CCM_CLKO1 Giving Clock Signal at Reset

[hamzaatifi]

Hi,

We are using CCM_CLKO1 as a GPIO in our application, but we’re seeing a clock signal output at reset, which is not ideal for our setup. This behavior is shown in the attached oscilloscope screenshots.

Details:

• Environment: The measurement was taken in SD card boot mode with and without the SD card inserted.
• Observation: CCM_CLKO1 (and CCM_CLKO2) gives a clock output at reset, even though we intend to use CCM_CLKO1 as a GPIO.
• Potential Cause: This seems to occur earlier in the boot process and cannot be caused by our software (U-Boot/Kernel). We suspect it might be related to the boot flow, possibly the ROM loader.
• Concern: This clock signal is problematic for our application, and we would like to know if this behavior is normal or if there’s a way to disable the clock output at reset so we can use CCM_CLKO1 as a GPIO without interference.

Any insights or recommendations on how to resolve this would be greatly appreciated!

Thank you!

[JorgeCas · Accepted solution]

Hello,

This is an expected behavior since reset state will change IOMUX register to configure the pin as CCM_CLKOX function and is changed until device tree is loaded.

As you mention, U-boot/kernel does not causes this.

If you change the IOMUX option before e.g. in SLP, you could reduce the time with the clock output at reset.

Best regards.