Allwinner NAND flashing
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A lot of Allwinner devices, especially the older ones (pre-H3 era),
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comes with a NAND. NANDs storages are a pretty weak choice when it
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comes to the reliability, and it comes with a number of flaws like
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read and write disturbs, data retention issues, bloks becoming
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unusable, etc.
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In order to mitigate that, various strategies have been found to be
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able to recover from those issues like ECC, hardware randomization,
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and of course, redundancy for the critical parts.
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This is obviously something that we will take into account when
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creating our images. However, the BROM will use a quite weird pattern
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when accessing the NAND, and will access only at most 4kB per page,
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which means that we also have to split that binary accross several
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pages.
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In order to accomodate that, we create a tool that will generate an
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SPL image that is ready to be programmed directly embedding the ECCs,
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randomized, and with the necessary bits needed to reduce the number of
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bitflips. The U-Boot build system, when configured for the NAND will
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also generate the image sunxi-spl-with-ecc.bin that will have been
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generated by that tool.
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In order to flash your U-Boot image onto a board, assuming that the
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board is in FEL mode, you'll need the sunxi-tools that you can find at
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this repository: https://github.com/linux-sunxi/sunxi-tools
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Then, you'll need to first load an SPL to initialise the RAM:
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sunxi-fel spl spl/sunxi-spl.bin
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Load the binaries we'll flash into RAM:
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sunxi-fel write 0x4a000000 u-boot-dtb.bin
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sunxi-fel write 0x43000000 spl/sunxi-spl-with-ecc.bin
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And execute U-Boot
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sunxi-fel exe 0x4a000000
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On your board, you'll now have all the needed binaries into RAM, so
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you only need to erase the NAND...
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nand erase.chip
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Then write the SPL and its backup:
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nand write.raw.noverify 0x43000000 0 40
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nand write.raw.noverify 0x43000000 0x400000 40
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And finally write the U-Boot binary:
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nand write 0x4a000000 0x800000 0xc0000
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You can now reboot and enjoy your NAND.
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