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Post by evildragon on Sept 18, 2007 1:43:08 GMT -5
Is it possible to write a program that shows how much RAM you have in your Genesis?
I plan to do a RAM upgrade mod, and want a program to show if it's successful or not.
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oompa loompa
I AM THE GOVERNATOR
"Git 'Er Dun!"
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Post by oompa loompa on Sept 19, 2007 0:35:00 GMT -5
to detect how much usable ram is in your genesis, you'll need to make some kind of memory checker program. what they do is that they'll write different sets of data to certain locations of ram, and it will then read that data back to compare it with what it write, so that it can determine how much actual ram is there.
i wouldn't write such a thing in basiegaxorz because the running code rellies on certain areas of ram (for the heap, variables, stack, system pointers, etc)
basiegaxorz programs, and 100% of all sega genesis games only use the 64k of stock work ram
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Post by evildragon on Sept 19, 2007 1:35:02 GMT -5
to detect how much usable ram is in your genesis, you'll need to make some kind of memory checker program. what they do is that they'll write different sets of data to certain locations of ram, and it will then read that data back to compare it with what it write, so that it can determine how much actual ram is there. i wouldn't write such a thing in basiegaxorz because the running code rellies on certain areas of ram (for the heap, variables, stack, system pointers, etc) basiegaxorz programs, and 100% of all sega genesis games only use the 64k of stock work ram yea, i know that the games only use it.. but i want to try assembly, and want to have 128k of RAM access..
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Post by jlf65 on Sept 29, 2007 6:03:05 GMT -5
to detect how much usable ram is in your genesis, you'll need to make some kind of memory checker program. what they do is that they'll write different sets of data to certain locations of ram, and it will then read that data back to compare it with what it write, so that it can determine how much actual ram is there. i wouldn't write such a thing in basiegaxorz because the running code rellies on certain areas of ram (for the heap, variables, stack, system pointers, etc) basiegaxorz programs, and 100% of all sega genesis games only use the 64k of stock work ram yea, i know that the games only use it.. but i want to try assembly, and want to have 128k of RAM access.. Only 128K? That's pretty worthless. Why not bump that to what space is available there - 2MB? Now THAT would be a lot more useful. It probably costs less for 2MB than for that extra 64K as well.
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Post by evildragon on Sept 29, 2007 7:23:22 GMT -5
yea, i know that the games only use it.. but i want to try assembly, and want to have 128k of RAM access.. Only 128K? That's pretty worthless. Why not bump that to what space is available there - 2MB? Now THAT would be a lot more useful. It probably costs less for 2MB than for that extra 64K as well. Can that even be addressed by the Genesis without too much modification?
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Post by GiGaBiTe on Dec 10, 2007 6:50:57 GMT -5
Only 128K? That's pretty worthless. Why not bump that to what space is available there - 2MB? Now THAT would be a lot more useful. It probably costs less for 2MB than for that extra 64K as well. Can that even be addressed by the Genesis without too much modification? The MC68000 has a 24 bit address bus so it can access a maximum of 16M of memory at a time. You could probably do some funky bank switching by lowering the maximum memory to 8M to have significantly more RAM in 8M pages, but managing memory banks can be a pain in the ass. Also, the ROM limit is 4M without using bank switching so having 16M of memory is mostly useless unless you plan on loading stuff from a Sega CD. It could probably be useful for having a lot of graphical data if used correctly.
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Post by jlf65 on Dec 12, 2007 5:41:57 GMT -5
Can that even be addressed by the Genesis without too much modification? The MC68000 has a 24 bit address bus so it can access a maximum of 16M of memory at a time. You could probably do some funky bank switching by lowering the maximum memory to 8M to have significantly more RAM in 8M pages, but managing memory banks can be a pain in the ass. Also, the ROM limit is 4M without using bank switching so having 16M of memory is mostly useless unless you plan on loading stuff from a Sega CD. It could probably be useful for having a lot of graphical data if used correctly. He was referring to my comment on 2M of work ram. There is 2M of space allocated in the map for work ram, and people have been able to extend the work ram to various amounts - I've seen reports up to 256K. Whether or not the full 2M of space can be work ram remains to be seen... someone would actually have to make the mod and see if all 2M are visible in the space. My guess would be that it is. They probably use the minimum number of address lines to decode the map, and that means it would activate the work ram select for the maximum amount of memory. I'd use a 16 Mbit (1M x 16) SRAM.
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oompa loompa
I AM THE GOVERNATOR
"Git 'Er Dun!"
Posts: 1,301
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Post by oompa loompa on Dec 13, 2007 14:51:32 GMT -5
I modded my sega genesis to use 128k of work ram. i only replaced the 32k srams with a socket, and then use two 64k assync srams (from a 486 cache). I think it can be expanded even more, but I actually didn't need all that sram space for my os
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Post by jlf65 on Dec 13, 2007 19:35:17 GMT -5
I modded my sega genesis to use 128k of work ram. i only replaced the 32k srams with a socket, and then use two 64k assync srams (from a 486 cache). I think it can be expanded even more, but I actually didn't need all that sram space for my os I'm looking around for some 1Mx8 SRAMs to replace the 32k SRAMs. I've found a couple different ones, but they don't seem to be sold to regular folks. Having 2M of work ram would be good for doing things like a 32X/CD version of DOOM where you need extra ram for level and texture data. Games like DOOM traditionally use the ROM for that, but I'd rather have it loading off the CD. Having 2M of work ram would also make the main 68k more useful for SEGA CD games as you'd have a lot more room for code for the main 68k without having to use the bank memory from the CD.
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Post by jlf65 on Dec 15, 2007 3:05:21 GMT -5
This was posted over at SpritesMind.net:
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