Use timer base and input capture at the same time

[Yuan1]

I use timer gated mode for a HC-SR04 ultrasonic sensor which needs microsecond delay. Is it possible to use the same timer as time base to get microseconds?

if (HAL_TIM_Base_Start(&htim3) != HAL_OK) // time base for usDelay()
		Error_Handler();
if (HAL_TIM_IC_Start_IT(&htim3, TIM_CHANNEL_2) != HAL_OK) // ECHO
		Error_Handler();
...
 
void usDelay (uint16_t uSec)
{
	__HAL_TIM_SET_COUNTER(&htim3, 0);
	while (__HAL_TIM_GET_COUNTER(&htim3) < uSec);
}

The code stuck here.

while (__HAL_TIM_GET_COUNTER(&htim3) < uSec);

[TDK]

Modifying the counter will make your IC readings useless.

However, you can implement the delay without resetting the counter by using the defined overflow behavior. Assuming your counter goes from 0 to 65535:

void usDelay (uint16_t uSec)
{
 uint16_t start = __HAL_TIM_GET_COUNTER(&htim3);
 while ((__HAL_TIM_GET_COUNTER(&htim3) - start) & 0xFFFF <= uSec);
}

You want "<=" to ensure the delay is at least as long as your request. If you use "<" it may be shorter by up to 1us.

A better idea would be to use DWT->CYCCNT counter for highest precision.

[TDK]

> gated mode

Delay is going to work unless your timer is running. It's unclear how you're gating it, but it needs to be free running to be used as a clock source for a delay.

[Yuan1]

Thanks, TDK. Your code worked. I also tried DWT, but it only works in debug mode.

[TDK]

DWT works in any mode, although you do need to enable it first.

[Yuan1]

You are right. DWT also works in nondebug mode. Just found out that I forgot to init DWT.

void DWT_Init(void)
{
 if (!(CoreDebug->DEMCR & CoreDebug_DEMCR_TRCENA_Msk)) {
 CoreDebug->DEMCR |= CoreDebug_DEMCR_TRCENA_Msk;
 DWT->CYCCNT = 0;
 DWT->CTRL |= DWT_CTRL_CYCCNTENA_Msk;
 }
}