STM32L0x2 timer frequency off by 10%

[Fiskk]

Hello!

I'm trying to setup up timer6, i need to use it at different frequencies at different times. To test the timer i toggle an output pin in the ISR and measure the frequency with an oscilloscope, but the frequency is consistently off by about 10%.

Any suggestions to why this is? My solution would be to multiply the wanted frequency by some calibration factor.

I would like a frequency of 2 Hz, so the timer interrupts should be at 4 Hz to toggle on and off.

The timer setup is:
32 MHz PLLCLK
Prescaler = 125
Period = 64000

[Tesla DeLorean · Accepted solution]

Use N-1 values to divide by N

124 to divide by 125

63999 for divide by 64000

[Fiskk]

Of course, thanks!
Now it's is off by 0.5 % but i guess that's because of the error tolerance of the clock=?

[TDK]

0.5% is within the tolerance of the internal HSI, if that's what you're using as a clock. A crystal will provide a much more accurate clock, to tens of ppm or so. The HSI can also be trimmed, but is not going to be stable long term or across temperatures.