STM32F303ZE: PWM has only half the frequency - stm32

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);

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.