topic Problem in Systick timer on KL46Z in Kinetis Microcontrollers

Problem in Systick timer on KL46Z

duyba — Thu, 09 Oct 2014 15:35:28 GMT

Hi all,

I am the beginner and I am having problem in blinking 2 Leds with distinct frequencies (1 Hz, and 2 Hz). How can I config Systick_config() function to get 2 different frequencies at the same time?

Thank you!

P/s: sorry for my bad English.

Re: Problem in Systick timer on KL46Z

mjbcswitzerland — Thu, 09 Oct 2014 17:07:31 GMT

SysTick can only generate interrupts at a single periodic rate.

It also has a maximum rate so it is often not possible to directly generate 1Hz (50MHz clock will, for example, allow about max. 335ms period).

To control multiple periods you can use a fixed TICK speed (say 50ms) and then a SW counter for each period that you would them like to control something.

eg.

Each time the SysTick interrupt fires (assumed 50ms rate)

static int iTimer1 = 0;

static int iTimer2 = 0;

if (++iTimer1 >= (500/50)) {

iTimer1 = 0;

TOGGLE_LED1(); // toggle LED 1 at 1Hz

}

if (++iTimer2 >= (250/50)) {

iTimer2 = 0;

TOGGLE_LED2(); // toggle LED2 at 2Hz

}

Regards

Mark

http://www.utasker.com/kinetis.html

Re: Problem in Systick timer on KL46Z

duyba — Thu, 09 Oct 2014 17:34:33 GMT

Thanks for your advice. The variables: Timer1 and Timer2 will increase whenever SysTick interrupt? So we still need to define the SysTick configuration by function SysTick_Config() in main section? Could you explain more about this function such the function's parameter? I think we can directly generate 1 Hz by SysTick_Config(SystemCoreClock/1), the clock of System is 48 MHz. Thanks!

Regards,

Duy

Re: Problem in Systick timer on KL46Z

mjbcswitzerland — Thu, 09 Oct 2014 18:53:18 GMT

Duy

I don't know the function SysTick_Config() so you will need to look at its code to see what it does any what its parameters control.

Beware that the SYSTICK reload register has only 24 valid bits and so the largest value that can be set is 0x00ffffff, which is about 349.5ms with 48MHz core clock.

Regards

Mark

Re: Problem in Systick timer on KL46Z

duyba — Fri, 10 Oct 2014 00:02:55 GMT

Thanks so much for your help!

Regards,

Duy