[参考译文] TM4C123GH6PGE：使用输入捕捉模式的 TimerValueGet ()在 OS 任务延迟下是不准确的。

/* Enable the Timer
	 * Note that the GP Timer module clock must be enabled before the registers can be programmed
	 * (see page 338 or page 357). There must be a delay of 3 system clocks after the Timer module clock
	 * is enabled before any Timer module registers are accessed.
	 */
	MAP_SysCtlPeripheralEnable(SYSCTL_PERIPH_WTIMER1);

	// Set the IO pin to be an input for wide timer
	// Use PC7 which is input 8, which is an ODD input (i.e. TIMER B)
	GPIOPinConfigure(GPIO_PC7_WT1CCP1);
	MAP_GPIOPinTypeTimer(GPIO_PORTC_BASE, GPIO_PIN_7);

	// Configure the timer
	// Capture the time value at each event edge
	MAP_TimerConfigure(WTIMER1_BASE, (TIMER_CFG_SPLIT_PAIR | TIMER_CFG_A_PERIODIC | TIMER_CFG_B_CAP_TIME));

	// Count on Positive Edges
	MAP_TimerControlEvent(WTIMER1_BASE, TIMER_B, TIMER_EVENT_POS_EDGE);

	// The timer starts at 0xFFFFFFFF and counts down.
	MAP_TimerLoadSet(WTIMER1_BASE, TIMER_B, 0x00FFFFFF);
	MAP_TimerMatchSet(WTIMER1_BASE, TIMER_B, 0x00FFFFFE);

	// Configure the prescaler
	// Note: I can not see when this is operating in our split timer mode
	MAP_TimerPrescaleSet(WTIMER1_BASE, TIMER_B, 0xFF);
	MAP_TimerPrescaleMatchSet(WTIMER1_BASE, TIMER_B, 0xFE);

	// Configure the update mode
	TimerUpdateMode(WTIMER1_BASE, TIMER_B, TIMER_UP_LOAD_IMMEDIATE);

	// Clear the interrupt for TIMER_B capture event
	MAP_TimerIntClear(WTIMER1_BASE, TIMER_CAPB_EVENT);

	// Start the timer
	MAP_TimerEnable(WTIMER1_BASE, TIMER_B);

while(1)
	{

		// Check if we have status
		/* Poll the CnERIS bit in the GPTMRIS register or wait for the interrupt to be generated (if enabled).
		 * In both cases, the status flags are cleared by writing a 1 to the CnECINT bit of the GPTM
		 * Interrupt Clear (GPTMICR) register. The time at which the event happened can be obtained
		 * by reading the GPTM Timer n (GPTMTnR) register.
		 */
		u32Status = MAP_TimerIntStatus(WTIMER1_BASE, 0);
		if((u32Status & TIMER_CAPB_EVENT) == TIMER_CAPB_EVENT)
		{
			// Count of timer ticks between pulses
			m_u32RawCount = (Luint32)TimerValueGet(WTIMER1_BASE, TIMER_B);

			// As we are counting down do the difference
			// It may be that the variant of the CPU we use does not have an up-counter function?
			u32Diff = (0xFFFFFFFF - m_u32RawCount);

			// Work out the difference
			m_u32TimerCount = u32Diff - u32TempPrev;

			// Save the prev value
			u32TempPrev = u32Diff;

			// Clear the flag again for next time
			MAP_TimerIntClear(WTIMER1_BASE, TIMER_CAPB_EVENT);

		}

		vTaskDelay(pdMS_TO_TICKS(1));
	}