High Hopes

In a world of magnets and miracles:

Theia v1

It’s internal codename is Phoebe but I’m probably going to name the final product Theia. And in case you’re still confused – it’s a 21-pin ODE for SEGA Saturn.

It’s not perfect though – you won’t be able to play CD+G discs. Well, audio will play but that’s it. Shouldn’t be a problem as those discs are rare and proper dumps even more so, but it’s a pity as I was able to get it working on Rhea. On the bright side I did get as close as possible with it and the results are very promising for PCE, which uses a very similar subcode protocol.

Before you start asking – it’s not for sale yet. There are several variants of the 21-pin drive and the device must be first tested with each one. That’ll take time.

35 thoughts on “High Hopes

  1. good news~!
    btw, I didn’t even know that any SEGA Saturn games are CD+G format..?! I thought it is just Karaoke CD..

  2. So, are you not able to display graphics of a CD+G but play only music or unable to boot a CD+G?As far as I know graphics information of a CD+G are is in 6 bits of data.

    • The problem is getting Saturn to recognize those 6 bits when you push them out🙂
      And no, it does not affect booting.

    • Excuse me, Deunan, but how these 6 bit differs from other data bus signals?Frequency, lenght, amplitude?

      • It’s 8 bits because (in general) you don’t send PQ and R-W subs separately. The problem is getting all clock signals in sync, which – if done purely in software – requires high speed interrupts. Not a great idea. External logic on the other hand would complicate things.
        Well, I’m still considering few more ideas.

  3. OK, thanks for explanation.I know for sure there are slight hardware differences between 20 and 21PIN Saturn but I’m wondering why this issue has appeared only on the latter .
    Did you consider hardware modification on Saturn motherboard, too?

    • Data/audio stream is nearly identical on both drive models, but subcode output is completly different. You don’t really need that for games though.

    • OK, Deunan.But I’m speaking more from a point of view of an engineer like you, taking this a as personal challenge more than from gamer perspective.I’m sure you understood what I mean🙂

  4. How are you tracking down units to test with. It’s my understanding that it’s near impossible to know what drive is in a system without opening it. Have you figured out a way to easily identify systems or have you just been asking around to find the different models?

  5. Model 1 Saturns with the oval Buttons and the plexiglass on the front edge are USUALLY 20 pin. I think theres 1 revision thats 21 pin. you have much more of a chance of getting a 20 pin if you buy one with oval buttons.

    Model 2 Saturns with the round buttons are all 21 pin.

    • I’ve bought the last month jest to be prepared. In the meanwhile I’ve rgb modded it😀

  6. well done deunan,im happy for the guys with their 21p saturns.
    and great that pce is going in the good direction.
    keep up the good work.

  7. Wicked!
    I’m already on the list for a Rhea, but this would be great for my other Saturn (one for Ram cart games, one for memory cart).
    I will be watching with much interest.

      • About the port not being able to go beyond x2 for data… Out of curiosity… Could a firmware hack unlock this restriction? Or are they hardware bottleneck issues? Saturn hardware is a schizophrenic mess with many processors so i guess it would fall apart trying to play with firmware or CD controller (VDP2?) ;)… Anyway i don’t remember of terrible loading times, so no big deal.🙂

        Should we expect same limits on PC Engine? Or Interface Unit with ODE attached could be pushed faster than x1? Is CDrom2 exactly the same as PC8801MC CDrom unit? Which is a SCSI-1 device if i remember correctly so in theory it can reach 5MB/second..? x2 would already be awesome though

        Thank you🙂

      • Drive bitstream is clocked exactly for x2 speed, you can’t have more unless you replace or bypass the whole CD block (SH1+ASIC) with your own hardware. Which is possible on some Saturns but would be way more expensive. The MPEG-slot ODE has the potential to be faster but time will tell just how much, there’s going to be another roadblock somewhere. The two SH2’s are not exactly speed demons and doing plenty of other things. The biggest issue isn’t even the CPU speed but the fact that both access the same bus so fight all the time for the memory cycles. Making the DMA from CD block any faster will actually cause even more stalls on the main CPUs…

        PCE is x1 by default but yes, ODE can be quite faster. But then it’s a 8/16 bit system, with puny main clock, I wouldn’t be surprised if the main CPU simply couldn’t process the data any faster anyway.

  8. Hi everybody. I m french so sorry for my poor english. I want to buy gdemu but i don t know how to send you a mail cause i can’t see your email adress. Can we still buy gdemu ? I just discovered it and… I need it it s unbelievable. Please answer me.
    Thank you bye bye

  9. This is a fantastic announcement. the vast majority of my systems are 21 pin based. I’m half tempted to switch my request to this instead of Rhea. I’ve got to have at least 10 different systems, including the dreaded PC-Trap version.

  10. Deunan are you planning to do The Sega Cd model 2 first? It seems the logical one because its a flip top and has plenty of room inside for an Ode.

    Sega cd model 1 would need some re-thinking on the hardware to work with it since its a front loader.

    Any plans to ever make one for the Jvc x eye? I may be wrong but i think it uses the same drive as the Later model 2 units. I know it uses the same pickup Optima 6s.

  11. Hi, I’m having a problem with my Dreamcast that I have GDEMU installed in. Earlier today, my Dreamcast crashed and since then, when I turn it on. It seems to get stuck at the Dreamcast logo screen. Have you seen or heard about this happening? I’m not sure if it’s related to GDEMU but I figured you’re pretty intimately familiar with the hardware so you’d be a good person to ask.

    • Update: after a minute or so it gets to the BIOS and just says “Please wait while disc is being checked.”

      • I have had the same problem with my GDEMU modded Dreamcast since yesterday. It restarted a few minutes into a game and since then it haven’t been working properly. Sometimes it gets stuck on the logo, sometimes it boots into the BIOS menu with distorted sounds, and other times it gets stuck on the “checking disc-screen”. I thought it might be my Dreamcast that was broken, but with is old GD-rom drive reinstalled it seems to work fine.

  12. Excellent news!!!! I will definitely get one when it is available! Currently have a 21pin mod chip, but this will be much easier.

  13. I had once seen a list of the various models of Saturns and which type of drive was usually found in them.. I’ll have to see if I can find it again.

  14. Three things:
    1. Great!
    2. I do not receive your posts via email… Hmmm
    3. Have you ever thought about doing the same for PSX? You’ll surely rock.

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