How does the eMMC hidden partition work?

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How does the eMMC hidden partition work?

Unread post by callmesteve » Sat Aug 11, 2018 6:30 am

I am struggling to understand how the eMMC boot partition behaves with flashing an image to the eMMC.

Apparently, for one, there is no way to modify the hidden partitions (or they are always read-only; I am not sure) from any device that does not natively use the eMMC, such as a normal Linux computer. Is this a flaw of the MicroSD adapter system or the HK-brand reader? What makes the Odroid able to access and modify this when a PC can't? Has anyone found a way to do so?

With this inability to modify, how does flashing work? I guess it uses a normal image, complete with the boot area, but that one gets ignored in favor of the one in the hidden area, and its only problem is that this flashed one wastes a few K of space?

Lastly, how does Fastboot work if using that to update? I couldn't ask that in the original topic on card readers, since it was offtopic, but how would one use Fastboot to modify any of these? I know that the Android eMMC flasher image seems to use it, so it can be run from the device itself? (and is the normal use of it from the host PC or the Odroid? A lot of guides make it ambiguous how or where that command is run from.)
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Re: How does the eMMC hidden partition work?

Unread post by odroid » Mon Aug 13, 2018 9:41 am

If your PC has a native eMMC interface via PCIe bus, you can access it probably.
Otherwise, you have to access(read/write) the hidden boot block on the XU4 board because PC standard USB mass-storage protocol doesn't support the eMMC hidden boot block.

The fastboot works in u-boot software with a totally different protocol from the USB mass-storage.
But it needs a micro-USB port which is not available in XU4 board.

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