I am setting up Timer 1 channel 3 on the STM32F4. I am looking to set up a period of 3.9ms or 256kHz. I am using ABP1 - 168kHz, the ARR is set to 65535, and a prescaler of 10.
65535 / ( 168,000,000 / 10) = 3.9ms
My timer initialization is below.
_timData.timer_ptr = timx_Ptr;
_timData.timerChannel = Channel; //3
_timData.duty_pct = 0U;
_timData.timPeriod_ticks = TimerPeriod_ticks; // 65535
TIM_TimeBaseInitTypeDef timeBaseStructure =
{
.TIM_Prescaler = Prescaler, //10
.TIM_CounterMode = TIM_CounterMode_Up,
.TIM_Period = _timData.timPeriod_ticks,
.TIM_ClockDivision = TIM_CKD_DIV1,
.TIM_RepetitionCounter = RepetitionCounter, // 0
};
TIM_TimeBaseInit( _timData.timer_ptr, &timeBaseStructure );
// Set up the PWM output init structure.
_timData.ocConfig.TIM_OCMode = TIM_OCMode_PWM1;
_timData.ocConfig.TIM_OutputState = TIM_OutputState_Enable;
_timData.ocConfig.TIM_Pulse = 0U;
_timData.ocConfig.TIM_OCPolarity = TIM_OCPolarity_High;
// initialize channel 3
TIM_OC3Init( _timData.timer_ptr, &_timData.ocConfig );
// Enable the channel's preload register
TIM_OC3PreloadConfig( _timData.timer_ptr, TIM_OCPreload_Enable ); // Channel 3
TIM_InternalClockConfig( _timData.timer_ptr );
TIM_CtrlPWMOutputs( _timData.timer_ptr, ENABLE );
TIM_Cmd( _timData.timer_ptr, ENABLE );
I have confirmed that the configuration registers do not change after initialization. I would expect to see a 3.9ms period, I consistently measure a period of 4.3ms with my scope. The only way I can get a 3.9ms period is altering the prescaler to 9 instead of 10. I do not understand why this is happening and what configuration within the timer controls this. This issue is independent of the CCR register.
This scope captures the signal at a 50% duty cycle and the configuration shown above. I am quite lost on why this is happening.
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