说明你代码使将JTAG锁定了，当然每次下载都需要重新解锁才能用，不然无法保障知识产权。
M4部分IO默认是锁定的，如果你需要使用，需要先解锁才能配置使用，在数据手册的GPIO那章节有详细说明。
GPIO和JTAG转换参考下面的代码例程：
//*****************************************************************************
//
// gpio_jtag.c - Example to demonstrate recovering the JTAG interface.
//
// Copyright (c) 2012-2015 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 2.1.1.71 of the EK-TM4C123GXL Firmware Package.
//
//*****************************************************************************
#include
#include
#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 "driverlib/uart.h"
#include "utils/uartstdio.h"
#include "drivers/buttons.h"
//*****************************************************************************
//
//! addtogroup example_list
//!

GPIO JTAG Recovery (gpio_jtag)

//!
//! This example demonstrates changing the JTAG pins into GPIOs, aint32_t 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 uint32_t g_ui32Mode;
//*****************************************************************************
//
// The error routine that is called if the driver library encounters an error.
//
//*****************************************************************************
#ifdef DEBUG
void
__error__(char *pcFilename, uint32_t ui32Line)
[
]
#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)
[
uint8_t ui8Buttons;
uint8_t ui8ButtonsChanged;
//
// Grab the current, debounced state of the buttons.
//
ui8Buttons = ButtonsPoll(&ui8ButtonsChanged, 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, ui8Buttons, ui8ButtonsChanged))
[
//
// Toggle the pin mode.
//
g_ui32Mode ^= 1;
//
// See if the pins should be in JTAG or GPIO mode.
//
if(g_ui32Mode == 0)
[
//
// Change PC0-3 into hardware (i.e. JTAG) pins.
//
HWREG(GPIO_PORTC_BASE + GPIO_O_LOCK) = GPIO_LOCK_KEY;
HWREG(GPIO_PORTC_BASE + GPIO_O_CR) = 0x01;
HWREG(GPIO_PORTC_BASE + GPIO_O_AFSEL) |= 0x01;
HWREG(GPIO_PORTC_BASE + GPIO_O_LOCK) = GPIO_LOCK_KEY;
HWREG(GPIO_PORTC_BASE + GPIO_O_CR) = 0x02;
HWREG(GPIO_PORTC_BASE + GPIO_O_AFSEL) |= 0x02;
HWREG(GPIO_PORTC_BASE + GPIO_O_LOCK) = GPIO_LOCK_KEY;
HWREG(GPIO_PORTC_BASE + GPIO_O_CR) = 0x04;
HWREG(GPIO_PORTC_BASE + GPIO_O_AFSEL) |= 0x04;
HWREG(GPIO_PORTC_BASE + GPIO_O_LOCK) = GPIO_LOCK_KEY;
HWREG(GPIO_PORTC_BASE + GPIO_O_CR) = 0x08;
HWREG(GPIO_PORTC_BASE + GPIO_O_AFSEL) |= 0x08;
HWREG(GPIO_PORTC_BASE + GPIO_O_LOCK) = GPIO_LOCK_KEY;
HWREG(GPIO_PORTC_BASE + GPIO_O_CR) = 0x00;
HWREG(GPIO_PORTC_BASE + GPIO_O_LOCK) = 0;
//
// Turn on the LED to indicate that the pins are in JTAG mode.
//
ROM_GPIOPinWrite(GPIO_PORTF_BASE, GPIO_PIN_3 | GPIO_PIN_1,
GPIO_PIN_3);
]
else
[
//
// Change PC0-3 into GPIO inputs.
//
HWREG(GPIO_PORTC_BASE + GPIO_O_LOCK) = GPIO_LOCK_KEY;
HWREG(GPIO_PORTC_BASE + GPIO_O_CR) = 0x01;
HWREG(GPIO_PORTC_BASE + GPIO_O_AFSEL) &= 0xfe;
HWREG(GPIO_PORTC_BASE + GPIO_O_LOCK) = GPIO_LOCK_KEY;
HWREG(GPIO_PORTC_BASE + GPIO_O_CR) = 0x02;
HWREG(GPIO_PORTC_BASE + GPIO_O_AFSEL) &= 0xfd;
HWREG(GPIO_PORTC_BASE + GPIO_O_LOCK) = GPIO_LOCK_KEY;
HWREG(GPIO_PORTC_BASE + GPIO_O_CR) = 0x04;
HWREG(GPIO_PORTC_BASE + GPIO_O_AFSEL) &= 0xfb;
HWREG(GPIO_PORTC_BASE + GPIO_O_LOCK) = GPIO_LOCK_KEY;
HWREG(GPIO_PORTC_BASE + GPIO_O_CR) = 0x08;
HWREG(GPIO_PORTC_BASE + GPIO_O_AFSEL) &= 0xf7;
HWREG(GPIO_PORTC_BASE + GPIO_O_LOCK) = GPIO_LOCK_KEY;
HWREG(GPIO_PORTC_BASE + GPIO_O_CR) = 0x00;
HWREG(GPIO_PORTC_BASE + GPIO_O_LOCK) = 0;
ROM_GPIOPinTypeGPIOInput(GPIO_PORTC_BASE, (GPIO_PIN_0 | GPIO_PIN_1 |
GPIO_PIN_2 | GPIO_PIN_3));
//
// Turn off the LED to indicate that the pins are in GPIO mode.
//
ROM_GPIOPinWrite(GPIO_PORTF_BASE, GPIO_PIN_3 | GPIO_PIN_1,
GPIO_PIN_1);
]
]
]
//*****************************************************************************
//
// 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);
]
//*****************************************************************************
//
// Toggle the JTAG pins between JTAG and GPIO mode with a push button selecting
// between the two.
//
//*****************************************************************************
int
main(void)
[
uint32_t ui32Mode;
//
// 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);
//
// Initialize the button driver.
//
ButtonsInit();
//
// Set up a SysTick Interrupt to handle polling and debouncing for our
// buttons.
//
SysTickPeriodSet(SysCtlClockGet() / 100);
SysTickIntEnable();
SysTickEnable();
IntMasterEnable();
//
// Configure the LED as an output and turn it on.
//
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.
//
g_ui32Mode = 0;
ui32Mode = 0;
//
// Initialize the UART.
//
ConfigureUART();
UARTprintf("33[2JGPIO <-> JTAGn");
//
// Indicate that the pins start out as JTAG.
//
UARTprintf("Pins are JTAGn");
//
// 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)
[
//
// Wait until the pin mode changes.
//
while(g_ui32Mode == ui32Mode)
[
]
//
// Save the new mode locally so that a subsequent pin mode change can
// be detected.
//
ui32Mode = g_ui32Mode;
//
// See what the new pin mode was changed to.
//
if(ui32Mode == 0)
[
//
// Indicate that PC0-3 are currently JTAG pins.
//
UARTprintf("Pins are JTAGn");
]
else
[
//
// Indicate that PC0-3 are currently GPIO pins.
//
UARTprintf("Pins are GPIOn");
]
]
]

Maka：
您好，
谢谢您的回复。
我查询data sheet 时也注意到了这个锁定问题，但是并没有很理解。
令我疑惑的是我只是在一个小程序里利用了PWM使用PB4、PB5、PB6、PB7输出，之前有好多次修改debug是没有问题的，但是同样的程序在某一次就突然锁定了，接下来每次就要去解锁。
还有请问我需要怎么做才能避免每次锁定的问题？
谢谢！

JTAG和PC口才是复用的，PB口与其无关，你的代码中是否有对PC口进行操作？如果没有PC配置，那么你这种情况就不确定是什么原因导致的。
烧一个我们简单的例程进去，看看是不是会锁定？
GPIO默认说明在数据手册中有详细说明。

Maka:
谢谢您的耐心解答。
解锁后烧进简单的程序不再锁定，但是我的程序（附件内）里确实没有对PC口操作的，这到底是为什么呢？
谢谢

Maka：
您好！
谢谢您的耐心的解答。
烧进简单程序没有再被锁定，但我的程序（下附）里确实没有对PC口操作的，这是为什么呢？
谢谢
/*利用PWMO,PWM1产生200HZ和400Hz 50%占空比的方波*/
#include
#include
#include "inc/hw_memmap.h"
#include "inc/hw_types.h"
#include "driverlib/sysctl.h"
#include "driverlib/rom.h"
#include "driverlib/gpio.h"
#include "driverlib/pwm.h"
#include "driverlib/fpu.h"
#include "driverlib/pin_map.h"
int main (void)
[
//使能FPU
FPUEnable();
FPULazyStackingEnable();
//设置系统时钟为16MHz
SysCtlClockSet(SYSCTL_SYSDIV_64|SYSCTL_USE_OSC|SYSCTL_OSC_MAIN |SYSCTL_XTAL_16MHZ);
//使能PWM0模块,使能PWM0和PWM1输出所在GPIO
SysCtlPeripheralEnable(SYSCTL_PERIPH_PWM0);
SysCtlPeripheralEnable(SYSCTL_PERIPH_GPIOB);
GPIOPinTypePWM(GPIO_PORTB_BASE, GPIO_PIN_4|GPIO_PIN_5|GPIO_PIN_6|GPIO_PIN_7);
GPIOPinConfigure(GPIO_PB6_M0PWM0);
GPIOPinConfigure(GPIO_PB7_M0PWM1);
GPIOPinConfigure(GPIO_PB4_M0PWM2);
GPIOPinConfigure(GPIO_PB5_M0PWM3);
//驱动电流8MA，推挽输出
GPIOPadConfigSet(GPIO_PORTB_BASE,GPIO_PIN_4|GPIO_PIN_5|GPIO_PIN_6|GPIO_PIN_7,
GPIO_STRENGTH_8MA,GPIO_PIN_TYPE_STD);
// PWM时钟配置
SysCtlPWMClockSet(SYSCTL_PWMDIV_1);
// SysCtlPWMClockSet(SYSCTL_PWMDIV_32);
//配置PWM发生器0：加减计数，不同步
PWMGenConfigure(PWM0_BASE,PWM_GEN_0,PWM_GEN_MODE_UP_DOWN| PWM_GEN_MODE_NO_SYNC);
PWMGenConfigure(PWM0_BASE,PWM_GEN_1,PWM_GEN_MODE_UP_DOWN| PWM_GEN_MODE_NO_SYNC);
//设置PWM发生器0的频率，时钟频率/PWM分频数/n，16M/64/1250=200HZ
PWMGenPeriodSet(PWM0_BASE, PWM_GEN_0, 1250);
//设置PWM发生器1的频率，时钟频率/PWM分频数/n，16M/16/625=400HZ
PWMGenPeriodSet(PWM0_BASE, PWM_GEN_1, 625);
//设置PWM0/PWM1输出的脉冲宽度
PWMPulseWidthSet(PWM0_BASE, PWM_OUT_0,1250/2);
PWMPulseWidthSet(PWM0_BASE, PWM_OUT_1,1250/2);
PWMPulseWidthSet(PWM0_BASE, PWM_OUT_2,625/2);
PWMPulseWidthSet(PWM0_BASE, PWM_OUT_3,625/2);
//使能PWM0和PWM1的输出
PWMOutputState(PWM0_BASE, (PWM_OUT_0_BIT |PWM_OUT_1_BIT| PWM_OUT_2_BIT| PWM_OUT_3_BIT), true);
//使能PWM发生器
PWMGenEnable(PWM0_BASE, PWM_GEN_0);
PWMGenEnable(PWM0_BASE, PWM_GEN_1);
while(1)
[
]
]

从程序代码来看，没有什么问题。
仿真过程中是否有同样的问题？

有的，也是这样

那PWM工作正常？
这有点奇怪，建议换个硬件看看。

测试一下这个例程，看看JTAG是否正常。

模块时钟使能后需要加至少6时钟周期的延时
能否换个硬件看看是否存在同样的问题？