System Disk 2 little secret

Discussion in 'Sega Dreamcast Development and Research' started by MetalliC, Feb 1, 2019.

  1. MetalliC

    MetalliC Spirited Member

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    Hi. can't find information about this secret anywhere so posting here...

    Normally this disk boots to screen with single "Complete" word and waiting for disk change.
    but if plug controller into port D and hold Y button while booting you'll get this:
    dcsysdisk2_0.png
    which gives few more options. last option validate inserted disk and provide various information:
    dcsysdisk2_1.png dcsysdisk2_2.png dcsysdisk2_3.png
     
  2. -=FamilyGuy=-

    -=FamilyGuy=- Site Supporter 2049

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    Nice find! Very interesting!
     
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  3. wombat

    wombat SEGA!

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    Awesome find! Never heard about this trick before, so it was definitely a great kept secret. I guess this finally gives the .CDI that is normally useless a little bit more functionality :)
     
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  4. Anthony817

    Anthony817 Familiar Face

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    Wow this is very cool!
     
  5. -=FamilyGuy=-

    -=FamilyGuy=- Site Supporter 2049

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    That'd be nice to try. It wouldn't work on a GD-R OFC, but it should be able to read info from GD-Rom. Might be interesting to see what it does to a mil-cd.
     
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  6. darcagn

    darcagn Site Supporter 2013, Site Supporter 2014

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    Really cool! Not that useful, but interesting nonetheless. I have never heard of this and I own an SD2 and know several others that do.
     
  7. fafadou

    fafadou Enthusiastic Member

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    Very interesting :)
     
  8. Borman

    Borman Digital Games Curator

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    I remember seeing this ages ago, but long forgot it and as you said, its basically gone from the Internet. Thanks for that reminder, fun to basically re-learn something like this :)
     
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  9. PrOfUnD Darkness

    PrOfUnD Darkness Familiar Face

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    Amazing find.
     
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  10. MetalliC

    MetalliC Spirited Member

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    agree, I can only imagine it may be useful as an IP.BIN viewer - boot from SD2, insert some GD-R(s) and check if their's texts/dates match final games or already dumped prototypes (at "SYSTEM ID" and "Binary code" screens you may press up/down to scroll and view more information).

    there is also one more, mostly unknown, usage of SD2 - for NAOMI 1/2 GD-R booting. if insert System Disc 2 into NAOMI GD-drive you'll see screen like this:
    dcsysdisk2_4.png
    then you may change disc to some NAOMI-GD game written on GD-R and it will be run.
     
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  11. fafadou

    fafadou Enthusiastic Member

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    There is some naomi GD-R or I misunderstood ? For me, the naomi games are only in the naomi board...
     
  12. MetalliC

    MetalliC Spirited Member

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    @fafadou NAOMI games was ROM cartridges, then DIMM board (kind of RAM cartridge with GD-drive) + games on GD-ROMs. and later, in ~mid 2000s, when GD-ROM manufacture was closed Sega switched back to flash ROM cartridge media.

    during game development for NAOMI + DIMM/GD-ROM system, at it's final stage developers must be sure GD disc image was built right and works ok, before submitting it to mass manufacture at least.
    and System Disc 2 (together with some code in DIMM firmware) provide such possibility - devs burn game to GD-R disc and then boot it using SD2 to check if everything works as it should.
     
  13. PrOfUnD Darkness

    PrOfUnD Darkness Familiar Face

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    That's amazing, so Naomi recognizes the Dreamcast system disk (I'm not sure why I'm surprised but cool nonetheless). What happens if you try a Dreamcast GD-R though?
     
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  14. wombat

    wombat SEGA!

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    This is so obvious, yet I never thought of trying it. Thanks for bringing this to our attention.

    Using a burned Dreamcast GD-R with NAOMI data should work in that case. Fun fact, NAOMI GD-R's have mainly been ripped using a stock Dreamcast with httpdack.
     
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  15. darcagn

    darcagn Site Supporter 2013, Site Supporter 2014

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    It's not that surprising when you consider that the DC System Disk does not actually run code on the DC to unlock booting GD-Rs (you can put the disc in and take it right back out without launching it and GD-Rs will work). It's done by the disc drive. The disc drive firmware recognizes the System Disk and disables its security ring protection. So it's really a disc for GD-ROM drives, not for Dreamcasts or NAOMIs.
     
  16. Laurent

    Laurent Spirited Member

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    Woaw nice found.

    I never try combo button for disc system 2.

    Hum i try combo button whit the checkers disc I have ...
     
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  17. MetalliC

    MetalliC Spirited Member

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    actually, it was the cause why I put an eye on System Disk 2 - to do a bit of research about this protection.
    where "put an eye" means disassemble, analyze, trace etc usual RE things. not stupid and useless guessing ;)
    if you think drive does security check on it's own - no, it don't made in this way. Dreamcast BIOS/syscalls (or DIMM firmware) send to GD-drive 2x special commands - 1st perform security check (ATAPI command x70), and 2nd (ATAPI command 0x71) returns check result - big chunk of garbage-looking data with obfuscated result code. there is also Katana Dev.box BIOS-es, which doesn't send 2 these commands.
    anyway, Dreamcast BIOS does this security check in any case - if it was regular GD-ROM game, or if it was System Disc 2 which was replaced with some game GD-R.
    so, how the magic works ? I'm not 100% sure, sadly there is no clear evidences.
    my current theory is - if there was inserted GD-ROM disc and was performed security check commands - GD-drive will remember that, and all subsequent "security check" commands will return "OK" result, until GD-drive reset, even if disc was swapped with GD-R.
    also possible, as you said - there is special magic markers on SD2, which does the same as described above (switch drive to "check always OK" state), but IMO it is less probable.

    iirc I've posted already research results ? - "checker" discs may be switched to various interesting "run modes" using special controller device, which uses a bit special maple device reply format, not the same as Dreamcast controller.
    so, no, you can't do anything interesting with it using regular controller.
     
  18. -=FamilyGuy=-

    -=FamilyGuy=- Site Supporter 2049

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    AFAIU, it is the wobble of the sd2 that's peculiar and causes the magic to happen. The actual sd2 program doesn't participate in any way, it's eye-candy/red-herring/bonus.
     

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