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dynamic frequency change

Posted by beppe r on November 27, 2009
Hi all,
in a cortexM3 (stm32) project i am using FreeRTOS and i need to change dynamically core frequency (min being 8Mhz and max 72Mhz, default 16Mhz).

in an old post Richard Barry suggested the following:
*In Source\portable\MPLAB\PIC32MX\port.c you will see the function vPortIncrementTick(). This calls vTaskIncrementTick() just once. If you have the frequency, change this so vTaskIncrementTick is called twice. If you quarter the frequency, change this so it is called 4 times. Etc.*

i was wondering if i can instead change the systick interrupt config when i change core freq.


RE: dynamic frequency change

Posted by Richard on November 27, 2009
Not sure exactly what you are asking - but you have to ensure that time moves at the same speed for the kernel. If you slow down the core speed by 2, then assuming this causes the tick interrupt occurs at half the frequency, you will have to call vTaskIncrementTick() twice in each tick interrupt.


RE: dynamic frequency change

Posted by Richard Damon on November 27, 2009
Richard, I believe that he is asking if you cut the clock speed in half, and also cut the clock cycles per tic interrupt in half (so the tics still happen at the same rate) with that work, and I think it should. It will increase the overhead by the tic interrupt, but that is sort of to be expected.

RE: dynamic frequency change

Posted by Richard on November 27, 2009
Richard_damon, I agree with you.


RE: dynamic frequency change

Posted by beppe r on November 28, 2009
exactly what was i looking for :)

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