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Post by Deleted on May 19, 2012 13:06:48 GMT -5
Has anyone determined how big a BEX game can get?
Likewise, are BEX SegaCD games limited?
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Post by Deleted on May 19, 2012 19:04:49 GMT -5
You can use the entire ROM area, which is 4 Megabytes / 32 Megabits. Games that are larger require bank switching .. for which BEX doesn't have support build-in ( because this depends on the cartridge mapper ).
SEGA CD programs shouldn't exceed that limit either. But you can have as many programs as you can fit on a 650MB CD .. and ( non-instruction ) data doesn't have to be bound by that limit either.
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Post by Mairtrus on May 20, 2012 11:04:46 GMT -5
Actually, each SCD program can't pass over the boundary of 256 kb, since it's the maximum size of the WRAM (where the SCD programs reside).
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Post by Deleted on May 20, 2012 12:11:06 GMT -5
Oops, did not know that. Thanks for the correction  |
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Post by cleetus on Jun 10, 2012 16:43:25 GMT -5
I wonder if there is a schematics about a simple mapper for the mega drive... Using like 8 megabytes of rom area would be a great thing.  |
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Post by Mairtrus on Jun 11, 2012 9:30:50 GMT -5
I wonder if there is a schematics about a simple mapper for the mega drive... Using like 8 megabytes of rom area would be a great thing. Do you mean 8MB inline, or separated in banks? |
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Post by cleetus on Jun 11, 2012 9:58:28 GMT -5
I think it would be easier to make a mapper with banks.
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Post by Mairtrus on Jun 11, 2012 11:32:05 GMT -5
Both are easy to make, except an straight 8MB cart will cause malfunction in real hardware if you have attached a SEGA-CD.
The simplest mapper I can think now only needs a couple of OR gates, a 2-bit register (a dual flip-flop), and the mask rom, of course. The first bank (000000 to 1FFFFF) is fixed, and with the 2-bit register you can select which bank in physical ROM (0-1, 2-3, 4-5 or 6-7 MB) is visible in the second bank.
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Post by Deleted on Jun 11, 2012 11:38:35 GMT -5
The basic problem with over 4meg binaries is that there are no "mappers" like NES games. There is no standard bank switching scheme that BEX programmers can rely on.
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Post by cleetus on Jun 11, 2012 11:51:15 GMT -5
If i try hard enough, then i could do the mapping in the software. I remember disassembling an Earthworm Jim/Lion King/Rise of the robots cartridge, that they used some minimalistic circuitry to make a 24 megabit cartridge. I don't know how those "mappers" work, but getting another Rotr carrtidge, maybe modifying that would be enugh.
Sega CD is not a problem, the programmer must warn the user to remove the attachment or something.
I tought about this mapper thing, i got two 32megabit eproms, and getting 64mbits for my game would be awesome...
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