Michael Chuah

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6 years, 7 months ago.

Actual clock speed is only 120MHz instead of 180MHz?

When I print the following line, I see that the system clock is only 120MHz instead of 180MHz. Is there some setting I need to change to increase the clock speed?

Code used to print SystemCoreClock

printf("SystemCoreClock = %d MHz\r\n", SystemCoreClock/1000000);

Question relating to:

Last updated: 27 Aug 2020
The FRDM-K66F is a low cost development platform for Kinetis® K66, K65, and K26 MCUs.

120MHz is the setting in Normal Run mode. 180MHz is available in HSRUN mode.

posted by Mahesh Mahadevan 15 Sep 2017

1 Answer

Jenny Plunkett
6 years, 7 months ago.

Hi Michael,

The answers on this question may help: https://os.mbed.com/questions/78259/System-clock/

I tried out your printf statement on my own K66F, and I am also showing 120 MHz. However, if I add the code below to my main function (before the printf statement), I now see the SystemCoreClock as 160 MHz. 

SystemCoreClockUpdate();

The code above is found in the following file: /mbed-os/targets/TARGET_Freescale/TARGET_MCUXpresso_MCUS/TARGET_K66F/device/system_MK66F18.c

Let me know if you have any questions!

- Jenny, team Mbed

Accepted Answer

Update: Mahesh's comment above looks correct according to this file: https://github.com/ARMmbed/mbed-os/blob/master/targets/TARGET_Freescale/TARGET_MCUXpresso_MCUS/TARGET_K66F/TARGET_FRDM/fsl_clock_config.c#L137

posted by Jenny Plunkett 15 Sep 2017