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Reverse-engineering and analysis of SanDisk High Endurance microSDXC card (2020)

As seen on Hackaday! TL;DR – The SanDisk High Endurance cards use SanDisk/Toshiba 3D TLC Flash. It took way, way more work than it should have to figure this out (thanks for nothing, SanDisk!…

Many manufacturers break out the Flash’s data bus onto hidden (and nearly completely undocumented) test pads, which some other memory card and USB drive manufacturers take advantage of to make cheap storage products using failed parts; the controller can simply be electrically disabled and the Flash is then used as if it were a regular chip. By sniffing the data bus at the DSLogic’s maximum speed (and using its 32 MB onboard buffer RAM), I was able to get a clear snapshot of the commands being sent to the NAND Flash from the controller during initialization. When looking at the logic analyzer data, I noticed that the controller sends the READ ID command twice, but the first time it does so without resetting the Flash (which should normally be done as soon as the chip is powered up!).

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