise.
 * The EduPad board has four servo motor control
 * pins PF0, PF1, PF2, and PF3. This program controls PF3.
 * The signal is on J5 header PWM2.
 *
 * Built and tested with Keil MDK-ARM v5.24a and TM4C_DFP v1.1.0
 */

#include "TM4C123GH6PM.h"

void delayMs(int n);

int main(void) {
    int pw = 0;
   
    SYSCTL->RCGCPWM |= 0x02;        // enable clock to PWM1
    SYSCTL->RCGCGPIO |= 0x20;       // enable clock to GPIOF

    SYSCTL->RCC |=  0x00100000;     // enable clock divider for PWM
    SYSCTL->RCC &= ~0x000E0000;     // clear clock divide
    SYSCTL->RCC |=  0x00060000;     // set clock divide to 16 (50 MHz / 16 = 3.125 MHz)
    
    delayMs(1);                     // wait for PWM clock to stablize
    PWM1->INVERT |= 0x80;           // positive pulse
    PWM1->_3_CTL = 0;               // disable PWM1_3 during configuration
    PWM1->_3_GENB = 0x0000080C;     // output high when load and low when match
    PWM1->_3_LOAD = 62500 - 1;      // 50 Hz 
    PWM1->_3_CMPB = 3125 - 1;       // 1000 us
    PWM1->_3_CTL = 1;               // enable PWM1_3
    PWM1->ENABLE |= 0x80;           // enable PWM1

    GPIOF->DIR |= 0x08;             // set PORTF 3 pins as output pin
    GPIOF->DEN |= 0x08;             // set PORTF 3 pins as digital pins
    GPIOF->AFSEL |= 0x08;           // enable alternate function
    GPIOF->PCTL &= ~0x0000F000;     // clear PORTF 3 alternate function
    GPIOF->PCTL |= 0x00005000;      // set PORTF 3 alternate funtion to PWM

    while(1) {
        // ramp up the pulse width
        for (pw = 3124; pw < 6249; pw += 50) {
            PWM1->_3_CMPB = pw;
            delayMs(20);
        }
        
        // ramp down the pulse width
        for (pw = 6249; pw > 3124; pw -= 50) {
            PWM1->_3_CMPB = pw;
            delayMs(20);
        }
    }
}

/* delay n milliseconds (50 MHz CPU clock) */
void delayMs(int n) {
    int i, j;
    for(i = 0 ; i< n; i++)
        for(j = 0; j < 6265; j++)
            {}  /* do nothing for 1 ms */
}