STM32F4 Discovery change timer ARR on the fly

anze2 · ‎2014-12-10

Posted on December 10, 2014 at 18:41

Hello everyone!

I am experiencing problem with my discovery board.

I am trying to accelerate my stepper motor, so when i push the button, i decrease value in TIM2 ARR with this command:

uSeconds-=20;

TIM_SetAutoreload(TIM2, uSeconds);

TIM2 is configured so that every 1 unit in arr means 1uS.

So when i push the button, i decrease value in ARR and stepper motor speeds up.

This actualy works, but when i push multiple times, the motor stops (so timere stops giving impulses).

Where is the problem?

The same thing hapens, when i try to accelerate the motor with other timer, so every 1ms tim4 changes ARR value of tim2. For some time it actually accelerates, but then it stops....And at random time...

I am very confused about this and i would really appreciate your help!

Thanks in advance!

Anže

Tesla DeLorean · ‎2014-12-10

Posted on December 10, 2014 at 18:52

Do you implement any limits (high/low) so you don't exceed the specifications of the motor, or the counter?

Do you debounce the button press, or display any of the numbers being written to the register?

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anze2 · ‎2014-12-10

Posted on December 10, 2014 at 19:08

Whoa, that was fast answer, thank you! 🙂

Limits on the counter? Counter is 32 bit, i have values between 200 and 2000 so 200uS and 2000uS...

When i manually set the arr to 200, motor rotates very fast, but it is stable, same thing when i manually set it to 2000 it rotates stable but slow, so it's not the motor limitation i guess.

Button press doesn't need to be debounced, because i use bluetooth USART interrupt from android application (button 'U' means up and 'D' menas down) instead of physical buttons.

I am working on this problem for 1 week and i still didn't figure this out. Any other ideas?

waclawek.jan · ‎2014-12-10

Posted on December 10, 2014 at 19:15

> Counter is 32 bit,

OK so you have say ARR = 100 and counter CNT counting up, and when CNT = 90 you set ARR to 50. When do you think the next update/reload happens?

JW

anze2 · ‎2014-12-10

Posted on December 10, 2014 at 22:49

🙂 at approx. 4 billion micro seconds :):)

Ok, so every time i change arr, i must also set counter to 0. Sounds logical, i feel stupid i didn't remember this before. I'll let you know how this works, tomorrow will give it a try.

Thanks!

Anže

anze2 · ‎2014-12-11

Posted on December 11, 2014 at 16:14

Every time i changed ARR, i also reset counter to 0, so now it finally works!

Thanks guys!