LM4F120 LUNCHPAD的串口问题。

//*****************************************************************************
//
// gpio_jtag.c - Example to demonstrate recovering the JTAG interface.
//
// Copyright (c) 2012 Texas Instruments Incorporated.  All rights reserved.
// Software License Agreement
// 
// Texas Instruments (TI) is supplying this software for use solely and
// exclusively on TI's microcontroller products. The software is owned by
// TI and/or its suppliers, and is protected under applicable copyright
// laws. You may not combine this software with "viral" open-source
// software in order to form a larger program.
// 
// THIS SOFTWARE IS PROVIDED "AS IS" AND WITH ALL FAULTS.
// NO WARRANTIES, WHETHER EXPRESS, IMPLIED OR STATUTORY, INCLUDING, BUT
// NOT LIMITED TO, IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
// A PARTICULAR PURPOSE APPLY TO THIS SOFTWARE. TI SHALL NOT, UNDER ANY
// CIRCUMSTANCES, BE LIABLE FOR SPECIAL, INCIDENTAL, OR CONSEQUENTIAL
// DAMAGES, FOR ANY REASON WHATSOEVER.
// 
// This is part of revision 9453 of the EK-LM4F120XL Firmware Package.
//
//*****************************************************************************

#include "inc/hw_gpio.h"
#include "inc/hw_ints.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/interrupt.h"
#include "driverlib/pin_map.h"
#include "driverlib/rom.h"
#include "driverlib/sysctl.h"
#include "driverlib/systick.h"
#include "utils/uartstdio.h"
#include "drivers/buttons.h"

//*****************************************************************************
//
//! \addtogroup example_list
//! <h1>GPIO JTAG Recovery (gpio_jtag)</h1>
//!
//! This example demonstrates changing the JTAG pins into GPIOs, along with a
//! mechanism to revert them to JTAG pins.  When first run, the pins remain in
//! JTAG mode.  Pressing the left button will toggle the pins between JTAG mode
//! and GPIO mode.  Because there is no debouncing of the push button (either
//! in hardware or software), a button press will occasionally result in more
//! than one mode change.
//!
//! In this example, four pins (PC0, PC1, PC2, and PC3) are switched.
//!
//! UART0, connected to the ICDI virtual COM port and running at 115,200,
//! 8-N-1, is used to display messages from this application.
//
//*****************************************************************************


//*****************************************************************************
//
// The current mode of pins PC0, PC1, PC2, and PC3.  When zero, the pins
// are in JTAG mode; when non-zero, the pins are in GPIO mode.
//
//*****************************************************************************
volatile unsigned long g_ulMode;

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

//*****************************************************************************
//
// The interrupt handler for the PB4 pin interrupt.  When triggered, this will
// toggle the JTAG pins between JTAG and GPIO mode.
//
//*****************************************************************************
void
SysTickIntHandler(void)
{
    unsigned char ucButtons;
    unsigned char ucButtonsChanged;

    //
    // Grab the current, debounced state of the buttons.
    //
    ucButtons = ButtonsPoll(&ucButtonsChanged, 0);

    //
    // If the left button has been pressed, and was previously not pressed,
    // start the process of changing the behavior of the JTAG pins.
    //
    if(BUTTON_PRESSED(LEFT_BUTTON, ucButtons, ucButtonsChanged))
    {
        //
        // Toggle the pin mode.
        //
        g_ulMode ^= 1;

        //
        // See if the pins should be in JTAG or GPIO mode.
        //
        if(g_ulMode == 0)
        {
           
        }
        else
        {
           
        }
    }
}

//*****************************************************************************
//
// Toggle the JTAG pins between JTAG and GPIO mode with a push button selecting
// between the two.
//
//*****************************************************************************
int
main(void)
{
    unsigned long ulMode;

    //
    // 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.
    //
    ROM_SysCtlClockSet(SYSCTL_SYSDIV_4 | SYSCTL_USE_PLL | SYSCTL_XTAL_16MHZ |
                       SYSCTL_OSC_MAIN);

    //
    // Enable the peripherals used by this application.
    //
    ROM_SysCtlPeripheralEnable(SYSCTL_PERIPH_GPIOA);
    ROM_SysCtlPeripheralEnable(SYSCTL_PERIPH_GPIOC);
	  ROM_SysCtlPeripheralEnable(SYSCTL_PERIPH_GPIOD);
    SysCtlPeripheralEnable(SYSCTL_PERIPH_UART2);
    //
    // Initialize the button driver.
    //
    ButtonsInit();

    //
    // Set up a SysTick Interrupt to handle polling and debouncing for our
    // buttons.
    //
    SysTickPeriodSet(SysCtlClockGet() / 100);
    SysTickIntEnable();
    SysTickEnable();
    IntMasterEnable();
    g_ulMode = 0;
    ulMode = 0;
    //
    // Configure GPIO.
    //
    //ROM_GPIOPinTypeGPIOOutput(GPIO_PORTF_BASE, GPIO_PIN_3 | GPIO_PIN_1);
    //ROM_GPIOPinWrite(GPIO_PORTF_BASE, GPIO_PIN_3 | GPIO_PIN_1, GPIO_PIN_3);

    //
    // Set the global and local indicator of pin mode to zero, meaning JTAG.
    //


    //
    // Initialize the UART.
    //
    GPIOPinConfigure(GPIO_PD6_U2RX);
    GPIOPinConfigure(GPIO_PD7_U2TX);
    ROM_GPIOPinTypeUART(GPIO_PORTD_BASE, GPIO_PIN_6 | GPIO_PIN_7);
    UARTStdioInit(2);




    //
    // Loop forever.  This loop simply exists to display on the UART the
    // current state of PC0-3; the handling of changing the JTAG pins to and
    // from GPIO mode is done in GPIO Interrupt Handler.
    //
    while(1)
    {

      UARTCharPut(UART2_BASE, 0);
      //UARTprintf("1");
    }
}