/* p11_4: Use PWM to control LED duty cycle */

/* This program is based on p11_3. Some parameters are changed to slow down the PWM frequency so that it runs slow enough to observe the duty cycle change from the LED with naked eyes. */

#include "TM4C123GH6PM.h"

int main(void)
{
    void delayMs(int n);
    int x = 0xFFFE;
    
    /* Enable Peripheral Clocks */
    SYSCTL->RCGCPWM |= 2;       /* enable clock to PWM1 */
    SYSCTL->RCGCGPIO |= 0x20;   /* enable clock to PORTF */
    SYSCTL->RCC |= 0x00100000;  /* use pre-divide for PWM clock */
    SYSCTL->RCC |= 0x000E0000;  /* set 64 for pre-divide for PWM */ 

    /* Enable port PF3 for PWM1 M1PWM7 */
    
    GPIOF->AFSEL = 8;           /* PF3 uses alternate function */
    GPIOF->PCTL &= ~0x0000F000; /* make PF3 PWM output pin */
    GPIOF->PCTL |= 0x00005000;
    GPIOF->DEN |= 8;            /* pin digital */
    
    PWM1->_3_CTL = 0;           /* stop counter */
    PWM1->_3_GENB = 0x0000008C; /* M1PWM7 output set when reload, */
                                /* clear when match PWMCMPA */
    PWM1->_3_LOAD = 0xFFFF;     /* set load value with max value */
    PWM1->_3_CMPA = x;          /* set duty cycle to 50% */
    PWM1->_3_CTL = 1;           /* start timer */
    PWM1->ENABLE = 0x80;        /* start PWM1 ch7 */
    
    for(;;) 
    {
        x = x - 1000;
        if (x <= 0) x = 0xFFFE;
        PWM1->_3_CMPA = x;
        delayMs(300);
    }
}

/* delay n milliseconds (16 MHz CPU clock) */
void delayMs(int n)
{
    int i, j;
    for(i = 0 ; i < n; i++)
        for(j = 0; j < 3180; j++)
            {}  /* do nothing for 1 ms */
}

/* This function is called by the startup assembly code to perform system specific initialization tasks. */
void SystemInit(void)
{
    /* Grant coprocessor access */
    /* This is required since TM4C123G has a floating point coprocessor */
    SCB->CPACR |= 0x00f00000;
}