Timer Frequency is not predictable

[vbk22398]

I am using STM32L496ZGT6P. When using DAC along with DMA to generate voltage and frequency of my desired range. But I am unable to get hold of the frequency setting. Sysclk I set is 4Mhz. 20 is prescaler value, 4Mhz/20 = 200000.This is further divided by 10 which is time period(ARR) .I am supposed to get 20000 as output in DAC, which I am getting in UART because of the below function, but I am not getting that in CRO. in CRO I am getting 100Hz when I tap DAC output. I have cross checked the output of the DAC using multimeter also. I am getting 100Hz in multimeter. I am unable to figure it out where is the mistake. So any help in this regard is greatly appreciated.

uint32_t Get_Timer2_Frequency(void)
{
   pclk1 = HAL_RCC_GetPCLK1Freq(); 

   prescaler = ((RCC->CFGR & RCC_CFGR_PPRE1) >> RCC_CFGR_PPRE1_Pos);
   timer_clock = pclk1;

   if (prescaler != 0) { 
        timer_clock = 2 * pclk1;
   }

   timer_prescaler = htim2.Instance->PSC; 

   period = htim2.Instance->ARR;

   timer_frequency = timer_clock / ((timer_prescaler + 1)* (period + 1));

   return timer_frequency;
}


Below is my Sysclkconfig function.

void SystemClock_Config(void)
{
RCC_OscInitTypeDef RCC_OscInitStruct = {0};
RCC_ClkInitTypeDef RCC_ClkInitStruct = {0};

/** Configure the main internal regulator output voltage
*/
if (HAL_PWREx_ControlVoltageScaling(PWR_REGULATOR_VOLTAGE_SCALE1) != HAL_OK)
{
Error_Handler();
}

/** Initializes the RCC Oscillators according to the specified parameters
* in the RCC_OscInitTypeDef structure.
*/
RCC_OscInitStruct.OscillatorType = RCC_OSCILLATORTYPE_HSI;
RCC_OscInitStruct.HSIState = RCC_HSI_ON;
RCC_OscInitStruct.HSICalibrationValue = RCC_HSICALIBRATION_DEFAULT;
RCC_OscInitStruct.PLL.PLLState = RCC_PLL_NONE;
if (HAL_RCC_OscConfig(&RCC_OscInitStruct) != HAL_OK)
{
Error_Handler();
}

/** Initializes the CPU, AHB and APB buses clocks
*/
RCC_ClkInitStruct.ClockType = RCC_CLOCKTYPE_HCLK|RCC_CLOCKTYPE_SYSCLK
|RCC_CLOCKTYPE_PCLK1|RCC_CLOCKTYPE_PCLK2;
RCC_ClkInitStruct.SYSCLKSource = RCC_SYSCLKSOURCE_HSI;
RCC_ClkInitStruct.AHBCLKDivider = RCC_SYSCLK_DIV4;
RCC_ClkInitStruct.APB1CLKDivider = RCC_HCLK_DIV1;
RCC_ClkInitStruct.APB2CLKDivider = RCC_HCLK_DIV1;

if (HAL_RCC_ClockConfig(&RCC_ClkInitStruct, FLASH_LATENCY_0) != HAL_OK)
{
Error_Handler();
}
}

Below is my timer init function:

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};

/* USER CODE BEGIN TIM2_Init 1 */

/* USER CODE END TIM2_Init 1 */
htim2.Instance = TIM2;
htim2.Init.Prescaler = 20-1;
htim2.Init.CounterMode = TIM_COUNTERMODE_UP;
htim2.Init.Period = 10-1;
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();
}
sMasterConfig.MasterOutputTrigger = TIM_TRGO_UPDATE;
sMasterConfig.MasterSlaveMode = TIM_MASTERSLAVEMODE_DISABLE;
if (HAL_TIMEx_MasterConfigSynchronization(&htim2, &sMasterConfig) != HAL_OK)
{
Error_Handler();
}
/* USER CODE BEGIN TIM2_Init 2 */

/* USER CODE END TIM2_Init 2 */

}
 
below is my main:

int main(void)
{

/* USER CODE BEGIN 1 */

/* USER CODE END 1 */

/* MCU Configuration--------------------------------------------------------*/

/* Reset of all peripherals, Initializes the Flash interface and the Systick. */
HAL_Init();

/* USER CODE BEGIN Init */

/* USER CODE END Init */

/* Configure the system clock */
SystemClock_Config();

/* USER CODE BEGIN SysInit */

/* USER CODE END SysInit */

/* Initialize all configured peripherals */
MX_GPIO_Init();
MX_DMA_Init();
MX_DAC1_Init();
MX_LPUART1_UART_Init();
MX_TIM2_Init();

/* USER CODE BEGIN 2 */
HAL_TIM_Base_Start(&htim2);
gen_sine(array, OUTPUT_2_5);
HAL_DAC_Start_DMA(&hdac1, DAC_CHANNEL_1, (uint32_t*) array, NP,DAC_ALIGN_12B_R);

data = Get_Timer2_Frequency();

memset((uint8_t*) TxData, 0, 15);

sprintf(TxData, "%u\r\n", data);
HAL_UART_Transmit(&hlpuart1, TxData, 15, HAL_MAX_DELAY);

while (1) {

/* USER CODE END WHILE */

/* USER CODE BEGIN 3 */
}
/* USER CODE END 3 */
}
}

[vbk22398 · Accepted solution]

void calculate_DAC_OUTPUT_Freq(void)
{
sysclk = HAL_RCC_GetSysClockFreq();
//uint32_t data = SystemCoreClock;

pclk1 = HAL_RCC_GetPCLK1Freq();

prescaler_bits = (RCC->CFGR & RCC_CFGR_PPRE1) >> RCC_CFGR_PPRE1_Pos;

timer_clock = pclk1;

if (prescaler_bits != 0) {
timer_clock = 2 * pclk1;
}

timer_prescaler = htim2.Instance->PSC;
period = htim2.Instance->ARR;

timer_frequency = (double) timer_clock/ ((timer_prescaler + 1) * (period + 1));

dac_output_frequency = timer_frequency / NP;
}

The above function answers the question. I didn't spend enough time on how to find the frequency of the DAC. It was a trivial question!