STM32F303ZE: PWM has only half the frequency

Question

I'm currently working myself into STM32 programming for a project. For this project I need to produce a 20kHz (=f_pwm) center-aligned PWM. Using CubeMX I set the TIM1 clk to 144 MHz (=f_tim) by using the PLLCLK*2. Then I proceeded by setting the ARR register to period=f_tim/(2*f_pwm). The *2 is from the center-aligned mode, since it counts up and down. After programming the STM32 with those parameters, I'm only getting 10 kHz (measured on a scope). My calculation and the clock settings seem to be correct (checked through the generated code and written registers as well), so I'm out of ideas now. Did anybody already encounter such a problem or knows what the cause might be? Apprehended find my CubeMX clock config and the corresponding code parts.

Thanks to everyone having a look into it!

CubeMX clock config

System Clock Config:

 void SystemClock_Config(void)
{
 RCC_OscInitTypeDef RCC_OscInitStruct;
 RCC_ClkInitTypeDef RCC_ClkInitStruct;
 RCC_PeriphCLKInitTypeDef PeriphClkInit;
 /**Initializes the CPU, AHB and APB busses clocks 
 */
 RCC_OscInitStruct.OscillatorType = RCC_OSCILLATORTYPE_HSI;
 RCC_OscInitStruct.HSIState = RCC_HSI_ON;
 RCC_OscInitStruct.HSICalibrationValue = 16;
 RCC_OscInitStruct.PLL.PLLState = RCC_PLL_ON;
 RCC_OscInitStruct.PLL.PLLSource = RCC_PLLSOURCE_HSI;
 RCC_OscInitStruct.PLL.PLLMUL = RCC_PLL_MUL9;
 RCC_OscInitStruct.PLL.PREDIV = RCC_PREDIV_DIV1;
 if (HAL_RCC_OscConfig(&RCC_OscInitStruct) != HAL_OK)
 {
 _Error_Handler(__FILE__, __LINE__);
 }
 /**Initializes the CPU, AHB and APB busses clocks 
 */
 RCC_ClkInitStruct.ClockType = RCC_CLOCKTYPE_HCLK|RCC_CLOCKTYPE_SYSCLK
 |RCC_CLOCKTYPE_PCLK1|RCC_CLOCKTYPE_PCLK2;
 RCC_ClkInitStruct.SYSCLKSource = RCC_SYSCLKSOURCE_PLLCLK;
 RCC_ClkInitStruct.AHBCLKDivider = RCC_SYSCLK_DIV1;
 RCC_ClkInitStruct.APB1CLKDivider = RCC_HCLK_DIV2;
 RCC_ClkInitStruct.APB2CLKDivider = RCC_HCLK_DIV1;
 if (HAL_RCC_ClockConfig(&RCC_ClkInitStruct, FLASH_LATENCY_2) != HAL_OK)
 {
 _Error_Handler(__FILE__, __LINE__);
 }
 PeriphClkInit.PeriphClockSelection = RCC_PERIPHCLK_USART3|RCC_PERIPHCLK_TIM1
 |RCC_PERIPHCLK_ADC12|RCC_PERIPHCLK_ADC34
 |RCC_PERIPHCLK_TIM20;
 PeriphClkInit.Usart3ClockSelection = RCC_USART3CLKSOURCE_PCLK1;
 PeriphClkInit.Adc12ClockSelection = RCC_ADC12PLLCLK_DIV64;
 PeriphClkInit.Adc34ClockSelection = RCC_ADC34PLLCLK_DIV64;
 PeriphClkInit.Tim1ClockSelection = RCC_TIM1CLK_PLLCLK;
 PeriphClkInit.Tim20ClockSelection = RCC_TIM20CLK_PLLCLK;
 if (HAL_RCCEx_PeriphCLKConfig(&PeriphClkInit) != HAL_OK)
 {
 _Error_Handler(__FILE__, __LINE__);
 }
 /**Configure the Systick interrupt time 
 */
 HAL_SYSTICK_Config(HAL_RCC_GetHCLKFreq()/1000);
 /**Configure the Systick 
 */
 HAL_SYSTICK_CLKSourceConfig(SYSTICK_CLKSOURCE_HCLK);
 /* SysTick_IRQn interrupt configuration */
 HAL_NVIC_SetPriority(SysTick_IRQn, 0, 0);
}

TIM1 Init:

void MX_TIM1_Init(void)
{
 TIM_ClockConfigTypeDef sClockSourceConfig;
 TIM_MasterConfigTypeDef sMasterConfig;
 TIM_OC_InitTypeDef sConfigOC;
 TIM_BreakDeadTimeConfigTypeDef sBreakDeadTimeConfig;
 htim1.Instance = TIM1;
 htim1.Init.Prescaler = 1;
 htim1.Init.CounterMode = TIM_COUNTERMODE_CENTERALIGNED3;
 htim1.Init.Period = 3600;
 htim1.Init.ClockDivision = TIM_CLOCKDIVISION_DIV1;
 htim1.Init.RepetitionCounter = 0;
 htim1.Init.AutoReloadPreload = TIM_AUTORELOAD_PRELOAD_DISABLE;
 if (HAL_TIM_Base_Init(&htim1) != HAL_OK)
 {
 _Error_Handler(__FILE__, __LINE__);
 }
 sClockSourceConfig.ClockSource = TIM_CLOCKSOURCE_INTERNAL;
 if (HAL_TIM_ConfigClockSource(&htim1, &sClockSourceConfig) != HAL_OK)
 {
 _Error_Handler(__FILE__, __LINE__);
 }
 if (HAL_TIM_PWM_Init(&htim1) != HAL_OK)
 {
 _Error_Handler(__FILE__, __LINE__);
 }
 sMasterConfig.MasterOutputTrigger = TIM_TRGO_RESET;
 sMasterConfig.MasterOutputTrigger2 = TIM_TRGO2_RESET;
 sMasterConfig.MasterSlaveMode = TIM_MASTERSLAVEMODE_DISABLE;
 if (HAL_TIMEx_MasterConfigSynchronization(&htim1, &sMasterConfig) != HAL_OK)
 {
 _Error_Handler(__FILE__, __LINE__);
 }
 sConfigOC.OCMode = TIM_OCMODE_PWM1;
 sConfigOC.Pulse = 0;
 sConfigOC.OCPolarity = TIM_OCPOLARITY_HIGH;
 sConfigOC.OCNPolarity = TIM_OCNPOLARITY_HIGH;
 sConfigOC.OCFastMode = TIM_OCFAST_DISABLE;
 sConfigOC.OCIdleState = TIM_OCIDLESTATE_RESET;
 sConfigOC.OCNIdleState = TIM_OCNIDLESTATE_RESET;
 if (HAL_TIM_PWM_ConfigChannel(&htim1, &sConfigOC, TIM_CHANNEL_3) != HAL_OK)
 {
 _Error_Handler(__FILE__, __LINE__);
 }
 sBreakDeadTimeConfig.OffStateRunMode = TIM_OSSR_DISABLE;
 sBreakDeadTimeConfig.OffStateIDLEMode = TIM_OSSI_DISABLE;
 sBreakDeadTimeConfig.LockLevel = TIM_LOCKLEVEL_OFF;
 sBreakDeadTimeConfig.DeadTime = 0;
 sBreakDeadTimeConfig.BreakState = TIM_BREAK_DISABLE;
 sBreakDeadTimeConfig.BreakPolarity = TIM_BREAKPOLARITY_HIGH;
 sBreakDeadTimeConfig.BreakFilter = 0;
 sBreakDeadTimeConfig.Break2State = TIM_BREAK2_DISABLE;
 sBreakDeadTimeConfig.Break2Polarity = TIM_BREAK2POLARITY_HIGH;
 sBreakDeadTimeConfig.Break2Filter = 0;
 sBreakDeadTimeConfig.AutomaticOutput = TIM_AUTOMATICOUTPUT_DISABLE;
 if (HAL_TIMEx_ConfigBreakDeadTime(&htim1, &sBreakDeadTimeConfig) != HAL_OK)
 {
 _Error_Handler(__FILE__, __LINE__);
 }
 HAL_TIM_MspPostInit(&htim1);
}

Set CCR and start PWM:

//Sets TIM_CCR (Compares to counter value), From _hal_tim_ex.h:921
 __HAL_TIM_SET_COMPARE(&htim1,TIM_CHANNEL_3,1800);
 //Start PWM
 HAL_TIM_PWM_Start_IT(&htim1,TIM_CHANNEL_3);

• Matthias: Just solved it myself: I had the Prescaler set to 1 (well, f_tim/1 = f_tim, right?). After setting it to 0 I got the desired f_pwm. From that I'll assume that a prescale of 0 gives the actual PLLCLK*2 and a prescaler >0 gives a timer clock derived fro PLLCLK (which is also SYSCLK). Thanks anyways to anyone who might've invested his time into this problem!
• Matthias: Another comment: Checked the corresponding register PSC in the datasheet and found this one: fCK_PSC / (PSC[15:0] + 1). Kind of interesting, that the actual prescale is the set value+1.
• MemAllox: You might want to formulate an answer and accept it to help other people find the solutions for their problems easier :)

Answer 1

Just solved it myself: I had the Prescaler (Register TIMx_PSC) set to 1 (logically thinking, f_tim/1 = f_tim, right?). After setting it to 0 I got the desired f_pwm. I then digged into my STM's data sheet and found out, that f_tim is calculated as follows: f_tim = f_clk / (PSC+1). Therefore: Prescale set to 0 gives a prescale of 1, set to 1 gives 2 etc.