Size limits

For anything related to cart (SRAM, SF2 mapper, audio, CD mode 1, ...)

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cero
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Re: Size limits

Post by cero » Tue Apr 16, 2019 5:13 pm

I think many emulators don't bother implementing any limit (beyond a 8-bit var). IIRC I tested mednafen and/or dgen.

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Stef
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Re: Size limits

Post by Stef » Tue Apr 16, 2019 5:18 pm

About Bank switch ? in fact i don't know any emulator which does really support generic bank switch (Gens limit to 8 MB for instance and i know some others just support SSF2 in a hacky way).
Last edited by Stef on Wed Apr 17, 2019 7:56 am, edited 1 time in total.

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Sik
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Re: Size limits

Post by Sik » Tue Apr 16, 2019 9:36 pm

Fusion is limited to 6MB, Regen is limited to 5MB, yeah.

BlastEm seems like it may support 128MB, though no guarantees on this as nobody has attempted that yet. The header needs to have "SEGA SSF2" instead of "SEGA MEGA DRIVE" to enable this, however (real hardware doesn't care, mind you). You'll probably want a custom flashcart to test it on real hardware too…
Sik is pronounced as "seek", not as "sick".

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Re: Size limits

Post by Chilly Willy » Tue Apr 16, 2019 11:58 pm

Jorge is making a few Giga carts sometime this year. I've arranged to get two from him when he does.

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Re: Size limits

Post by mix256 » Wed Apr 17, 2019 11:44 am

Sik wrote:
Tue Apr 16, 2019 9:36 pm
Fusion is limited to 6MB, Regen is limited to 5MB, yeah.

BlastEm seems like it may support 128MB, though no guarantees on this as nobody has attempted that yet. The header needs to have "SEGA SSF2" instead of "SEGA MEGA DRIVE" to enable this, however (real hardware doesn't care, mind you). You'll probably want a custom flashcart to test it on real hardware too…
Tempted to fool around with my bread board. Been a while. Using a RAM, the turnaround time for testing would be quite fast as well. I guess.
Chilly Willy wrote:
Tue Apr 16, 2019 11:58 pm
Jorge is making a few Giga carts sometime this year. I've arranged to get two from him when he does.
What does this board contain? I'm definitely interested in this as well.

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Re: Size limits

Post by Chilly Willy » Wed Apr 17, 2019 1:19 pm

128MB (1Gbit) of flash, and 2MB of save ram, IIRC. It uses the standard SEGA mapper with all 8 bits of the bank registers implemented. It uses level shifters to interface with the 3V parts. And that's it. Just a straightforward BIG flash cart.

Jorge has a special box he made to flash carts like this, but you can also put a piece of tape over the /CART line and boot a CD to write the flash on a MD/CD. That's how I intend to program mine... when he gets around to making them. :D

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Re: Size limits

Post by mix256 » Thu Apr 18, 2019 12:49 pm

Chilly Willy wrote:
Wed Apr 17, 2019 1:19 pm
128MB (1Gbit) of flash, and 2MB of save ram, IIRC. It uses the standard SEGA mapper with all 8 bits of the bank registers implemented. It uses level shifters to interface with the 3V parts. And that's it. Just a straightforward BIG flash cart.

Jorge has a special box he made to flash carts like this, but you can also put a piece of tape over the /CART line and boot a CD to write the flash on a MD/CD. That's how I intend to program mine... when he gets around to making them. :D
If I'm going to continue doing the "one huge background image" for PLANE_B in my shmup, I really need to decide on this since each screen will take up 36K. Aaaargh, the pressure. :)

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Sik
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Re: Size limits

Post by Sik » Thu Apr 18, 2019 5:37 pm

Wait, it's for that shmup where you were using a map photo for the background? I mean, huh, dunno, but maybe it'd be better for you to use pixelart and reuse tiles as needed. There's no reason why you should be spending that much on a scrolling background unless you go full Silpheed with its prerendered 3D graphics.
Sik is pronounced as "seek", not as "sick".

mix256
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Re: Size limits

Post by mix256 » Fri Apr 19, 2019 5:23 am

Sik wrote:
Thu Apr 18, 2019 5:37 pm
Wait, it's for that shmup where you were using a map photo for the background? I mean, huh, dunno, but maybe it'd be better for you to use pixelart and reuse tiles as needed. There's no reason why you should be spending that much on a scrolling background unless you go full Silpheed with its prerendered 3D graphics.
The idea was to use digitized art, like everywhere. Doing irl models, scan heightmaps, rendered/filmed cut scenes. Thundercade and Twin Eagle being main inspirations (and metal black, gun frontier etc).
But it's getting a bit daunting, yes. :)

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Re: Size limits

Post by Hpman » Wed May 01, 2019 2:44 pm

Happen to be disgressing a bit from NeoGeo lately and I did prototype such a Gb card for the megadrive.

Wasn't aware of the !time signal back then so this test card is designed to switch banks by writing to the ROM region (0x0-0x3fffff).

Was able to barely fit 7 selectable windows in CPLD, so it can be configured as either:
- one fixed 512KB region + 7 512KB selectable windows (just fine to create new software)
- 6 512KB selectable windows + 1 1MB selectable window (multigame card setup)

Behold:
Image

Bit of testing the multigame setup:
https://www.youtube.com/watch?v=tJqbVdyV-m8

mix256
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Re: Size limits

Post by mix256 » Thu May 02, 2019 7:19 am

Hpman wrote:
Wed May 01, 2019 2:44 pm
Happen to be disgressing a bit from NeoGeo lately and I did prototype such a Gb card for the megadrive.

Wasn't aware of the !time signal back then so this test card is designed to switch banks by writing to the ROM region (0x0-0x3fffff).

Was able to barely fit 7 selectable windows in CPLD, so it can be configured as either:
- one fixed 512KB region + 7 512KB selectable windows (just fine to create new software)
- 6 512KB selectable windows + 1 1MB selectable window (multigame card setup)

Behold:
Image

Bit of testing the multigame setup:
https://www.youtube.com/watch?v=tJqbVdyV-m8
Beautiful! :D

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Sik
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Re: Size limits

Post by Sik » Thu May 02, 2019 9:29 am

Any chances to adapt it to use /TIME instead to switch banks? (・・?) I'd really prefer if we don't go around coming up with new schemes all over the place (the more standarized we can get the hardware, the easier it becomes to emulate it)

Asking since I imagine that some people may want to use that board now.
Sik is pronounced as "seek", not as "sick".

Hpman
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Re: Size limits

Post by Hpman » Thu May 02, 2019 1:02 pm

Yeah it looks like it's possible with the same CPLD chip (100% macrocell & pin usage, I guess it was made for the task heh).

It might however not 100% replicate the SEGA mapper as there's not enough pins to catch A4-A7.
This means writing 0xA13003 will be the same effect as writing 0xA130F3.

Not a huge deal, however it will bankswitch where the official one supposedly would not (does SSF2 mapper even makes sure thoses bits are set to 1 anyway?)

Could be done with larger CPLD which means larger board & more cost. Meh.

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Re: Size limits

Post by Chilly Willy » Thu May 02, 2019 3:20 pm

It needs to be able to NOT respond to 0xA130EC or it won't work with the 32X.

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Sik
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Re: Size limits

Post by Sik » Thu May 02, 2019 3:50 pm

I thought the 32X caught the $A130EC-$A130EF range and passed along the rest (・~・) (since it can intercept anything that goes through the cartridge slot). Especially given the games that map all of $A130xx to what would be $A130F1 (so basically anything that saves and is larger than 2MB, or Sonic 3 which implements it anyway for the sake of S&K), you'd think those would break spectacularly with the 32X otherwise.

I suppose it's advisable to always explicitly initialize the mapper after checking for 32X tho. First 512KB are always going to be in place anyway.

EDIT: but yeah, that aside, it's common to always ignore the bits that decode addresses that are not meant to be ever touched anyway (hence the whole concept of mirroring).
Last edited by Sik on Thu May 02, 2019 3:56 pm, edited 1 time in total.
Sik is pronounced as "seek", not as "sick".

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