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Sonic 1 with Redbook Audio

Discussion in 'Engineering & Reverse Engineering' started by theocas, Dec 4, 2011.

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  1. Dec 6, 2011 #21
    LazloPsylus

    LazloPsylus

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    Finally fixed the hardware issues. Should work pretty damn close to perfect now on hardware.

    Many thanks to Flygon for pointing this out and helping us debug and bearing with us on Skype while we ripped out code and rewrote portions and rapidly tossed around test ROMs.
     
  2. Dec 6, 2011 #22
    Flygon

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    You guys are so epically awesome!!

    They are just so... AWESOME.

    I have wanted to see this sort of thing happen ever since I thought of the possibilities of Mode 1 being used... I really do have so many high hopes for this. :)
     
  3. Dec 6, 2011 #23
    Blastfrog

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    How easy would it be to add PCM support? It'd be cool to try to get it to run module music off the cart, if somehow possible.

    As a side note, I wonder how easily this could be combined with the 32x port of Sonic 1? It would be pretty neat to have the capabilities of both the Sega CD and 32x as a CD-32x game.
     
  4. Dec 6, 2011 #24
    theocas

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    PCM Support is all on the Sub-CPU, so it shouldn't be too hard now that we got the thing working on real hardware. There's just little documentation on the PCM chip that is available and tells us how to work the chip.

    The cart is already using Mode 1 of the Sega CD - it shouldn't be much harder adding 32X support also. Maybe we'll do that someday...
     
  5. Dec 6, 2011 #25
    Blastfrog

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    Maybe the PCM part of the Sonic CD sound driver could be ripped and used.
     
  6. Dec 6, 2011 #26
    theocas

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    That's true, but I don't think anyone's figured out where the driver lives and where it's stored on the Sonic CD disc. The PCM chip shouldn't be that hard to figure out though, it's just how Sega implemented it that's annoying.
     
  7. Dec 6, 2011 #27
    Blastfrog

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    I think Stealth has, if I'm not mistaken. How well do you think the Sega CD would handle XM playback (with a limited number of channels, of course)?
     
  8. Dec 6, 2011 #28
    theocas

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    I think the Sega CD could easily handle 8 channels with panning and volume control, if that's all the Sub-CPU in the SCD is doing. A nice ~12 MHz 68k with plenty of RAM and a CD drive. I'm working on a MD tracker anyways and was planning to use the Sega CD for 8 more PCM channels when connected. OH MY GOD YOU HEARD TOO MUCH ASDFG
     
  9. Dec 6, 2011 #29
    Falk

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    this + this yes plz
     
  10. Dec 7, 2011 #30
    theocas

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    You have the ability to make that happen =P Just check the first post. You can just make a new CD with the track layout mentioned there.
     
  11. Dec 7, 2011 #31
    Falk

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    Sorry, could I have a step by step tutorial on how to burn a CD?
     
  12. Dec 7, 2011 #32
    Blastfrog

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    Just load the disc image into an image burning software, select the drive you have a blank CD in, burn at the lowest possible speed (the higher the speed it's burned at, the less likely the Sega CD can read it, 10x or so at max). Maybe use something like ImgBurn, works well enough for me, very simple and easy to use.
     
  13. Dec 7, 2011 #33
    Flygon

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    Actually, I recommend setting ImgBurn to MAX (not AWS, MAX) instead of the lowest possible speed. Provided you don't bump your CD drive, the margin of error isn't too great anyway.

    Take it from someone that's had more failures in form of 1x burn speeds than MAX burn speeds. ;)
     
  14. Dec 7, 2011 #34
    Sik

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    Because besides the fact doing that in itself is a huge change to the core engine... there's also the fact you need to rewrite pretty much all hardware access. Not to mention the Z80 can't access MCD hardware, so for games that use SMPS/Z80 you will have to replace the sound engine. And I'm still not talking about taking advantage of the MCD hardware (besides loading), but just using the MD-side hardware. As soon as you start dealing with the MCD hardware it becomes madness in terms of porting.

    Also I don't get from where the 256KB number comes, considering MCD's work RAM is 512KB.
     
  15. Dec 7, 2011 #35
    Flygon

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    From what I gather, apparently 256KB of the 512KB work RAM is reserved by the hardware for some reason. I'd say more, but I'm kinda dumb and just relaying stuff I've heard from other people. :v:
     
  16. Dec 7, 2011 #36
    theocas

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    That number comes from the Word RAM size - which I'm pretty sure is often used by Sega CD games to hold the MD-side code. The Sub-CPU has it's own 512KB Program RAM, but about 128KB or even more are reserved by the BIOS and the system as disk buffers, etc.

    It's usually just simpler to use those 256K of Word RAM instead of trying to squeeze it all into program RAM.

    The issue is this - you need to have all of your art for the zone, including for example, character artwork, as well as basically the entire game engine and code to load your next chunk of code for the next zone or the special stage or some shit like that. The pointers shouldn't be all that hard if you know how to properly use your assembler. tl;dr: The Sega CD hardware is 'a huge b-word to work with,' as Fygon put it that one time on Skype.
     
  17. Dec 7, 2011 #37
    Shadow Hog

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    Ah, so is that why Sonic CD has its unusual jumping noise? I had been wondering.

    Doesn't really explain why Chaotix also went with it, since I'm pretty sure I heard Z80 use in the music (the Z80's where the square wave/noise channels come from, correct?), but eh.
     
  18. Dec 7, 2011 #38
    theocas

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    I doubt that's why Sonic CD has that jumping noise, as I believe it still uses the FM channel, Sega just decided to be a little odd about it. The Z80 can still be running and access the MD hardware, it just won't have access to the MCD hardware. Usually, most CD games just use the Z80 for sound effects, and the CD-DA or PCM for the actual music.

    The Z80 doesn't generate the square wave and noise channels, those come from the SN76489 in the VDP. The 32X however has some PWM channels that I believe Chaotix uses for some things.
     
  19. Dec 7, 2011 #39
    ICEknight

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    I was wondering, does this "mode 1" allow to read data from the Mega-CD?

    If it does, perhaps it would be possible to make it play the Sonic CD intro and ending, even? That would rule.
     
  20. Dec 7, 2011 #40
    Puto

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    If they wanted to have the normal jump sound effect in Sonic CD, they would. Changing the sound effect was a deliberate decision, there is absolutely no limitation whatsoever about using the PSG in the Mega CD.
     
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