Keeping 2 Timer Interrupts with different Frequencies in Sync

[LMorr.3]

Hello,

I have two 32bit timers running on an STM32F373, TIM2 and TIM5.  

I have successfully chosen TIM2's prescale and ARR values to generate the 'update' interrupt as I require by using TIM2's prescale set to 0 and modifying the ARR to set  a target frequency.  TIM2 is working as I need.

I now need to have TIM5 run its interrupt the same way, but 24 times faster than TIM2.  If I change TIM2's ARR value, I plan on setting TIM5's ARR to TIM2->ARR/24.  

My question is; Over time, I see TIM5 will become slightly out of synch with TIM2 due to rounding.  Is it ok to adjust TIM5->CNT each time TIM2's interrupt occurs to ensure they are in sync?  Is there a better way to do this?  I was looking at cascading timers but maybe that is too complex compared to just setting TIM5->CNt on each TIM2 interrupt.

UPDATE:  I think I have this figured out.  I'll re-configure my setup a bit to make use of only 1 TIM running at 24x with a cnt variable to trigger a function instead of a second timer's interrupt. 

Thank you!!

[Sarra.S]

Hello @LMorr.3 

Any updates on this topic? 

[LMorr.3]

Hello,

I had added an 'update' note to my original post, so I'll all good now, thank you!!

[KnarfB]

Anyway. Note, that to divide a timer clock by x, you have to set ARR to x-1, not x. This might have caused the error you have observed.

hth

KnarfB

[MasterT]

I've solved similar task before, instead of divide by /24 you need multiply x24.  First set ARR value of the tim-5 -> fast, than ARR2 =  (ARR5 +1) x 24 - 1.