Why does the manual specify UnTXD/UnRXD/UnRTS/UnCTS as being muxable from GPIO17 to SD_DATA_1?

[Icefirejm]

Hello all!

According to page 48 of the datasheet, UART should be muxable to any GPIO pin. However, on page 70, it's specified that that UART UnTXD/UnRXD/UnRTS/UnCTS goes to a specified range of pins, as shown below.

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Maybe I am looking too much into this, but if UART can go on any GPIO, why is it specified to these pins? I thought at first it might have to do with the fact that these pins are not specified as GPIO (except GPIO 17 is included in the matrix), but according to page 15, these pins are GPIO too:

21e5371de9f574bfc669511623f4eb30.png (112.69 KiB) Viewed 8203 times

Also, considering these pins can be muxed to any GPIO, does that mean these pins belong to any power domain they are muxed to? I can also not find a clear explanation of this.

Thank you for reading!

[Sprite]

They are both muxable using the GPIO matrix (to any GPIO) or the IOMUX (to some designated pins). The difference is that the path to the IOMUX is more direct, which means lower and generally more predictable latency as the signal doesn't have to travel to the GPIO matrix first. You could make the point that UARTs generally aren't that sensitive to latency to begin with and you would be right; I think the decision of also allowing them to be routed via the IOMUX mostly is a historical thing.

In general, the pins themselves are connected to a power domain; which signal you route to it (either using the IOMUX or the GPIO matrix) doesn't matter.

[Icefirejm]

Ah, that makes perfect sense and helps a lot. Thank you so much for your concise response!