/*  p5_3.c: Count up the LEDs using the SysTick Counter */

/* This program sets up the SysTick to set the COUNT flag at 2 Hz. The system clock is running at 16 MHz.
  0.5sec / 62.5ns = 8,000,000 for RELOAD register since 1 / 0.5sec = 2Hz
The program then polls the flag and counts up a software counter every time COUNT flag is set. The counter value is written to the tri-color LEDs.
  The COUNT flag (D16 of CTRL reg.)is cleared when the STCTRL register is read. */


#include "TM4C123GH6PM.h"

int main (void)
{
    int myCount  = 0;
    
    /* enable clock to GPIOF at clock gating control register */
    SYSCTL->RCGCGPIO |= 0x20;
    /* enable the GPIO pins for the LED (PF3, PF2, and PF1) as output */
    GPIOF->DIR = 0x0E;
    /* enable the GPIO pins for digital function */
    GPIOF->DEN = 0x0E;
    
    /* Configure SysTick */
    SysTick->LOAD = 8000000-1;   /* reload with number of clocks per half second */
    SysTick->CTRL = 5;    /* enable it, no interrupt, use system clock */

    while (1)
    {
        if (SysTick->CTRL & 0x10000)   /* if COUNT flag (D16 of CTRL reg.) is set */
        {
            myCount++;
            GPIOF->DATA = myCount;    /* write the count to LEDs */
        }
    }
}

/* This function is called by the startup assembly code to perform system specific initialization tasks. */
void SystemInit(void)
{
    __disable_irq();    /* disable all IRQs */
    
    /* Grant coprocessor access */
    /* This is required since TM4C123G has a floating point coprocessor */
    SCB->CPACR |= 0x00F00000;
}