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Thread: Mega-CD/Sega CD FPGA Optical Disc Emulator

  1. #31
    Raging in the Streets Sik's Avatar
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    The power usage is a lot lower thanks to not having a physical CD drive in the first place :​P (and you missed a thread in the Genesis Does subforum)

    Quote Originally Posted by Gentlegamer View Post
    I didn't know CD game data can be accessed through the cart slot.
    Oversimplification but the expansion slot is pretty much similar to a second cartridge slot with some missing lines (kinda as it runs off a different address range and such, but cartridge slot gets the full address so it can snoop whatever it wants).

  2. #32
    SITE SUPERVILLAIN Outrunner Vector's Avatar
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    Quote Originally Posted by Sik View Post
    The power usage is a lot lower thanks to not having a physical CD drive in the first place :​P (and you missed a thread in the Genesis Does subforum)

    Oversimplification but the expansion slot is pretty much similar to a second cartridge slot with some missing lines (kinda as it runs off a different address range and such, but cartridge slot gets the full address so it can snoop whatever it wants).
    Been waiting 10 years for this =0
    Last edited by Vector; 07-08-2019 at 03:38 AM.
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  3. #33
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    Quote Originally Posted by Wesker View Post
    What interests me the most is the possibility of having Mega Drive games hacked with CD quality music tracks, just like the SD2SNES/MSU-1 does with the SNES.

    Oh yes, oh yes. This brings A LOT of new possibilities.
    Here’s one to get you started: Moonwalker

  4. #34
    Nameless One BRNexus7's Avatar
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    Quote Originally Posted by chilled View Post
    Dude I'm from Spain I didn't even recognize the accent. On Andorra for tax purposes, probably...
    Also this thing must feed 400 GB sd cards (on exFat!) what the hell.

    One more thing: does this actually overclock a stock Megadrive? Does this mean any stock MD rom loaded from the Mega SD will be run from the FPGA 68k 12 Mhz gpu? So all those FPS crippled games (racing, polygonal, etc.) would run at decent FPS? Or when loading a stock MD rom it will just load it to the stock CPU as the everdrive does? My guess is the latter
    You don't need a 400GB card. There are only 200 Sega CD games and most are duplicates. You'll only likely need a 400GB card down the road when there are a bunch of audio enhanced Genesis games for it.

    No, it doesn't overclock Genesis CPU. The Sega CD unit itself has its own 68K CPU clocked at 12.5Mhz, the MegaSD simply simulates that. It also simulates the 8 channel PCM audio chip and the scale and rotation video chip.

  5. #35
    Hedgehog-in-Training Hedgehog-in-TrainingRoad Rasher
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    The exFat mention is curious. I believe there is no BSD- or similar licensed implementation. So either they paid Tuxera (unlikely) or they are using GPL code, meaning their OS will have to be open source or they are violating copyright.

  6. #36
    Nameless One BRNexus7's Avatar
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    Quote Originally Posted by Flygon View Post
    I wonder if they're going to get the MEGA CD emulation accurate enough. That's the part that has me concerned.

    It's a shame they're not making a version that plugs into the expansion slot. There's multiple reasons why this is desirable.
    From a homebrew perspective, it's nice to have a MEGA CD in the expansion slot - bonus soundtrack.
    Can't do that with the MEGA CD in the cartridge slot!

    We'll see - I've learnt from other people that waiting until after launch for TerraOnion hardware is a smart idea. For all the bugs to be found and squashed.
    Pretty sure MegaSD fully supports Piers Solar Cart+CD audio, so homebrew community is not being held back. In fact its super pro homebrew community with the ability to easily enhance Genesis audio with CD quality audio like MSU1 support for SNES.

  7. #37
    Nameless One BRNexus7's Avatar
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    Quote Originally Posted by roce View Post
    The exFat mention is curious. I believe there is no BSD- or similar licensed implementation. So either they paid Tuxera (unlikely) or they are using GPL code, meaning their OS will have to be open source or they are violating copyright.
    They are using the FX68K core for their 68000 implmentation. This core is currently being used on basically every MiSTer core that uses a 68K.

  8. #38
    Hedgehog-in-Training Hedgehog-in-TrainingRoad Rasher
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    The exfat wikipedia page says it also needs a patent license from Microsoft. I feel they did not pay for a patent license :P

  9. #39
    Shining Hero Joe Redifer's Avatar
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    I don't know which of these threads to post in. I choose this one I guess.

    Anyway, did anyone besides me notice that Batman Returns is running WAY too fast? What could be the reason for this? Now as I understand it, the Sega CD works by rendering the scene in its ASIC as it takes care of the scaling and rotation stuffs. It then sends each image to the Genesis to display as a background plane. But the bandwidth is limited. That's why scaling/rotation stuff could only display at around 15-20fps if they were really lucky. Does the cartridge port have the same bandwidth as the expansion port? If it has more, then maybe we can get higher fps in the existing scaling games. If it's the same, then the FPGA is just rendering it too fast, we're still getting that 15-20fps for Batman Returns, we're just "skipping" frames. I'm amazed that nobody else has mentioned this.

  10. #40
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    Quote Originally Posted by BRNexus7 View Post
    They are using the FX68K core for their 68000 implmentation. This core is currently being used on basically every MiSTer core that uses a 68K.
    A GPLv3 FPGA core too, meaning they have to release the FPGA sources in addition to the OS sources.

  11. #41
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    Quote Originally Posted by BRNexus7 View Post
    You don't need a 400GB card. There are only 200 Sega CD games and most are duplicates. You'll only likely need a 400GB card down the road when there are a bunch of audio enhanced Genesis games for it.

    No, it doesn't overclock Genesis CPU. The Sega CD unit itself has its own 68K CPU clocked at 12.5Mhz, the MegaSD simply simulates that. It also simulates the 8 channel PCM audio chip and the scale and rotation video chip.
    Yes I know, I was just saying Mega CD cpu is actually an overclocked Megadrive cpu (same 68k but at 12Mhz) so I'm amazed they can run a whole system from the pins of the cart in terms of power draw, even if it's simulation. It is curious that software emulation takes much more processing power than the original hardware (that's why the MD can't properly emulate most NES games, etc) whilst hardware emulation (FPGA) does actually use LESS power than the original chips (yes even without the laser the Mega CD is power hungry). I'm curious to see the power draw when flashing or launching the games, also when playing wav files in-game.

    I was talking about 400 gb sd card just because they state it'll be compatible with it and I guess bigger cards draw a bit more power than smaller ones. Also exFat should be more cpu hungry than fat32, albeilt not by much. Also maybe at that price tag they are actually paying for the license, which is kinda strange outside the Microsoft sanctionned hardware ecosystem
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  12. #42
    Nameless One BRNexus7's Avatar
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    Quote Originally Posted by chilled View Post
    Yes I know, I was just saying Mega CD cpu is actually an overclocked Megadrive cpu (same 68k but at 12Mhz) so I'm amazed they can run a whole system from the pins of the cart in terms of power draw, even if it's simulation. It is curious that software emulation takes much more processing power than the original power (that's why the MD can't properly emulate most NES games, etc) whilst hardware emulation (FPGA) does actually use LESS power than the original chips (yes even without the laser the Mega CD is power hungry). I'm curious to see the power draw when flashing or launching the games, also when playing wav files in-game.

    I was talking about 400 gb sd card just because they state it'll be compatible with it and I guess bigger cards draw a bit more power than smaller ones. Also exFat should be more cpu hungry than fat32, albeilt not by much. Also maybe at that price tag they are actually paying for the license, which is kinda strange outside the Microsoft sanctionned hardware ecosystem
    MegaSD does support Fat32 as well.

  13. #43
    16-bits is all he needs Master of Shinobi matteus's Avatar
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    Gonna see a mass increase in the number of ISO/BINs on the net then :P plus I guess the Sega CD mini will be the next product Sega produce ha!


  14. #44
    Nameless One BRNexus7's Avatar
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    Quote Originally Posted by Joe Redifer View Post
    I don't know which of these threads to post in. I choose this one I guess.

    Anyway, did anyone besides me notice that Batman Returns is running WAY too fast? What could be the reason for this? Now as I understand it, the Sega CD works by rendering the scene in its ASIC as it takes care of the scaling and rotation stuffs. It then sends each image to the Genesis to display as a background plane. But the bandwidth is limited. That's why scaling/rotation stuff could only display at around 15-20fps if they were really lucky. Does the cartridge port have the same bandwidth as the expansion port? If it has more, then maybe we can get higher fps in the existing scaling games. If it's the same, then the FPGA is just rendering it too fast, we're still getting that 15-20fps for Batman Returns, we're just "skipping" frames. I'm amazed that nobody else has mentioned this.
    From one of the engineers at TerraOnion.

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  15. #45
    Hedgehog-in-Training Hedgehog-in-TrainingRoad Rasher
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    There is a big difference between ASIC and FPGA power consumption, but it's indeed possible for a modern FPGA to use less power than a 30 year old ASIC for the same thing.

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