#include <stdint.h>
#include "tm4c123gh6pm.h"

#define STCTRL *((volatile uint32_t *) 0xE000E010)        // Control and status
#define STRELOAD *((volatile uint32_t *) 0xE000E014)      // Reload value
#define STCURRENT *((volatile uint32_t *) 0xE000E018)     // Current value

#define ENABLE (1 << 0)      // Bit 0 of CSR to enable the timer
#define CLKINT (1 << 2)      // Bit 2 of CSR to specify CPU clock
#define CLOCK_HZ 16000000    // Clock frequency of EK-TM4C123GXL
#define SYSTICK_RELOAD_VALUE(us) ((CLOCK_HZ / 1000000) * (us) - 1)   // SysTick reload value in microseconds based on clock frequency

void systick_setting(void) 
{
    STRELOAD = SYSTICK_RELOAD_VALUE(1000);     // RELOAD VALUE FOR 1ms
    STCTRL |= ENABLE | CLKINT;                 // Enable SysTick with system clock
    STCURRENT = 0;                             // Clear current value
}

void delay(int us) 
{
    STRELOAD = SYSTICK_RELOAD_VALUE(us);        // RELOAD VALUE FOR REQUIRED DELAY
    STCURRENT = 0;                              // Clear STCURRENT
    STCTRL |= ENABLE | CLKINT;                  // Enable SysTick
    while ((STCTRL & (1 << 16)) == 0);          // Wait until flag is set
    STCTRL &= ~ENABLE;                          // Stop the timer
}