IWDG with LSI on STM32L0

Hi,

a sample code you can find in ST examples (ex. STM32Cube_FW_F0_V1.7.0/Projects/STM32F042K6-Nucleo/Examples/IWDG/IWDG_Reset/). Basically, you need to configure the timer as input capture, then measure two rising edges and compute the frequency. In the example is it nicely shown. I use Cube generator for the basic code structure so here is generated output:

tim.c

void MX_TIM21_Init(void)
{
 TIM_MasterConfigTypeDef sMasterConfig;
 TIM_IC_InitTypeDef sConfigIC;
 htimInstance = TIM21;
 htimInit.Prescaler = 0;
 htimInit.CounterMode = TIM_COUNTERMODE_UP;
 htimInit.Period = 65535;
 htimInit.ClockDivision = TIM_CLOCKDIVISION_DIV1;
 if (HAL_TIM_IC_Init(&htim21) != HAL_OK)
 {
 Error_Handler();
 }
 sMasterConfig.MasterOutputTrigger = TIM_TRGO_RESET;
 sMasterConfig.MasterSlaveMode = TIM_MASTERSLAVEMODE_DISABLE;
 if (HAL_TIMEx_MasterConfigSynchronization(&htim21, &sMasterConfig) != HAL_OK)
 {
 Error_Handler();
 }
 sConfigIC.ICPolarity = TIM_INPUTCHANNELPOLARITY_RISING;
 sConfigIC.ICSelection = TIM_ICSELECTION_DIRECTTI;
 sConfigIC.ICPrescaler = TIM_ICPSC_DIV8;
 sConfigIC.ICFilter = 0;
 if (HAL_TIM_IC_ConfigChannel(&htim21, &sConfigIC, TIM_CHANNEL_1) != HAL_OK)
 {
 Error_Handler();
 }
 if (HAL_TIMEx_RemapConfig(&htim21, TIM21_TI1_MCO) != HAL_OK)
 {
 Error_Handler();
 }
}�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?

The interrupt is in msp file.

Computation is done in TIM_IC_CaptureCallback like this

void HAL_TIM_IC_CaptureCallback(TIM_HandleTypeDef *htim)
{
 uint32_t lsiperiod = 0;
 /* Get the Input Capture value */
 tmpCC4[uwCaptureNumber++] = HAL_TIM_ReadCapturedValue(&Input_Handle, TIM_CHANNEL_1);
 if (uwCaptureNumber >= 2)
 {
 /* Compute the period length */
 lsiperiod = (uint16_t)(0xFFFF - tmpCC4[0] + tmpCC4[1] + 1);
 /* Frequency computation */ 
 uwLsiFreq = (uint32_t) SystemCoreClock / lsiperiod;
 uwLsiFreq *= 8;
 }
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Required variables for computation are defined as

uint16_t tmpCC4[2] = {0, 0};
__IO uint32_t uwLsiFreq = 0;
__IO uint32_t uwCaptureNumber = 0;�?�?�?

And finally start the timer to measure the frequency

HAL_TIM_IC_Start_IT(&Input_Handle, TIM_CHANNEL_1);
while(uwCaptureNumber < 2);
HAL_TIM_IC_Stop_IT(&Input_Handle, TIM_CHANNEL_1);�?�?�?

Hi,

the LSI is the only clock source option for the IWDG, because it has to be independent on the core frequency and its source. Thus it will be working even if the main clock fails. With HSE and timer combination you will measure the LSI frequency very precisely.