Overview

This is the file format for the 3DS' Firmware, it contains four 'sections' of ARM code (ARM9 and ARM11). The firmware sections are not encrypted in the FIRM format.


A structural example of a FIRM file (created using the specs in ctrtool) can be found here (Note does not contain ARM code, it's just a structural example)

FIRM Header

OFFSET SIZE DESCRIPTION
0x000 4 Magic 'FIRM'
0x004 4 Reserved1
0x008 4 ARM11 Entrypoint
0x00C 4 ARM9 Entrypoint
0x010 0x030 Reserved2
0x040 0x0C0 (0x030*4) Firmware Section Headers
0x100 0x100 RSA-2048 signature of the FIRM header, using SHA-256.

Firmware Section Headers

OFFSET SIZE DESCRIPTION
0x000 4 Offset
0x004 4 Address
0x008 4 Size
0x00C 4 Firmware Type ('0'=ARM9/'1'=ARM11)
0x010 0x020 SHA-256 Hash of Firmware Section