Frequency Measurement with NUCLEO-U575ZI-Q
I'm trying to use the frequency measurement with NUCLEO-U575ZI-Q. As per suggested, the max allowed frequency of SYSCLK is 160 MHz which I use. I'm configuring TIM2 Channel 1 in direct input capture mode. I use 0 as the prescaler and the max value for the counter (but I reset the timer every time I calculate the frequency). I detect the rising edge and I don't use any Input Filter (which could be a 4 bit value).
The strange part is when I try to measure frequencies below 500 KHz, the result is super stable and reliable. I used both a lab function generator and the STM PWM generator via TIM 1 as the input test signal.
However, when I try signals above 800 KHz for testing I read values which are sometimes 800KHz and sometimes 400KHz!
Even stranger, when the input signal is above 1 MHz, I either measure 800KHz or 533.3333KHz!.
I use the IC interrupt to implement my calculations as following. It might me useful to switch to DMA but again, I cannot justify how it is possible not to be able to measure 1 MHz with a 160MHz internal clock!
I have included my interrupt implementation in the following:
void HAL_TIM_IC_CaptureCallback(TIM_HandleTypeDef *htim){
if (htim->Channel == HAL_TIM_ACTIVE_CHANNEL_1)
{
if (Is_First_Captured==0) // if the first rising edge is not captured
{
IC_Val1 = HAL_TIM_ReadCapturedValue(htim, TIM_CHANNEL_1); // read the first value
Is_First_Captured = 1; // set the first captured as true
}
else // If the first rising edge is captured, now we will capture the second edge
{
IC_Val2 = HAL_TIM_ReadCapturedValue(htim, TIM_CHANNEL_1); // read second value
if (IC_Val2 > IC_Val1)
{
Difference = IC_Val2-IC_Val1;
}
else if (IC_Val1 > IC_Val2)
{
Difference = (htim1.Init.Period - IC_Val1) + IC_Val2;
}
float refClock = TIMCLK;
if (Difference != 0){
frequency = refClock/(Difference*(htim2.Init.Prescaler+1));
}
__HAL_TIM_SET_COUNTER(htim, 0); // reset the counter
Is_First_Captured = 0; // set it back to false
}
}
}
For the reference, I'm also providing my TIM2 setting in the following:
static void MX_TIM2_Init(void)
{
/* USER CODE BEGIN TIM2_Init 0 */
/* USER CODE END TIM2_Init 0 */
TIM_ClockConfigTypeDef sClockSourceConfig = {0};
TIM_MasterConfigTypeDef sMasterConfig = {0};
TIM_IC_InitTypeDef sConfigIC = {0};
/* USER CODE BEGIN TIM2_Init 1 */
/* USER CODE END TIM2_Init 1 */
htim2.Instance = TIM2;
htim2.Init.Prescaler = 0;
htim2.Init.CounterMode = TIM_COUNTERMODE_UP;
htim2.Init.Period = 4.294967295E9;
htim2.Init.ClockDivision = TIM_CLOCKDIVISION_DIV1;
htim2.Init.AutoReloadPreload = TIM_AUTORELOAD_PRELOAD_DISABLE;
if (HAL_TIM_Base_Init(&htim2) != HAL_OK)
{
Error_Handler();
}
sClockSourceConfig.ClockSource = TIM_CLOCKSOURCE_INTERNAL;
if (HAL_TIM_ConfigClockSource(&htim2, &sClockSourceConfig) != HAL_OK)
{
Error_Handler();
}
if (HAL_TIM_IC_Init(&htim2) != HAL_OK)
{
Error_Handler();
}
sMasterConfig.MasterOutputTrigger = TIM_TRGO_RESET;
sMasterConfig.MasterSlaveMode = TIM_MASTERSLAVEMODE_DISABLE;
if (HAL_TIMEx_MasterConfigSynchronization(&htim2, &sMasterConfig) != HAL_OK)
{
Error_Handler();
}
sConfigIC.ICPolarity = TIM_INPUTCHANNELPOLARITY_FALLING;
sConfigIC.ICSelection = TIM_ICSELECTION_DIRECTTI;
sConfigIC.ICPrescaler = TIM_ICPSC_DIV1;
sConfigIC.ICFilter = 0;
if (HAL_TIM_IC_ConfigChannel(&htim2, &sConfigIC, TIM_CHANNEL_1) != HAL_OK)
{
Error_Handler();
}
/* USER CODE BEGIN TIM2_Init 2 */
/* USER CODE END TIM2_Init 2 */
}
Finally, my variable definition:
#define TIMCLK 160000000