boot is a built-in sysmodule.
Boot
First, it initializes gpios and sets the gpio voltage to 1.8v.
Then it checks battery charge and SoC temperature using i2c. If either is bad, it shows one of two different bitmaps from .data in the framebuffer.
Because most sysmodules have not yet booted, this all uses raw IO pokes when it comes to gpio and i2c interfacing.
Otherwise, it continues by reading the bad_block_table.num_entries field from the BCT located at offset 0x00C000 in the NAND boot partition 0 (safe mode backup).
If bad_block_table.num_entries byte0 is non-zero, it does a repair with type=4. If byte1 is non-zero, it does a repair with type=5. The number of entires in the bad block table should always be 0x200 by default (represents partition_size). Values from 0x200 to 0x20F represent bad blocks in the NAND boot partition 0 while values from 0x210 to 0x21F represent bad blocks in NAND boot partition 1.
Repair
It uses the NCM IContentMetaDatabase Iterate command with the supplied type value in order to look up the firmware package ("bip") title-id (0100000000000819 or 010000000000081A).
It then mounts the firmware package at "bip" and reads the BCT from the "bip:/nx/bct" file in that filesystem. Afterwards, the console's keyblob is read from the NAND keyblob array using bootloader0_info.version as index and the selected keyblob is then injected into the BCT's customer_data region.
A SHA-256 hash is then calculated over this new BCT and compared against calculated hashes of the actual BCTs stored in NAND. For a type4 repair process, the comparison is performed with "normal" and "normal backup" BCTs (offsets 0x0000 and 0x8000 in NAND). For a type5 repair process, the comparison is performed with "safe mode" and "safe mode backup" BCTs (offsets 0x4000 and 0xC000 in NAND). If either hash doesn't match the calculated one, it returns error 0xC9E.
The same process is repeated for the package1 file in "bip:/nx/package1". This file's SHA-256 hash is compared against calculated hashes over the package1 copy stored in NAND. For a type4 repair process, the comparison is performed with "normal" and "normal backup" package1 (offsets 0x100000 and 0x140000 in NAND boot partition 0). For a type5 repair process, the comparison is performed with "safe mode" and "safe mode backup" package1 (offsets 0x00000 and 0x40000 in NAND boot partition 1). If either hash doesn't match the calculated one, it returns error 0xC9E.
Finally, the process is repeated once more for the "bip:/nx/package2". Error 0xC9E is returned in case of mismatch.
If this function returns 0xC9E, it calls a function to repair the NAND.
Done
When done it calls the pm:shell NotifyBootCompleted (which launches boot2), and exits itself.
Changelog
2.0.0
- All panic strings were removed/censored.
- Code to initialize gpio differently for Copper/Icosa (based on spl HardwareType flag) was removed.
- The "WecDriver" now uses svcReadWriteRegister instead of svcQueryIoMapping to write to 0x7000E400 MMIO (PMC).
2.1.0
- Code was updated with changes to the NCM interface.