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Saturn par questions or a new way to ...

Discussion in 'Saturn Dev' started by RockinB, May 7, 2002.

  1. RockinB

    RockinB Staff Member

    Hy!

    I'm having such a PC <-> Saturn connection with an PAR 4M plus and commslink cart and here my thoughts:

    What about flashing the cart with an own application, so that it starts right after turning the Saturn on, without having to insert a CD and thus without modding the Saturn? The main problem with this is:

    What if the flashing fails? Can it be flashed again? With anything of the same size like the original firmware?

    OK, the firmware might contain instructions only readable by the PAR hardware, but it must also contain sequences of Saturn code that is loaded into Saturn's main memory at startup. So what I mean is to just modify this portion of the firmware.

    The benefit would be the one mentioned above and another one would be the possibility to flash it with a program with a functionality like the demomenu known from Dreamcast. So you may be able to set up the CD-ROM properly with that program and just insert a CD-R and let it play without letting the Saturn evaluate the protection ring of commercial CD's.

    Another problem with that would be the proper initialization of the CD-ROM. It was discussed in the message boards some time ago, but I haven't tested the supplied code yet.

    OK! Now what do you think about it? Can the problems be solved?

    By the way: Does anyone know something about the cartridge port specification and functionality. Any information would help.

    Rockin'-B
     
  2. ExCyber

    ExCyber Staff Member

    I see no reason that doing this wouldn't work. You wouldn't be able to load stuff from CD, though.

    Then you're left with a partially empty block of Flash wherever the flash process got derailed

    Yes. Unless you include a commslink program loader in your replacement code, though, you'd have to write a CD-based one. I might be able to help with this if you want to do it. Obviously, if the flash process fails at a point that leaves the cart-based commslink code loading procedures corrupt, you won't be able to use it to reflash.

    As far as I'm aware, yes. You don't get a great deal of space, though; the AR carts I've seen are only 256KB.

    Not likely. The PAR carts don't have any chips that can actually execute code.

    If this was possible, the Hong Kong AR clones would have something like it already. The CD reader won't function properly until the ring is checked. I had an idea to get around this just for homebrew stuff, but it would be a bit difficult and I'm not sure that it's even possible.

    According to the various docs I've read, the cartridge port sits on the so-called "A" bus of the Saturn. This is a 16-bit bus that connects the System Control Unit (the thing that handles memory mapping, interrupt control, DMA, etc.) to a couple other parts of the Saturn system (not sure, but I think the SCSP, CD interface, and SMPC sit on the A-bus). There's also an independent "B" bus hanldling other parts of the system. The cartridge port exists at multiple address ranges in the SCU mapping; there is a dedicated chip select signal that corresponds to each address range, so that it's possible to connect multiple memories without needing to add address decoding hardware to the cartridge (it would be a 50 cent part, but whatever [​IMG]). The SCU also seems to provide CAS/RAS signals for controlling and refreshing DRAM, though it's not clear to me that the cartridge slot also provides a corresponding multiplexed address bus; my EMS Action Replay 4M Plus uses multiplexers to generate the DRAM address from the flat address bus, but a multiplexed address bus seems like a pretty natural addition considering the huge number of pins and the fact that they bothered including multiple CS signals and CAS/RAS signals. I suspect that there's an SH-2 serial port on the cartridge interface as well, due to the pin layout of the Netlink cartridge.
     
  3. RockinB

    RockinB Staff Member

    OK, if nobody knows an answer, I'll have to do it for myself ??? .

    No, it will not be possible to load games from a CD-R with an application flashed on a PAR cardridge.

    And if the PAR can be flashed with any resident(into the firmware...) Saturn program I cannot say. I thought to ask if anyone ever tried this or if someone knows what happens then before I destroy my PAR with that.

    OK, bye

    Rockin'-B
     
  4. antime

    antime Extra Hard Mid Boss

    If a developer boot-disc existed, I'd imagine you could do the same with a resident program. I also recall reading (can't remember where, though) that a program running in cart space could control the CD system directly.
     
  5. TakaIsSilly

    TakaIsSilly New Member

    No, the problem is that the _initialization_ of the CD, the code that reads the ring, is in some place on the Saturn board, and defenitively not in the Saturn ROM (if you are up to saturn emulation, you'll notice that there's a allways a part when they say "the ROM seems to be waiting for something to continue", and "waiting" is a closed loop waiting for an interrupt). The Saturn dev "boot disk", has also such a ring, and that's how it works... it seems that we can change a few aspects of CD-ROM, after it is initialized. The PsyQ dev kit has something about it, mas was it correctly documented?
     

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