GPIO pins with alt function GPCLK are incorrect

[V3lectronics]

According to the cm5 datasheet https://datasheets.raspberrypi.com/cm5/cm5-datasheet.pdf (section 2.6.1)

pins with the GPCLK alt function are: GPIO4, 5, 6, 18, 20, 21. Imo the easiest way to see them is with ctrl + F.

However I am a little confused because the datasheet also says that there are only 2x GPCLK pins available...

My guess is that some of the pins are mapped to the same clock of the SoC. E.g. both GPCLK[1] pins are mapped to the same clock.

Thank you for maintaining this project it has been very helpful to me!

[atctwo]

Hello!

Your guess is correct, as far as I understand. Each peripheral might have more than one GPIO pin the signal can be mapped to. In the datasheet, at the end of section 2.6 it recommends that you only have each signal mapped to one pin at a time:

Each GPIO can have one function selected at a time. Likewise, each peripheral input (e.g. I2C3_SCL) should only be
selected on one GPIO at a time. If the same peripheral input is connected to multiple GPIOs, the peripheral sees the
logical OR of these GPIO inputs

It is confusing that the datasheet says there are two GPCLKs. There seem to actually be three GPCLK controllers ([0], [1]. and [2]), each of which can be mapped to a couple of different GPIO pins.

I think it says that there are two GPCLKs since GPCLK[1] is apparently reserved for system use. I don't think it mentions it in the datasheet but the pigpio documentation suggests this.

This RPi Forums post suggests that GPCLK[1] is used for the Ethernet and USB controllers, but since those are managed by the RP1 on the Pi 5 / CM5 I'm not entirely sure if GPCLK[1] really is reserved on the Pi 5. If you really need GPCLK[1] then I would experiment a bit with different frequencies just to make sure it won't crash the Pi!

I hope is helpful, and I'm glad you found the project useful!