Dreamcast Would a Mini GD be possible on a CDROM?

[Pitito]

From what I have been able to investigate, a GDROM is basically a CD, except for the central ring and it has greater capacity, but the latter can be done by software, some time ago plextor recorders were created using a technology called GIGAREC, they could be recorded up to 120 min on 100 min cds, something very similar to GDROM technology.
Also from the checks made I have the theory that a GDROM is burned with a single session in mode 1, while the formula that we have been using during these years has always been 2 sessions in mode 2.

With this I have prepared to create a minigd, although I know that it would not start due to the protections, I wanted to see its behavior on the console.

I have created an iso LBA 45000, and passed to bin, cutting it into 3 tracks and using the first 2 tracks of the original GDI.
Then I created a CUE adjusting the times of each track to match the LBA of the tracks. One .CUE for a 2 session image and one for a one session image

And this is the behavior in console.
2 session image
BURN MODE1 2352
It takes about 20 seconds to try to access the data, but in the end you can hear the verification sound as if it were an original.



A single session
BURN MODE1 2352
Quickly access the data and the verification sound is heard as in the originals, but it no longer goes from there


This makes me think that maybe MINI GDS can be created, if the protections are removed either by IP.BIN or by means of MOD BIOS.
Today there is more knowledge about the machine than 20 years ago and great modders such as @megavolt85, @yzb, @japanese_cake, @SiZiOUS, etc... and that surely they could achieve it.

Just give thanks to @FamilyGuy, who has been guiding me to do these tests

 

[MetalliC]

Today there is more knowledge about the machine than 20 years ago

sorry to disappoint you, but there is still close to zero knowledge about physical GD-ROM media layout and protection checks performed by GD-drives. virtually no work or research was performed during 20 years, people was happily exploiting MilCD boot and that's all.

also I'd recommend to examine GD patent https://patents.google.com/patent/EP0935242A1/
it is way more complex than you thinking of it.

 

[Pitito]

Yes, in that I give you every reason, I always go for the easy thing (milcd), but in those years I think it was the most normal thing to exploit.
Today to great modders as I have commented, who know Dreamcast programming well, and perhaps by hacking bios or ip.bin it could be possible to create these types of images without the console verifying if it is original or not

 

[MetalliC]

Today to great modders as I have commented, who know Dreamcast programming well, and perhaps by hacking bios or ip.bin it could be possible to create these types of images without the console verifying if it is original or not

yes, it is possible to do BIOS mod which will boot software from "regular" CDs, not only multi-session XA (MilCD). but why ? most of Dreamcast owners these days more interested to use ODE and get rid of GDs or CDs medias at all.

 

[Pitito]

Yes, today many already have GDEMU or any other ODDE, but there are also still many people who prefer to use their GDROM unit in which I include myself, it may seem strange but many of us are still using our dear reader.

 

[MetalliC]

Yes, today many already have GDEMU or any other ODDE, but there are also still many people who prefer to use their GDROM unit in which I include myself, it may seem strange but many of us are still using our dear reader.

I'd say it in other way, there is people who:
1) likes to use Dreamcast "as is", with no hardware mods
2) prefer to use various hardware mods or addons if possible
obviously 1) is not interested to do/use BIOS ROM chip replacement, while 2) will prefer to use more handy drive replacement options (GDEMU, etc)

and in general, is there any practical benefits from you idea ? I see none

 

[Pitito]

Yes, I understand your position, for example I have dual bios, since it is something in which I keep the original bios, plus another modified bios, but in the case of the gdrom, I like to have the physical games with their respective covers.
In another Dreamcast I have SD with dremshell, which I have for testing ...
I also have two more spotless ones
Maybe for most people, this would have no benefit (maybe 10-15 years ago it did), due to ODDES, but it could be one more option for GDROM users.

I think something similar to the Bleemcast may happen, I think there is already a Bleemcast available for GDEMU, if I remember correctly it was @megavolt85 who did it, but this is something that @japanese_cake also wants to implement in his next bios

 

[MetalliC]

and still me main question - WHY ?
if mimic GD-ROM structure on regular CD-R you will just waste 10min of disc space (~100Mbyte), with no any benefits

 

[Pitito]

and still me main question - WHY ?
if mimic GD-ROM structure on regular CD-R you will just waste 10min of disc space (~100Mbyte), with no any benefits

Well, for me the most interesting thing would be to make those 0winceos games run well that do not do it in cdi
Maybe there is something else in other games

 

[MetalliC]

if speaking more seriously - recently I've examined a bit more "DC checkers" code, and located GD-drive firmware update routine, which does like:

• send packet command "FF 00 00 00 00 00 00 00 00 00 00 00" 3 times
• send packet command "CB 00 00 00 00 00 00 C0 00 00 00 00" followed by 2Kbyte firmware

sadly, firmware itself is missing, but potentially this open doors for clever soft-mods in future.

 

[deadlegion]

and still me main question - WHY ?
if mimic GD-ROM structure on regular CD-R you will just waste 10min of disc space (~100Mbyte), with no any benefits

Maybe to run CD-R backups on console with stock bios that doesn't support MIL-CD? idk


I have a Japanese VA1 with such a bios. It isn't a special edition VA2 (eg Sakura Taisen), just appears to be a fairly uncommon VA1 (plenty of people insist all VA1 boards are MIL-CD compatible). Installed GDEMU but it will only run GDI, so no unlicensed releases unfortunately.

Apparently (from what I've read) this console I have is a late Japanese VA1 board with different bios to prevent piracy (possibly same bios as VA2).

 

[Pitito]

If your console does not read MILCD, you can try data / data images, these images work in BIOS 2.1 (NOMILCD).
You can create this type of images with the pack of @FamilyGuy

But it could also be another option, since for games with audio tracks you would have to deal with it differently.

 

[deadlegion]

I tried some different data/data CDI but no CDI images work at all... well, at least I couldn't get any to work.
GDEMU won't even boot CDI menu I have to use GDI version.

 

[MetalliC]

@Pitito I'm sorry, but you barely understanding how this all these things works

in short: GD-drive does detect disc type, then BIOS read type value and chose: "normal GD" boot code path; or CD-XA code path (which may be dectected as MilCD after further checks); or do nothing for other disc types.
later BIOS revision doesn't do CD-XA code path, so no MilCD boot (technically almost all code is still there, but permanently disabled).

as of GD disc type detection - it is still absolutely unknown how it performed, some kind of dark magic inside of GD-drive firmware.
the only thing we know - after disc was detected as GD (-R or -ROM) retail Dreamcast's drive perform security ring check, and if it was failed (i.e. insert GD-R media with no/"empty" ring) - disc will not be accessible, at all.
Katana Dev.Box drives have different firmware, which have security ring check disabled, so they supports both GD-ROMs or GD-Rs.
also, sad to say, but this means: even if you'll cook some magic GD-like-CD which will be detected as GD by drive - you still fucked when it came to security ring check, it will fail and disc will not work if use regular Dreamcast drives.
BUT, it worth to try boot it in Katana dev box, there is slight chances such GD-like CDs will work.

 

[Pitito]

Man, I am not an expert on this subject, but I do have a slight idea of how it works.
I do not have any dreamcast with BIOS 2.1, but if I had read that if they load the images data/data, hence I have made him try, although I do not know if GDEMU is compatible with these images (Although maybe it's just rumors)
I have created quite a few releases in my dreamcast translations, and I remember that someone told me about a release that did not work for him in data/data, I no longer remember if he used GDEMU or another ODDE.

When I did these tests, from the beginning I knew that they would not start, I just wanted to see the behavior of dreamcast
I also know that for a GD to start, the requirements that you have mentioned must be met and some more such as that the executable bin must be from a certain sector (specifically 449850) otherwise the GD will not start.
As I say, I only know some basic things, but I also like to investigate these things