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# Flycast - RetroBIOS

Type | standalone + libretro
Classification | official_port
Source | https://github.com/libretro/flycast
Upstream | https://github.com/flyinghead/flycast
Version | 0.1
Profiled | 2026-03-23
Cores | flycast
Systems | sega-dreamcast, sega-naomi, sega-naomi2, sega-atomiswave

Platform details

dreamcast: - bios_size: 2097152 - flash_size: 131072 - ram_size: 16777216 - hle_available: True - source_ref: core/nullDC.cpp:333-345 naomi: - bios_size: 2097152 - sram_size: 32768 - ram_size: 33554432 - hle_available: False - source_ref: core/nullDC.cpp:346-354 naomi2: - bios_size: 2097152 - sram_size: 32768 - ram_size: 33554432 - hle_available: False - note: Treated as NAOMI in the libretro port. Separate platform only in upstream. - source_ref: core/nullDC.cpp:355-363 atomiswave: - bios_size: 131072 - sram_size: 131072 - ram_size: 16777216 - hle_available: False - source_ref: core/nullDC.cpp:364-375

Technical notes

Flycast has a built-in HLE BIOS (reios) for Dreamcast that can boot most games without real BIOS files. Arcade systems (NAOMI, Atomiswave) require MAME-format BIOS ROM archives.

The libretro port (libretro/flycast, last updated 2025-12-12) is significantly behind upstream (flyinghead/flycast). Key divergences: - NAOMI 2 has no separate BIOS entry or platform detection; NAOMI 2 games run as NAOMI using naomi.zip. Upstream has naomi2.zip with dedicated ROMs. - System SP is not supported. Upstream has segasp.zip support. - The n2_ prefix for NAOMI 2 flat boot ROMs is dead code (DC_PLATFORM_NAOMI2 is never assigned to settings.System in the libretro port). - Flash search includes legacy names (%flash_wb.bin, %flash.bin, %flash.bin.bin) that upstream has removed. - NAOMI flat boot ROM search includes epr-21576d.bin fallback not in upstream.

BIOS file search uses prefix + name pattern. The libretro port appends "dc/" to the system directory (libretro.cpp:1866). All files below are relative to system_dir/dc/.

The prefix is determined by platform (sb_mem.cpp:32-49): Dreamcast -> dc_ Dev Unit -> hkt_ NAOMI -> naomi_ Atomiswave -> (no prefix, BIOS loaded from awbios.zip)

Boot ROM search pattern (sb_mem.cpp:51-68): {prefix}boot.bin, {prefix}boot.bin.bin, {prefix}bios.bin, {prefix}bios.bin.bin NAOMI also tries: epr-21576d.bin (sb_mem.cpp:59) Flash/NVRAM search pattern (sb_mem.cpp:231): {prefix}nvmem.bin, {prefix}flash_wb.bin, {prefix}flash.bin, {prefix}flash.bin.bin

11 files | 2 required, 9 optional | 10 in repo, 1 missing | 2 with HLE fallback

`dc_boot.bin` -optional, HLE available

- Path: `dc/dc_boot.bin`
- System: sega-dreamcast
- Size: 2.0 MB
- Aliases: `dc_bios.bin`, `dc_boot.bin.bin`, `dc_bios.bin.bin`
- Source: `core/hw/holly/sb_mem.cpp:219,55-57`
- Platforms: batocera, emudeck, lakka, recalbox, retroarch, retrobat, retrodeck, retropie
- Dreamcast boot ROM. HLE BIOS (reios) used as fallback. Code searches prefix + boot.bin, boot.bin.bin, bios.bin, bios.bin.bin sequentially.

`dc_nvmem.bin` -optional, HLE available

- Path: `dc/dc_nvmem.bin`
- System: sega-dreamcast
- Size: 128.0 KB
- Aliases: `dc_flash_wb.bin`, `dc_flash.bin`, `dc_flash.bin.bin`
- Source: `core/hw/holly/sb_mem.cpp:231,196-213`
- Dreamcast flash memory / NVRAM. Created if not found. Code searches prefix + nvmem.bin, flash_wb.bin, flash.bin, flash.bin.bin sequentially.

`font.bin` -optional, missing from repo

- Path: `dc/font.bin`
- System: sega-dreamcast
- Source: `core/reios/reios.cpp:736-754`
- Dreamcast system font for HLE BIOS text rendering. Built-in font used as fallback.

`naomi_boot.bin` -optional

- Path: `dc/naomi_boot.bin`
- System: sega-naomi
- Size: 2.0 MB
- Aliases: `naomi_bios.bin`, `naomi_boot.bin.bin`, `naomi_bios.bin.bin`, `epr-21576d.bin`
- Source: `core/hw/holly/sb_mem.cpp:219,58-59`
- Platforms: retrodeck
- NAOMI boot ROM (flat binary). Alternative to naomi.zip. epr-21576d.bin is searched without prefix.

`naomi.zip` -required

- Path: `dc/naomi.zip`
- System: sega-naomi
- Source: `core/hw/naomi/naomi_roms.h:133-188`
- Platforms: batocera, emudeck, lakka, recalbox, retroarch, retrobat, retrodeck, retropie
- NAOMI system BIOS archive (MAME format). Contains region-specific BIOS ROMs: epr-21576h.ic27 (Japan), epr-21577h.ic27 (USA), epr-21578h.ic27 (Export), epr-21579d.ic27 (Korea). Also used for NAOMI 2 games in the libretro port (no separate naomi2.zip).

`airlbios.zip` -optional

- Path: `dc/airlbios.zip`
- System: sega-naomi
- Source: `core/hw/naomi/naomi_roms.h:78-85`
- Platforms: lakka, recalbox, retroarch, retrodeck, retropie
- Airline Pilots Deluxe BIOS. epr-21802.ic27 (Export), epr-21801.ic27 (USA).

`f355bios.zip` -optional

- Path: `dc/f355bios.zip`
- System: sega-naomi
- Source: `core/hw/naomi/naomi_roms.h:96-103`
- Platforms: lakka, retroarch, retrodeck, retropie
- Ferrari F355 Challenge BIOS. Japan/USA/Export variants.

`f355dlx.zip` -optional

- Path: `dc/f355dlx.zip`
- System: sega-naomi
- Source: `core/hw/naomi/naomi_roms.h:105-119`
- Platforms: lakka, retroarch, retrodeck, retropie
- Ferrari F355 Challenge Deluxe BIOS. Japan/USA/Export variants.

`hod2bios.zip` -optional

- Path: `dc/hod2bios.zip`
- System: sega-naomi
- Source: `core/hw/naomi/naomi_roms.h:121-131`
- Platforms: lakka, recalbox, retroarch, retrodeck, retropie
- House of the Dead 2 BIOS. Japan/USA/Export variants.

`naomigd.zip` -optional

- Path: `dc/naomigd.zip`
- System: sega-naomi
- Source: `core/hw/naomi/naomi_roms.h:190-212`
- Platforms: recalbox, retrodeck
- NAOMI GD-ROM BIOS. Shares ROMs with naomi.zip (epr-21576h, epr-21578h, epr-21577h).

`awbios.zip` -required

- Path: `dc/awbios.zip`
- System: sega-atomiswave
- Source: `core/hw/naomi/naomi_roms.h:87-94`
- Platforms: batocera, lakka, recalbox, retroarch, retrobat, retrodeck, retropie
- Atomiswave system BIOS archive (MAME format). Contains bios0.ic23 (Sammy, 128 KB).

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