Posted on September 28, 2017 at 06:50
HI.
Now I'm trying to implement TIM into the STM32F429i-DISCO kit.
But I need to help how to calculate the prescaler and period value for user?
As I know currently I used 180Mhz as system clock. and I want to set TIM work every 1 's single second.
What am I suppose to do? the below snippet code I found from google.
But I can't understand what does 6000000 mean?
/* Compute the prescaler value */
PrescalerValue = (uint16_t) ((SystemCoreClock / 2) / 6000000) - 1;/* Time base configuration */TIM_TimeBaseStructure.TIM_Period = (6000-1); //Autoreload value (ARR) -> 1msTIM_TimeBaseStructure.TIM_Prescaler = (6000-1);TIM_TimeBaseStructure.TIM_ClockDivision = 0;TIM_TimeBaseStructure.TIM_CounterMode = TIM_CounterMode_Up;I found some explain from google as the below.
TIM_Prescaler = N - 1; Divides the Bus/TIM clock down by N
TIM_Period = N - 1; Divide that clock down by N, ie the *period* is N ticks.
So assume your TIMCLK is ticking at 72 MHz, the *external* clock
If TIM_Prescaler = 71; the timers *internal* clock
will be 1 MHz
If TIM_Period = 999; the 1MHz is divided by a 1000, so
it becomes 1KHz
Your update interrupt with fire every 1ms
Now if you want to play with the channels, say in a PWM mode you can play with the output pins.
If TIM_Pulse = 500; the channel will out a frequency of 1 KHz, with a 50/50 duty cycle. ie TIM_Pulse = N / 2
How to calculate and know ?
If TIM_Prescaler = 71; the timers *internal* clock
will be 1 MHz
If TIM_Period = 999; the 1MHz is divided by a 1000, so
it becomes 1KHz
How to calculate and know ?
What if
If TIM_Prescaler = 63; the timers *internal* clock
will be ?? MHz
If TIM_Period = 123; the
it becomes ?? KHz
Would you please help me for understanding how to calculate ?
When I set with the following setting, I've got the below waveform.
TIM_TimeBaseStructure.TIM_Period = 71; TIM_TimeBaseStructure.TIM_Prescaler = 999; TIM_TimeBaseStructure.TIM_ClockDivision = 0; TIM_TimeBaseStructure.TIM_CounterMode = TIM_CounterMode_Up; TIM_TimeBaseInit(TIM2, &TIM_TimeBaseStructure);/* TIM Interrupts enable */
TIM_ITConfig(TIM2, TIM_IT_Update, ENABLE);/* TIM2 enable counter */TIM_Cmd(TIM2, ENABLE);
Posted on September 28, 2017 at 22:16
Microchip has something very nice regarding the visual code generator, you can specify the period in milliseconds or microseconds and it shows all the changes, results and generate the right code for you. This should be another improvement/proposal for CubeMX.
Posted on September 29, 2017 at 01:06
Is TIM_CLOCK specified in the datasheet, or is something we can pick from the Configuration Clock diagram in CubeMX (the diagram is for an L152RE)?
Won't be better to have some combobox controls in the ''Parameter Configuration'' window of the Timer, related to the ''things'' already set in the Configuration Clock diagram and related to some named variables in LL/HAL drivers? I'm thinking in the relation with the other comment I have here. And we must see the resulted tick period displayed, to see if we managed to do it right.
