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adafruit / Adafruit_nRF52_Bootloader

USB-enabled bootloaders for the nRF52 BLE SoC chips
MIT License
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UF2: mismatched media types #51

Closed henrygab closed 5 years ago

henrygab commented 5 years ago

Issue:

From Microsoft FATGEN103.pdf: "Whatever is placed [in boot sector media descriptor] must also be put in the low byte of the FAT[0] entry"

From the UF2 exposed on a feather, using feather_nrf52840_express_bootloader-0.2.9_s140_6.1.1.hex:

Struct/Field Value Start Length Note
boot_sector.media_descriptor F8h 15h 1h Hard drive
boot_sector.drive_number 0h 24h 1h Corresponds to floppy
fat0.media_type FFF0h 200h 2h Floppy
fat1.media_type FFF0h 4200h 2h Floppy

Fix

PR request coming soon.

hathach commented 5 years ago

Thank you very much @henrygab , according to the above doc. MS-DOS v2 will only look at the BPB and skip the first byte in the FAT structure. But I agree they should match the other.

The determination of which type was on the disk was done by looking at the first byte of the FAT (the low 8 bits of FAT[0]). This type of media determination was superseded in MS-DOS version 2.x by putting a BPB in the boot sector, and the old style of media determination (done by looking at the first byte of the FAT) was no longer supported. All FAT volumes must have a BPB in the boot sector.

hathach commented 5 years ago

fix by PR #52