Clarification on sdmmc3 data lines

[darsan.pradeep]

what we are doing:
We are using a nano SOM on our custom carrier board.
We have used the default settings provided by Nvidea , by that I mean we used jetpack 4.6.2 with L4T 32.7.2 with Jetson Nano Pinmux.
The chip is being flashed for jetson nano devkit emmc.

My Queries:

1. whether after enabling SD card in dtsi file (tegra210-porg-p3448-common.dtsi) for sdmmc3 , if i check all data lines of external SD card whether it will always be 1v8 even while reading and writing also sd card clock.
2. whether any of clock or data lines may go above 1v8 , like while booting up.

[Trumany]

Hi, please refer to the SD protocol for answers. SD port design on nano follows the protocol and so the voltage level on lines.

[darsan.pradeep]

@Trumany

SD protocol for answers

I am assuming by SD Protocol/SD port design you are referring to either to
Chapter 9. SD Card and SDIO in “NVIDIA Jetson Nano
Product Design Guide”
or
section 4.5 in “Jetson Nano System-on-Module
Maxwell GPU + ARM Cortex-A57 + 4GB LPDDR4 + 16GB eMMC”

so by checking the the pinmux sheet and dts and dtsi , files if I am only nabing sd card in dtsi “tegra210-porg-p3448-common.dtsi”

sdhci@700b0400 {
                status = "okay";
                /delete-property/ keep-power-in-suspend;
                /delete-property/ non-removable;
                mmc-ddr-1_8v;
                mmc-ocr-mask = <3>;
                uhs-mask = <0x0>;
                tap-delay = <3>;
                       };

I should be getting 1v8 in all data lines right, that is where i wanted your guidance and clarification for assurance that our custom hardware is not effecting voltage to 3v3

[Trumany]

I mean SD specifications as below. If you read the specs you will find both 3.3v and 1.8v are necessary.

[darsan.pradeep]

thank you, I understand what you meant.
I believe a small miscommunication has happened as I hadn’t told my purpose.

We are trying to implement a eMMC instead of external sd card with our SOM with eMMC , thus our product will be having 2 eMMC’s.
This is a case in continuation of “External eMMC support for Jetson Nano”

we had been told to try it , it seems possible as seen from case “How to flash the OS to external eMMC”

since eMMC can’t handle more than 1v8 ,we are trying to make sure clocks and data lines of sdmmc3 doesn’t exceed 1v8.
from the cases, I have checked it seems possible with software configurations and no hardware changes.

That is why to my previous question
if in pinmux sheet the voltage is set to 1v8.
no other changes except enabling sd card.

now after flashing data lines and clock of sdmmc3 , shouldnt it still be 1v8 according to what i read, or still there is a chance of voltage to go to 3v3 that can damage eMMC.

[Trumany]

External eMMC is not supported. There are no more info can be shared than below content as you read in other topic.

"That was not validated. If you insist using that, then you can copy the sdmmc4 device tree and see if it can work.

However, we cannot guarantee it would work."