MegaCD BIOS automatically goes to CD player screen after 10 seconds

[adimifus]

I can't recall exactly when this started happening, but when I start the MegaCD core and leave it on the BIOS screen, it will automatically go to the CD player after approximately 10 seconds and freeze there. This ONLY happens with US and EU model 1 BIOS-- Japanese model 1 and all model 2 BIOS behave normally.

This wasn't always the case. The MegaCD core used to sit at the BIOS animation until you hit START whether a game was loaded or not, like real hardware.

[neogeo81]

Then just use model 2 bios...

[Chris23235]

I can't recall exactly when this started happening, but when I start the MegaCD core and leave it on the BIOS screen, it will automatically go to the CD player after approximately 10 seconds and freeze there. This ONLY happens with US and EU model 1 BIOS-- Japanese model 1 and all model 2 BIOS behave normally.

This wasn't always the case. The MegaCD core used to sit at the BIOS animation until you hit START whether a game was loaded or not, like real hardware.

I can confirm this, but I am not sure if it is not the intended behavior, it looks, like the MegaCD Bios is not able to detect a disc properly at this moment and goes to the CD-Player because it assumes to have a Audio CD but crashes, because there is none. Can you verify what happens on real hardware with a machine equipped with Bios 1 (the version I tried was 1.1).
If you can confirm this you should open an issue at Github:
https://github.com/MiSTer-devel/MegaCD_MiSTer/issues

Then just use model 2 bios...

Not helpful

[adimifus]

Can you verify what happens on real hardware with a machine equipped with Bios 1 (the version I tried was 1.1).

I have a Model 1 Sega CD (BIOS v1.1), and it will sit at the animated SEGA / SEGA CD screen indefinitely whether a game is in the drive or not. A game won't actually start until you press the START button after loading the disc. Speaking of which, I forgot to mention the MegaCD core will also automatically start the game rather than waiting for START to be pressed.

If you can confirm this you should open an issue at Github:
https://github.com/MiSTer-devel/MegaCD_MiSTer/issues

I wanted to check here first to see if others had similar problems and if I was possibly doing something wrong.

[rhester72]

I'm starting to get the impression that folks are confusing hacked BIOSes with legitimate ones. There are indeed hacked ones with that very 'feature' (to auto start), but at least official US v2.00 does not.

I'm going to test all of the real ones to see what the behavior is.

[rhester72]

The plot thickens.

Of all 28 official BIOS versions here: https://segaretro.org/Sega_Mega-CD/Boot_ROM

only three exhibit the auto start behavior:

96ea588d647f2ab1f291279fc691663c [BIOS] Sega CD (USA) (v1.00).md
SEGA MEGA DRIVE (C)SEGA 1992.JULSEGA-CD BOOT ROM08/04-1992 03:00 1.00 SEGA-CD BOOT ROM BR 000003-1.00

e66fa1dc5820d254611fdcdba0662372 eu_mcd1_921027.bin
SEGA MEGA DRIVE (C)SEGA 1992.OCTMEGA-CD BOOT ROM10/27-1992 15:15 1.00 MEGA-CD BOOT ROM BR 000004-1.00

2efd74e3232ff260e371b99f84024f7f us_scd1_921011.bin
SEGA MEGA DRIVE (C)SEGA 1992.OCTSEGA-CD BOOT ROM10/11-1992 18:30 1.10 SEGA-CD BOOT ROM BR 000003-1.10

Most interestingly, while these are all indeed SCD1 variants, the Japanese versions of same do NOT exhibit the behavior, so it's limited to the US and EU CD1 versions only.

I'm next going to test these on a different emulator to see if the behavior changes.

[rhester72]

Wow, that was disappointing. Of EVERY emulator on Zophar's, the only one that a) works on Windows 11 and b) lets you boot the BIOS without a CD inserted is Kega Fusion. That being said, it does not exhibit the problem, so I'd concur pretty conclusively now this is a legitimate bug in the core indeed (but quite mystifying!).

[adimifus]

The plot thickens.

Of all 28 official BIOS versions here: https://segaretro.org/Sega_Mega-CD/Boot_ROM

only three exhibit the auto start behavior:

96ea588d647f2ab1f291279fc691663c [BIOS] Sega CD (USA) (v1.00).md
SEGA MEGA DRIVE (C)SEGA 1992.JULSEGA-CD BOOT ROM08/04-1992 03:00 1.00 SEGA-CD BOOT ROM BR 000003-1.00

e66fa1dc5820d254611fdcdba0662372 eu_mcd1_921027.bin
SEGA MEGA DRIVE (C)SEGA 1992.OCTMEGA-CD BOOT ROM10/27-1992 15:15 1.00 MEGA-CD BOOT ROM BR 000004-1.00

2efd74e3232ff260e371b99f84024f7f us_scd1_921011.bin
SEGA MEGA DRIVE (C)SEGA 1992.OCTSEGA-CD BOOT ROM10/11-1992 18:30 1.10 SEGA-CD BOOT ROM BR 000003-1.10

Most interestingly, while these are all indeed SCD1 variants, the Japanese versions of same do NOT exhibit the behavior, so it's limited to the US and EU CD1 versions only.

This is the same results I got. Thanks for confirming this. I submitted an issue on GitHub.

[CaldWanderer]

Has anyone tried other emulators besides Kega Fusion to see if the same issue occurs there?

[rhester72]

Has anyone tried other emulators besides Kega Fusion to see if the same issue occurs there?

Good luck finding one that runs on Windows 11 64-bit. I was going to try RetroArch but couldn't be bothered.

[FPGA64]

Has anyone tried other emulators besides Kega Fusion to see if the same issue occurs there?

Good luck finding one that runs on Windows 11 64-bit. I was going to try RetroArch but couldn't be bothered.

what about

https://ares-emu.net/compatibility/sega ... ?status=-1

Ares supports the Mega Cd

[rhester72]

I'll take a look.

[rhester72]

Just tried Ares.

Confusingly,

Code: Select all

SEGA MEGA DRIVE (C)SEGA 1993.JUN
CD2 BOOT ROM     06/01-1993     20:00      2.00W
14db9657bbaa6fbb9249752424dc0ce4  boot.rom

DOES autostart on Ares (with seemingly no way to disable this behavior) but not on MiSTer.

We're gonna need real hardware.