SD Card on Jetson Nano Emmc 16gb

I have flashed our EMMC module using the instructions located here:
It has successfully flashed the EMMC and I have a question
EMMC does not detect an external SD slot or the presence of an SD Card so how to fix it?

The background on the topic is that on eMMC models all of the equivalent of what a BIOS would provide (Jetsons don’t have a BIOS) goes into partitions, along with boot content. On the purely SD card models (dev kits; third party modules are all eMMC) this equivalent to BIOS plus boot goes into QSPI memory directly on the module. The particularly important part is that for SD card models the SD card mount is directly on the module, and on eMMC models, if the third party vendor has provided an SD card slot, it goes on the carrier board itself (not the module).

To support non-plug-n-play hardware which cannot self-report what and where it is the device tree is used. This means third party vendors of any carrier board which is not an exact match to the reference carrier board will provide their own board support package (BSP) for flashing. Quite often it is just a device tree patch to the original NVIDIA flash software, or a repackaged version of the same.

During boot the bootloader content is not part of Linux. The boot content could be considered its own micro operating system. It’s only purpose is to overwrite itself with something else, but what it has in common is that it needs drivers for any hardware to be used in that stage. This includes the ability to find that hardware, which in turn usually means the device tree plus driver.

The default software for any non-SD card model of Jetson expects eMMC, and does not include drivers or software to find the SD card slot. That’s up to the third party vendor since it is their software. On some occasions the vendor will state that the NVIDIA software is used directly, which implies their carrier board is an exact match to the electrical layout and features of the NVIDIA carrier board.

If the SD card is not detected while in Linux, then it implies you don’t have the right device tree (possibly also a driver, but this is almost always just a device tree issue; does the vendor provide a device tree or flash software which you did not use?). If the SD card is being used during boot, then it implies you need the third party vendor to provide the method of making the SD card slot visible at boot stages.

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