[参考译文] EK-TM4C1294XL：EK-TM4C1294XL

您好！

  为了增加频率，您需要直接写入 GPIO 数据寄存器，因为 GPIOPinWrite()函数在写入数据之前执行一些移位运算来计算地址。 您 的 g_ui32Flags = 1 - g_ui32Flags 也需要一些周期来完成。  查看反汇编窗口、您可以找到生成的汇编指令并推算所需的周期数。  如果您知道要写入的确切值和寄存器地址、则可以通过如下方式直接写入寄存器来降低延迟：

 HWREG (GPIOPx_ADDR、0x55)；//示例写入值为0x55的任意地址 GPIOx_ADDR

但是、您永远无法精确地确定您将获得的频率。 要获得一致的5MHz 频率、您应生成 PWM 信号。 定时器模块可被配置为 PWM。 您所需的只是设置周期和占空比、为您提供所需的5MHz 周期性信号。

请参阅示例 C：\ti\TivaWare_C_Series-2.2.0.295\examples\peripheral\timer\PWM.c

无效
GPIOPinWrite (uint32_t ui32Port、uint8_t ui8引脚、uint8_t ui8Val)
｛
//
//检查参数。
//
assert (_GPIOBaseValid (ui32Port))；

//
//写入引脚。
//
HWREG (ui32Port +(GPIO_O_DATA +(ui8引脚<< 2)))= ui8Val；
｝

下面是一个5MHz PWM 示例。 PWM 周期为5MHz、占空比在25%和75%之间变化。  

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


//*****************************************************************************
//
// The variable g_ui32SysClock contains the system clock frequency in Hz.
//
//*****************************************************************************
uint32_t g_ui32SysClock;

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


//*****************************************************************************
//
// Configure PWM for a 25% duty cycle signal running at 250Hz.
//
//*****************************************************************************
int
main(void)
{
    uint32_t ui32PWMClockRate;

    //
    // Run from the PLL at 120 MHz.
    // Note: SYSCTL_CFG_VCO_240 is a new setting provided in TivaWare 2.2.x and
    // later to better reflect the actual VCO speed due to SYSCTL#22.
    //
    g_ui32SysClock = MAP_SysCtlClockFreqSet((SYSCTL_XTAL_25MHZ |
                                             SYSCTL_OSC_MAIN |
                                             SYSCTL_USE_PLL |
                                             SYSCTL_CFG_VCO_240), 120000000);


    //
    // The PWM peripheral must be enabled for use.
    //
    MAP_SysCtlPeripheralEnable(SYSCTL_PERIPH_PWM0);

    //
    // Enable the GPIO port that is used for the PWM output.
    //
    MAP_SysCtlPeripheralEnable(SYSCTL_PERIPH_GPIOF);

    //
    // Configure the PWM function for this pin.
    //
    MAP_GPIOPinConfigure(GPIO_PF2_M0PWM2);
    MAP_GPIOPinTypePWM(GPIO_PORTF_BASE, GPIO_PIN_2);

    //
    // Set the PWM clock to be SysClk / 8.
    //
    MAP_PWMClockSet(PWM0_BASE, PWM_SYSCLK_DIV_1);
    //
    // Use a local variable to store the PWM clock rate which will be
    // 120 MHz / 8 = 15 MHz. This variable will be used to set the
    // PWM generator period.
    //
    ui32PWMClockRate = g_ui32SysClock / 1;

    //
    // Configure PWM2 to count up/down without synchronization.
    //
    MAP_PWMGenConfigure(PWM0_BASE, PWM_GEN_1,
                        PWM_GEN_MODE_UP_DOWN | PWM_GEN_MODE_NO_SYNC);

    //
    // Set the PWM period to 5Mhz.  To calculate the appropriate parameter
    // use the following equation: N = (1 / f) * PWMClk.  Where N is the
    // function parameter, f is the desired frequency, and PWMClk is the
    // PWM clock frequency based on the system clock.
    //
    MAP_PWMGenPeriodSet(PWM0_BASE, PWM_GEN_1, (ui32PWMClockRate / 5000000));

    //
    // Set PWM2 to a duty cycle of 25%.  You set the duty cycle as a function
    // of the period.  Since the period was set above, you can use the
    // PWMGenPeriodGet() function.  For this example the PWM will be high for
    // 25% of the time or (PWM Period / 4).
    //
    MAP_PWMPulseWidthSet(PWM0_BASE, PWM_OUT_2,
                         MAP_PWMGenPeriodGet(PWM0_BASE, PWM_GEN_1) / 4);

    //
    // Enable PWM Out Bit 2 (PF2) output signal.
    //
    MAP_PWMOutputState(PWM0_BASE, PWM_OUT_2_BIT, true);

    //
    // Enable the PWM generator block.
    //
    MAP_PWMGenEnable(PWM0_BASE, PWM_GEN_1);

    //
    // Loop forever while the PWM signals are generated.
    //
    while(1)
    {
        //
        // This function provides a means of generating a constant length
        // delay.  The function delay (in cycles) = 3 * parameter.  Delay
        // 2 seconds arbitrarily.
        //
        MAP_SysCtlDelay((g_ui32SysClock * 2) / 3);

        //
        // Invert PWM2 signal.
        //
        MAP_PWMOutputInvert(PWM0_BASE, PWM_OUT_2_BIT, true);

        //
        // This function provides a means of generating a constant length
        // delay.  The function delay (in cycles) = 3 * parameter.  Delay
        // 2 seconds arbitrarily.
        //
        MAP_SysCtlDelay((g_ui32SysClock * 2) / 3);

        //
        // Switch PWM2 signal back to regular operation.
        //
        MAP_PWMOutputInvert(PWM0_BASE, PWM_OUT_2_BIT, false);
    }
}

如果您希望使用计时器模块生成 PWM、下面是另一个生成5MHz PWM 的示例。  

#include <stdbool.h>
#include <stdint.h>
#include "inc/hw_gpio.h"
#include "inc/hw_ints.h"
#include "inc/hw_memmap.h"
#include "inc/hw_timer.h"
#include "inc/hw_types.h"
#include "driverlib/gpio.h"
#include "driverlib/interrupt.h"
#include "driverlib/pin_map.h"
#include "driverlib/sysctl.h"
#include "driverlib/timer.h"
#include "driverlib/uart.h"
#include "utils/uartstdio.h"


//*****************************************************************************
//
// The g_ui32SysClock contains the system clock frequency
//
//*****************************************************************************

uint32_t g_ui32SysClock;


//*****************************************************************************
//
// Configure Timer3A as a 16-bit PWM with a duty cycle of 66%.
//
//*****************************************************************************
int
main(void)
{
    //
    // Set the clocking to run directly from the external crystal/oscillator.
    // TODO: The SYSCTL_XTAL_ value must be changed to match the value of the
    // crystal on your board.
    //

    g_ui32SysClock = SysCtlClockFreqSet((SYSCTL_XTAL_25MHZ |
                                       SYSCTL_OSC_MAIN |
                                       SYSCTL_USE_PLL |
                                       SYSCTL_CFG_VCO_480), 120000000);

    //
    // The Timer1 peripheral must be enabled for use.
    //
    SysCtlPeripheralEnable(SYSCTL_PERIPH_TIMER3);

    //
    // For this example T3CCP0 is used with port B pin 2 or port M pin 2.
    // The actual port and pins used may be different on your part, consult
    // the data sheet for more information.
    // GPIO port B needs to be enabled so these pins can be used.
    // TODO: change this to whichever GPIO port you are using.
    //

    SysCtlPeripheralEnable(SYSCTL_PERIPH_GPIOM);

    //
    // Configure the GPIO pin muxing for the Timer/CCP function.
    // This is only necessary if your part supports GPIO pin function muxing.
    // Study the data sheet to see which functions are allocated per pin.
    // TODO: change this to select the port/pin you are using
    //
    GPIOPinConfigure(GPIO_PM2_T3CCP0);

    //
    // Configure the ccp settings for CCP pin.  This function also gives
    // control of these pins to the SSI hardware.  Consult the data sheet to
    // see which functions are allocated per pin.
    // TODO: change this to select the port/pin you are using.
    //
    GPIOPinTypeTimer(GPIO_PORTM_BASE, GPIO_PIN_2);

    //
    // Configure Timer3A as a 16-bit periodic timer.
    //
    TimerConfigure(TIMER3_BASE, TIMER_CFG_SPLIT_PAIR | TIMER_CFG_A_PWM);

    //
    // Set the Timer3A load value to (120000000/5000000=24) - 1
    //
    TimerLoadSet(TIMER3_BASE, TIMER_A, g_ui32SysClock / 5000000 - 1);

    //
    // Set the Timer3A match value to load value / 2.
    //
    TimerMatchSet(TIMER3_BASE, TIMER_A,
                  TimerLoadGet(TIMER3_BASE, TIMER_A) / 2);

    //
    // Enable Timer3A.
    //
    TimerEnable(TIMER3_BASE, TIMER_A);

    //
    // Loop forever while the Timer3A PWM runs.
    //
    while(1)
    {

    }
}