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# Handy - RetroBIOS

Type | libretro
Classification | community_fork
Source | https://github.com/libretro/libretro-handy
Upstream | https://handy.sourceforge.net/
Version | 0.95
Profiled | 2026-03-23
Cores | handy
Systems | atari-lynx

Technical notes

Handy is an Atari Lynx emulator by K. Wilkins (Handy 0.95, 2007). The core loads lynxboot.img from the system directory and validates it by CRC32 (0x0D973C9D). If the file is missing or the CRC does not match, the core falls back to an internal HLE BIOS that replicates the boot sequence in software (ram clear, cart loader decrypt, jump to $0200).

The HLE path intercepts CPU calls to ROM addresses FE00, FE19, FE4A and FF80 via a Mikie register write trap (address 0xFD97). When useEmu is true (no valid BIOS loaded), CRom initialises mRomData with a default fill byte (0x88) plus reset vectors pointing to the HLE entry points.

Upstream Handy 0.95 requires the BIOS (throws CLynxException) and validates by checking the first 16 bytes against a hardcoded signature. The libretro port added the HLE fallback and switched to full CRC32 validation.

For headerless cartridges (no LNX/BS93 header), the core loads howard.o from the system directory. This is the Epyx development kit bootloader used to bootstrap raw/headerless ROMs into memory. Upstream requires howard.o for headerless carts (throws exception); the libretro port makes it optional (logs error, continues).

2 files | 0 required, 2 optional | 1 in repo, 1 missing | 1 with HLE fallback

`lynxboot.img` -optional, HLE available : Atari Lynx boot ROM (Mikie internal 512B ROM)

- System: atari-lynx
- Size: 512 B
- CRC32: `0d973c9d`
- Validation: size, crc32
- Source: `rom.h:48-49 (ROM_SIZE=0x200, ROM_CRC32=0x0D973C9D), rom.cpp:76-129 (CRom constructor), libretro.cpp:1231-1258 (bios path + CSystem init)`
- Platforms: batocera, lakka, recalbox, retroarch, retrobat, retrodeck, retropie
- Validated by CRC32 at load time. If invalid or missing, core uses HLE fallback (system.cpp:303-361 HLE_BIOS_* functions, system.cpp:406-428 trap writes).

`howard.o` -optional, missing from repo : Epyx Howard bootloader for headerless cartridges

- System: atari-lynx
- Source: `system.cpp:197-238 (CartHeaderLess check, howard.o load via fill_pathname_resolve_relative)`
- Loaded only for headerless carts (no LNX/BS93 header). Resolved relative to the BIOS file path (system directory). Passed to CRam for execution. Most commercial games have headers and skip this entirely.

Generated on 2026-03-25T14:56:43Z