Timer 3 clock half of that expected

[Chris Tams]

Posted on June 05, 2018 at 11:27

Hi, we are struggling to understand the behaviour of the timer clock for the STM32F767zi.

We are using the nucleo-F767zi board, at 216MHz.

The  for APB1 prescalar is 4, and due to the x2, we are 

expecting the Timer3 clock to be 108MHz

.

All of our tests so far are showing the timer clock is 54MHz, the same as APB1.

For example to get a 1mS timer, I need to use a timer prescalar of 53 and a period of 999, whereas  I am expecting to use 107 and 999.

This is the same behaviour using the example cube code and our own.

Has anyone seen this behaviour or can suggest anything please ?

[Chris Tams]

Posted on June 05, 2018 at 12:32

[Chris Tams]

Posted on June 05, 2018 at 12:33

I had incorrectly considered the Gpio pin output as the clock frequency.

The interrupts being generated are indeed the correct frequency when using the cube code.