EK-TM4C123GXL: RTC

Hi Ralph, 

Thanks, and yes I should have been more clear about what I need. There are things I need:

1) A 1 microsecond interrupt to trigger my scheduler.

2) A place and efficient method to keep a count of microseconds since power up. I thought about using a pair of timers in RTC mode but Section 11.3.2.2 states: The input clock on a CCP0 input is required to be 32.768 KHz in RTC mode. The clock signal is then divided down to a 1-Hz rate and is passed along to the input of the counter. I need microsecond resolution so I have continued with the systick route. The code below works but I am trying to determine if there is a better way using the non-ARM timers or maybe a combination of SysTick and a timer.

#include <stdbool.h>
#include <stdint.h>
#include <driverlib/systick.h>
#include <driverlib/sysctl.h>
#include "driverlib/gpio.h"
#include "driverlib/rom_map.h"
#include "inc/hw_memmap.h"


#define LEDS (GPIO_PIN_1 | GPIO_PIN_2 |GPIO_PIN_3)
#define SYSTEM_TICKS_PER_SECOND 1000000UL

static uint64_t ticks;

static void timeISR();
uint64_t    getTicks();



static void
timeISR()
{
    ticks++;
    GPIOPinWrite(GPIO_PORTF_BASE, LEDS, GPIO_PIN_2); //Blue
    GPIOPinWrite(GPIO_PORTF_BASE, LEDS, 0);
}


uint64_t
getTicks()
{
    volatile uint64_t pete;
    volatile uint64_t repeat;
    int i = 0;
    volatile static int max = 0;

    //Deal with ISR updates during non-atomic read
    pete   = ticks;
    repeat = ticks;

    while ( pete != repeat )
    {
      pete   = repeat;
      repeat = ticks;
      i++;
    }
    if (i > max)
        max = i;
    return pete;
}


int
main(void)
{
    volatile uint64_t t = 0;

    MAP_SysCtlClockSet(SYSCTL_SYSDIV_2_5 | SYSCTL_USE_PLL | SYSCTL_OSC_MAIN | SYSCTL_XTAL_16MHZ);

    SysCtlPeripheralEnable(SYSCTL_PERIPH_GPIOF);
    GPIOPinTypeGPIOOutput(GPIO_PORTF_BASE, LEDS);

    SysTickPeriodSet(SysCtlClockGet() / SYSTEM_TICKS_PER_SECOND);
    SysTickIntRegister(timeISR);
    SysTickEnable();
    SysTickIntEnable();

    while (1)
    {
       t = getTicks();
    }
}