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Flycast - RetroBIOS
Type standalone + libretro
Classification Official ports
Source https://github.com/libretro/flycast
Upstream https://github.com/flyinghead/flycast
Version 0.1
Profiled 2026-03-23
Cores flycast, flycast_dev, flycastvl
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 | 11 in repo, 0 missing | 2 with HLE fallback

dc_boot.bin optional in repo HLE fallback

dc_nvmem.bin optional in repo HLE fallback

  • 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 in 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 in repo

  • 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, romm
  • NAOMI boot ROM (flat binary). Alternative to naomi.zip. epr-21576d.bin is searched without prefix.

naomi.zip required in repo

  • 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, romm
  • 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 in repo

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

f355bios.zip optional in repo

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

f355dlx.zip optional in repo

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

hod2bios.zip optional in repo

naomigd.zip optional in repo

  • 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 in repo

Generated on 2026-04-18T08:05:07Z