Hello,
i have a simple task which turned to be more tricky than i expected.
The system uses a 8mhz HSE.
My clocks are :
HCLK/SYSCLK is 100MHZ
PCLK1 is 25MHZ
PCLK2 is 50 MHZ ( 100MHZ for TIM1)
I need to generate a 50% duty 100khz PWM signal via PE9 pin ( channel1 from TIMER1).
As i know the timer tick is tick = ( 1/(PCLK *2) ) * Prescale - 1 , the pwm frequency is 1/(tick * Preload)
Therefore for 100MHZ input, and for a PSC of 100 (101-1) and Period of 10 (11-1) i would expect a 100kHZ pwm signal, but the actual frequency is 81.2khz.
Why this huge diference? I also tried with lower frequencies, and the result is the same
I will show you the actual code
int main(void)
{
SystemInit();
RCC_ClocksTypeDef clocks;
RCC_GetClocksFreq(&clocks);
// uint32_t hs = HSE_VALUE;
RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOE, ENABLE);
RCC_APB2PeriphClockCmd(RCC_APB2Periph_TIM1, ENABLE);
GPIO_InitTypeDef GPIO_InitStruct;
TIM_TimeBaseInitTypeDef TIM_TimeBaseStructure;
TIM_OCInitTypeDef TIM_OCInitStructure;
GPIO_InitStruct.GPIO_Pin = GPIO_Pin_9 ;
GPIO_InitStruct.GPIO_Mode = GPIO_Mode_AF;
GPIO_InitStruct.GPIO_OType = GPIO_OType_PP;
GPIO_InitStruct.GPIO_Speed = GPIO_Speed_100MHz;
GPIO_InitStruct.GPIO_PuPd = GPIO_PuPd_UP;
GPIO_Init(GPIOE, &GPIO_InitStruct);
GPIO_PinAFConfig(GPIOE, GPIO_PinSource9, GPIO_AF_TIM1);
TIM_TimeBaseStructure.TIM_Prescaler = 101;
TIM_TimeBaseStructure.TIM_CounterMode = TIM_CounterMode_Up;
TIM_TimeBaseStructure.TIM_Period = 11;
TIM_TimeBaseStructure.TIM_ClockDivision = 0;
TIM_TimeBaseStructure.TIM_RepetitionCounter = 0;
TIM_TimeBaseInit(TIM1, &TIM_TimeBaseStructure);
TIM_OCInitStructure.TIM_OCMode = TIM_OCMode_PWM1;//
TIM_OCInitStructure.TIM_OutputState = TIM_OutputState_Enable;
TIM_OCInitStructure.TIM_Pulse =5; // 50 %duty
TIM_OCInitStructure.TIM_OCPolarity = TIM_OCPolarity_High;
TIM_OC1Init(TIM1, &TIM_OCInitStructure);
TIM_OC1PreloadConfig(TIM1, TIM_OCPreload_Enable);
TIM_ARRPreloadConfig(TIM1, ENABLE);
TIM_Cmd(TIM1, ENABLE);
TIM_CtrlPWMOutputs(TIM1, ENABLE);
return 0;
}
