Colibri VF50 CPU frequency

What is the working frequency of Colibri VF50 CPU? Uboot writes this while booting:
CPU: Freescale Vybrid VF500 at 396 MHz
Is this 396MHz fixed or it can be adjusted by linux as described in ?

We are currently working on EMC measurements so we woud like to understand possible sources of HF disturbaces generated by Colibri module. We have found one peak aproximately at 450MHz in Radiated Emissions (Electric field) measurements, which we are not able to identify where is this comming from. Do you have any suggestion what part of Colibri module can generate this 450MHz peak?

The Colibri VF50 CPU is running at 396MHz, and on Vybrid based modules this is fixed (note that the article you mentioned does not have the “Applicable for” Colibri VF50 tag…).

It is not common that one observes CPU frequency in EMC measurements as this is a purely internal clock. Typically one can see frequencies of external peripherals, and quite often harmonics thereof (2nd/3rd/… harmonic of a certain frequency). There is the display root clock which is at 450MHz, but that is not brought out, so I doubt it is the display clock. To make sure it is not the display you can disable/remove the DCU node in the device tree (see Device Tree Customization). Furthermore you can have a look at all the clocks using sysfs:

cat /sys/kernel/debug/clk/clk_summary

To isolate the issue you can try disabling external peripherals or try chainging their operating frequency. Once you know what peripheral is causing the issue, you can try tweaking the pin configuration, especially the speed and drive strength property (see the Pinmux chapter in the Device Tree Customization article).

Dear Stefan,

thank you for nice explanation. We will follow your recommendation.