Forced to Run Core Clock at Half Speed

[derekschumacher]

Using processor expert, I am trying to set up the microcontroller to run off of an external clock source. I think we have the processor expert settings mostly figured out, but for reasons that are unclear to me, we can't run the core clock at the MCG output frequency.

We are using the MK22F256VLL12. Here is the working configuration (note core clock speed of 56 MHz):

And here is the non-working configuration (note core clock speed of 112 MHz):

According to this image from the manual, it really seems like we should be able to run the core clock at the MCGOUTCLK frequency.

Is this an error in processor expert? Or have I neglected to do something important with the configuration? Or am I  just misunderstanding how the MCG works?

[mjbcswitzerland · Accepted solution]

Derek

If you are using the K22FN256 you may need to configure the high speed run mode (maybe at a different location in the tool?).

In the normal RUN mode the maximum specified core/system speeds are 80MHz and the bus clock needs to be <= 50MHz.

Flash can be <= 26.667 MHz.

If you configure high speed mode of operation you can then work at the full 120MHz core/system speed but you won't be able to program or erase flash in this mode.

Below are the optimal configurations for the K22FN256 in the two modes as shown by the FRDM-K22F running in the uTasker simulator:

RUN mode

High-Speed RUN mode.

Regards

Mark

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

K22: http://www.utasker.com/kinetis/FRDM-K22F.html / http://www.utasker.com/kinetis/TWR-K22F120M.html

For the complete "out-of-the-box" Kinetis experience and faster time to market

:smileyinfo: Out-of-the-box support for 46 Kinetis boards and 10 IDEs (460 combinations from a single code source with no porting required)

[derekschumacher]

I'm surprised I was able to run with the 56 MHz bus speed since that violates the <= 50 MHz rule in normal run mode. Anywho you are absolutely correct, I needed to allow high speed run modes from the CPU component:

[mjbcswitzerland]

Derek

Actually I have had no problems (in the lab) running the K22FNxxx at 120MHz core and 60MHz bus, and programming Flash (in normal RUN mode).

In HS-RUN Flash operations will return errors (and there are a few other chip restrictions).

It is however not recommended to use these settings out-of-spec. in (real) products, although they probably will work (under normal conditions).

I have seen various 'products' based on the Teensy 3.2 (72MHz K20) using 96MHz core clock. Some people obviously don't really care and find it exciting to live dangerously and over-clock their products....

Regards

Mark

[derekschumacher]

Just to clarify, am I ok to run in high speed mode during operation, as long as I am within the spec for high-speed operation?

You're recommendation is just to program in normal-speed operation yes?

[mjbcswitzerland]

Derek

These are the HSRUN mode restritions. Otherwise you can use stay in that mode and use the full speed of the device.

Regards

Mark