TM4C123GH6ZRB Cannot get into Stellaris Bootloader after first time programming

Hello All,

I am working on a prototype board which uses the TM4C123GH6ZRB micro-controller.  I am programming this board through USB interface while running the controller in the ROM bootloader mode (pre-loaded TI bootloader).

The first time I powered up the board, I put the micro-controller in the ROM bootloader mode by setting PB7 low.  When I connected my PC to the TM4C123G through USB for the first time, my PC detects the Stellaris device and I can program the chip using the LMFlashProgrammer software.

The problem I am facing is after the first successful program, I can no longer get into the ROM bootloader by setting PB7 low.  When I put PB7 pin low and connect my PC to the device through USB, my PC does not detect the stellaris device and I cannot see the device through LMFlashProgrammer.  When using the LMFlash programmer can the "Program Address Offset" cause this type of problem?

Below is the code I am loading into the device based off of the EKTM4C123GXL launch pad Evaluation Kit.  I am not reconfiguring my bootcfg register to alter default ROM bootloading pin.  The external oscillator speed is 12Mhz instead of the 16Mhz used on the evaluation board.

I have PART=TM4C123GH6ZRB defined in the makefile.  Thanks for the help!

#include <stdint.h>
#include <stdbool.h>
#include "inc/hw_memmap.h"
#include "inc/hw_types.h"
#include "driverlib/debug.h"
#include "driverlib/fpu.h"
#include "driverlib/gpio.h"
#include "driverlib/pin_map.h"
#include "driverlib/rom.h"
#include "driverlib/sysctl.h"
#include "driverlib/uart.h"
#include "utils/uartstdio.h"

//*****************************************************************************
//
//! \addtogroup example_list
//! <h1>Hello World (hello)</h1>
//!
//! A very simple ``hello world'' example.  It simply displays ``Hello World!''
//! on the UART and is a starting point for more complicated applications.
//!
//! UART0, connected to the Virtual Serial Port and running at
//! 115,200, 8-N-1, is used to display messages from this application.
//
//*****************************************************************************

//*****************************************************************************
//
// The error routine that is called if the driver library encounters an error.
//
//*****************************************************************************
#ifdef DEBUG
void
__error__(char *pcFilename, uint32_t ui32Line)
{
}
#endif

//*****************************************************************************
//
// Configure the UART and its pins.  This must be called before UARTprintf().
//
//*****************************************************************************
void
ConfigureUART(void)
{
    //
    // Enable the GPIO Peripheral used by the UART.
    //
    ROM_SysCtlPeripheralEnable(SYSCTL_PERIPH_GPIOA);

    //
    // Enable UART0
    //
    ROM_SysCtlPeripheralEnable(SYSCTL_PERIPH_UART0);

    //
    // Configure GPIO Pins for UART mode.
    //
    ROM_GPIOPinConfigure(GPIO_PA0_U0RX);
    ROM_GPIOPinConfigure(GPIO_PA1_U0TX);
    ROM_GPIOPinTypeUART(GPIO_PORTA_BASE, GPIO_PIN_0 | GPIO_PIN_1);

    //
    // Use the internal 16MHz oscillator as the UART clock source.
    //
    UARTClockSourceSet(UART0_BASE, UART_CLOCK_PIOSC);

    //
    // Initialize the UART for console I/O.
    //
    UARTStdioConfig(0, 115200, 16000000);
}

//*****************************************************************************
//
// Print "Hello World!" to the UART on the evaluation board.
//
//*****************************************************************************
int
main(void)
{
    //volatile uint32_t ui32Loop;

    //
    // Enable lazy stacking for interrupt handlers.  This allows floating-point
    // instructions to be used within interrupt handlers, but at the expense of
    // extra stack usage.
    //
    ROM_FPULazyStackingEnable();

    //
    // Set the clocking to run directly from the crystal.
    //
    // Commented out 16Mhz because this is used for evaluation board and not RGBT
    //ROM_SysCtlClockSet(SYSCTL_SYSDIV_4 | SYSCTL_USE_PLL | SYSCTL_XTAL_16MHZ |
    //                   SYSCTL_OSC_MAIN);

    ROM_SysCtlClockSet(SYSCTL_SYSDIV_4 | SYSCTL_USE_PLL | SYSCTL_XTAL_12MHZ |
                       SYSCTL_OSC_MAIN);

    //
    // Enable the GPIO port that is used for the on-board LED.
    //
    ROM_SysCtlPeripheralEnable(SYSCTL_PERIPH_GPIOF);

    //
    // Enable the GPIO pins for the LED (PF2 & PF3).
    //
    ROM_GPIOPinTypeGPIOOutput(GPIO_PORTF_BASE, GPIO_PIN_2);

    //
    // Initialize the UART.
    //
    ConfigureUART();

    //
    // Hello!
    //
    UARTprintf("Hello, world!\n");

    //
    // We are finished.  Hang around doing nothing.
    //
    while(1)
    {
		UARTprintf("Hello, world!\n");
        //
        // Turn on the BLUE LED.
        //
        GPIOPinWrite(GPIO_PORTF_BASE, GPIO_PIN_2, GPIO_PIN_2);

        //
        // Delay for a bit.
        //
        SysCtlDelay(SysCtlClockGet() / 10 / 3);

        //
        // Turn off the BLUE LED.
        //
        GPIOPinWrite(GPIO_PORTF_BASE, GPIO_PIN_2, 0);

        //
        // Delay for a bit.
        //
        SysCtlDelay(SysCtlClockGet() / 10 / 3);
    }
}