Weird/Not fully understood behaviour of HRTIM

ambrose · ‎2015-07-07

Posted on July 07, 2015 at 13:26

Iam having big problems with the high resolution timer on the STM32f334microcontroller.

I am using a period of 0xD3C2, this would normally mean that writting 0xD3C2 to a compare register is full duty cycle (or zero - actually 0x60, as I am running at 4GHz - depending on the polarity). -

(I use compare registers one and two for two separate circuits).

And that the duty cycle will reduce progressively as you reduce the number. But this is not the case. what I have observed is that

0xD3C2 to a compare register is full duty cycle, but the behaviour of the hardware is unpredictable between a value of 0xD3C2 and 0xD3A2(ish).

Also, it seems that the act of writing to the compare register creates unusual spikes in the controlled circuits. I do know that the reference manual

specifies minimum and maximum values for compare registers depending on the CKPSC[2:0] values. I guess that these values are not

necessarily fixed, but depends on the actual period of PWM.

I am not sure exactly why it behaves odd, but could any one please enlighten me on this.

(I am running the PWM at about 85kHz)

Thanks.

#stm32f334 #hrtim

Amel NASRI · ‎2015-07-09

Posted on July 09, 2015 at 12:04

Hi,

Did you have a look to the HRTIM CookBook (

http://www.st.com/web/en/resource/technical/document/application_note/DM00121475.pdf

)? It explains how to do in order to program the HRTIM and provides some samples for typical use cases.

-Mayla-

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ambrose · ‎2015-07-21

Posted on July 21, 2015 at 10:58

Thanks for the response. Yes I have. I find that simply avoiding 100% duty cycle will make it behave normally, I just wanted to know if anyone has similar experience and know a better way. The reference manual does not say anything about this.