EK-TM4C1294XL: Trouble reading pulse width (continued)

Hi,

So I have already received help from Bob Crosby. Up until bob had helped me I was unable to get any constant reading for a known PWM. Now I do get a constant reading for PWMs with known pulse lengths but I have an irregularity - I thought to convert my pulse length into time I would have to divide by (120*10^6) to get my answer in seconds. This isn't the case, I have to use another constant to get my answer in seconds. It is a good amount off 120*10^6 - closer to 2 million.

If I use that constant I can get an accurate (within error range) pulse length reading when comparing it to oscilloscope (this includes PWMs with different pulse lengths) but I was wondering what could be causing my issue and if there is a possibility of this issue becoming a big problem in the future.

Here is my code relevant to the pulse width (I only want to read the pulse once at the moment):

#include <stdint.h>
#include <stdbool.h>
#include <math.h>
#include "inc/hw_ints.h"
#include "inc/hw_memmap.h"
#include "inc/hw_types.h"
#include "inc/hw_gpio.h"
#include "inc/hw_pwm.h"
#include "driverlib/debug.h"
#include "driverlib/fpu.h"
#include "driverlib/gpio.h"
#include "driverlib/pwm.h"
#include "driverlib/interrupt.h"
#include "driverlib/pin_map.h"
#include "driverlib/rom.h"
#include "driverlib/rom_map.h"
#include "driverlib/sysctl.h"
#include "driverlib/timer.h"
#include "driverlib/uart.h"
#include "utils/uartstdio.h"
#include <string.h>
#include <stdio.h>
#include "driverlib/sysctl.h"

// Global variable declaration for clock
uint32_t g_ui32SysClock;

// Global variable for Pulse
uint32_t  start = 0, end = 0, length = 0;

void Pulse_Length (void)
{
    //
    // Enable GPIO and Timer 0
    //
    SysCtlPeripheralEnable(SYSCTL_PERIPH_GPIOD);
    SysCtlPeripheralEnable(SYSCTL_PERIPH_TIMER0);

    //
    //Configure GPIO Timer Pins in
    //
    GPIOPinConfigure(GPIO_PD0_T0CCP0);
    GPIOPinConfigure(GPIO_PD1_T0CCP1);
    GPIOPinTypeTimer(GPIO_PORTD_BASE, GPIO_PIN_0 | GPIO_PIN_1);

    //
    // Initialize timer A and B to count up in edge time mode
    //
    TimerConfigure(TIMER0_BASE, (TIMER_CFG_SPLIT_PAIR | TIMER_CFG_A_CAP_TIME_UP | TIMER_CFG_B_CAP_TIME_UP));
    TimerClockSourceSet(TIMER0_BASE, TIMER_CLOCK_SYSTEM);
    //
    //Timer Load Value
    //
    TimerLoadSet(TIMER0_BASE, TIMER_BOTH, 0xFFFFu);

    //
    // Timer A records positive edge time and Timer B records negative edge time
    //
    TimerControlEvent(TIMER0_BASE, TIMER_A, TIMER_EVENT_POS_EDGE);
    TimerControlEvent(TIMER0_BASE, TIMER_B, TIMER_EVENT_NEG_EDGE);



    // Registers a interrupt function to be called when timer as hits positive edge trig int
    IntRegister(INT_TIMER0A, RisingEdge);
    // Set interrupt to the highest priority
    IntPrioritySet(INT_TIMER0A, 0);
    // Makes sure the interrupt is cleared
    TimerIntClear(TIMER0_BASE, TIMER_CAPA_EVENT);
    // Enable the indicated timer interrupt source.
    TimerIntEnable(TIMER0_BASE, TIMER_CAPA_EVENT);
    // The specified interrupt is enabled in the interrupt controller.
    IntEnable(INT_TIMER0A);

    // Registers a interrupt function to be called when timer as hits neg edge trig int
    IntRegister(INT_TIMER0B, FallingEdge);
    // Set interrupt to the highest priority
    IntPrioritySet(INT_TIMER0B, 0);
    // Makes sure the interrupt is cleared
    TimerIntClear(TIMER0_BASE, TIMER_CAPB_EVENT);
    // Enable the indicated timer interrupt source.
    TimerIntEnable(TIMER0_BASE, TIMER_CAPB_EVENT);
    // The specified interrupt is enabled in the interrupt controller.
    //IntEnable(INT_TIMER0B);

    TimerEnable(TIMER0_BASE, TIMER_BOTH); // needs to come after timer is configured
}

void RisingEdge (void)
{
//    if (PULSE_START == PulseState)
//    {
        TimerIntClear(TIMER0_BASE, TIMER_CAPA_EVENT);
        start = TimerValueGet(TIMER0_BASE, TIMER_A);
//        PulseState = PULSE_POS;
        IntDisable(INT_TIMER0A);
        IntEnable(INT_TIMER0B);
//    }
}

void FallingEdge (void)
{
//    if (PULSE_POS == PulseState)
//    {
        TimerIntClear(TIMER0_BASE, TIMER_CAPB_EVENT);
        end = TimerValueGet(TIMER0_BASE, TIMER_B);
        if(end < start)
        {
            end = end + 0x10000;
        }
        length = end - start;
//        PulseState=PULSE_NEG;
//    }
        //IntEnable(INT_TIMER0A); // This is disabled for acctual pulse
        IntDisable(INT_TIMER0B);
}

int
main(void)
{
    g_ui32SysClock = MAP_SysCtlClockFreqSet((SYSCTL_XTAL_25MHZ |
                                                 SYSCTL_OSC_MAIN |
                                                 SYSCTL_USE_PLL |
                                                 SYSCTL_CFG_VCO_480), 120000000);

    FPUEnable();
    FPURoundingModeSet(FPU_ROUND_POS_INF);    
    Pulse_Length();

    IntMasterEnable();
    while(1)
        {
            SysCtlDelay(40000000);
            UARTprintf("Length = %d\n", length);
        }
}