Flycast - RetroBIOS¶
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:1972). 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
BIOS[] also declares airlbios and naomigd. No entry of Games[] carries either name in its bios field and naomi_LoadBios is only ever called with that field or the literal naomi, so neither archive is opened. ref: naomi_cart.cpp:79,229-240,476-479, naomi_roms.h:79,191
9 files | 2 required, 7 optional | 9 in repo, 0 missing | 2 with HLE fallback
dc_boot.bin optional in repo HLE fallback
- 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,core/hw/holly/sb_mem.cpp:55-57 - Platforms: batocera, emudeck, lakka, recalbox, retroarch, retrobat, retrodeck, retropie, rocknix, romm
- 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 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,core/hw/holly/sb_mem.cpp: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:737-753 - 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,core/hw/holly/sb_mem.cpp:58-59 - Platforms: retrodeck, rocknix, 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).
f355bios.zip optional in repo
f355dlx.zip optional in repo
hod2bios.zip optional in repo
awbios.zip required in repo
Generated on 2026-09-14T09:03:09Z