About this reference

What is known about the X91’s stock firmware: formats, addresses and behaviour, as read from the dump and checked on the player. Addresses are those of the stock firmware (line 1.101.37) unless a page says otherwise; where a stage moved or replaced something, the page says so.

The predecessor’s SDK (US212A for the ATJ2127, partly published as PD196_ATJ2127) explains many names; the X91’s code matches it closely, with exceptions noted where they were found (the engine’s message numbers, for one).

Page	Covers
Hardware, boot and upgrade mode	identification, memory, boot record, upgrade mode, recovery
The firmware image (LFI)	the LFI container, its 137 files, CONFIG.BIN
Programs (.AP)	.AP layout, bank groups and their RAM, program ids, system calls, messages and keys
Resources, menus and fonts	.STY pictures, texts and layouts, list styles, .MCG menus, fonts, picture bookkeeping
Display driver (DRV_UI.DRV)	DRV_UI.DRV functions, keyed draws, list boxes and the counter, rotation
Shared interface code	status bar, app timers, list control, menus, key filter, screensaver
Music: program, engine and libraries	the music program, the engine and its messages, volume, the library builder, M3U.LIB
Other programs	main menu, settings, eBook reader, folder view, Bluetooth, programs never changed
Reading and writing the firmware	the vendor flash procedure on Linux, x91_flash.py, x91_tool.py