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# JAXE - RetroBIOS

Type | libretro
Classification | official_port
Source | https://github.com/kurtjd/jaxe
Version | GIT
Profiled | 2026-03-24
Cores | jaxe
Systems | chip8

Platform details

bios_mapping: - target: none - source_ref: jaxe_libretro.info:17, src/chip8.c:118-168 - notes: All font/sprite data is compiled into the binary. The standard

CHIP-8 hex font (5 bytes per character, 16 characters) and the SCHIP big hex font (10 bytes per character, 16 characters) are stored as a static array in chip8_load_font() and copied into RAM on every reset. No file I/O is performed for BIOS or fonts.

Technical notes

JAXE is a CHIP-8, SCHIP, and XO-CHIP emulator by Kurtis Dinelle, ported to libretro. Supports .ch8, .sc8, .xo8, and .hc8 ROMs.

No external BIOS or font files required. The core has firmware_count = 0 in jaxe_libretro.info and never calls RETRO_ENVIRONMENT_GET_SYSTEM_DIR.

Font data is hardcoded in chip8_load_font() at src/chip8.c:118-168. The standard 4x5 hex font (0-F, 80 bytes) is loaded at address 0x000, and the SCHIP 8x10 big hex font (0-F, 160 bytes) follows immediately after at address 0x050. Both are written directly into chip8->RAM[] during chip8_reset() -> chip8_load_font().

Memory layout from include/chip8.h:42-45: 0x000-0x04F standard font (NUM_FONT_BYTES = 80) 0x050-0x0EF big font (NUM_BIG_FONT_BYTES = 160) 0x0F0-0x0FF stack (STACK_SIZE = 16) 0x100-0x10F audio buffer (AUDIO_BUF_SIZE = 16) 0x200+ program ROM (PC_START_ADDR_DEFAULT)

The fonts/dbgfont.ttf file in the repo is only used by the standalone build (src/main.c:19) for the SDL debugger overlay, not by the libretro core.

No BIOS or firmware files required. Generated on 2026-03-25T14:56:43Z