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Post by uprock7 on Apr 29, 2013 13:23:25 GMT -5
hey all, i am inspired by low budget's super 8 NES rebuild project to rebuild the sega genesis from scratch. Most of the off the shelf ICs in the genesis(68k, z80, ym2612) seem to be easy enough to find on the internet, but the custom ICs like the vdp and the io controllers are a bit of a puzzle. Are there any available vdp or io clones or compatible ic's anywhere? or would i have to emulate the ic's somehow?
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Post by Deleted on Apr 29, 2013 20:36:57 GMT -5
The VDP is a stock Yamaha YM7101 Do you already have the ( recently leaked ) service manuals? Such as this one?
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Post by Deleted on Apr 29, 2013 23:26:22 GMT -5
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Post by Deleted on Apr 30, 2013 5:57:43 GMT -5
You know, you could probably build a Sega intellectual property free stand alone 32x. A proper Neptune rebuild would be fantastic yes But i doubt it would be popular among developers, as the 32X further complicates development. The MegaDrive + 32X setup gives you 3 different processors ( two SH-2's + 68K + Z80 ), 2 very different VDP's ( SEGA custom LSI + YM7101 ), and 3 sound "generators" ( PWM + YM2612 + SN76489 ) .. not exactly for the faint of heart ;D + In case you're going to bring up BEX as environment to create 32X games. Even when compiling for 32X, BEX only uses the 68K ( 7.67 MHz ) and completely ignores the two SH-2's ( 23.011 MHz each ). So it's only for extremely lightweight games and playing around.
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Post by Deleted on Apr 30, 2013 7:03:28 GMT -5
You know, you could probably build a Sega intellectual property free stand alone 32x. A proper Neptune rebuild would be fantastic yes But i doubt it would be popular among developers, as the 32X further complicates development. The MegaDrive + 32X setup gives you 3 different processors ( two SH-2's + 68K + Z80 ), 2 very different VDP's ( SEGA custom LSI + YM7101 ), and 3 sound "generators" ( PWM + YM2612 + SN76489 ) .. not exactly for the faint of heart ;D + In case you're going to bring up BEX as environment to create 32X games. Even when compiling for 32X, BEX only uses the 68K ( 7.67 MHz ) and completely ignores the two SH-2's ( 23.011 MHz each ). So it's only for extremely lightweight games and playing around. Nothing wrong with lightweight games and playing around. Were you expecting a port of Quake 3 straight away?
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Post by Deleted on Apr 30, 2013 7:24:10 GMT -5
Nothing wrong with lightweight games and playing around. Nothing wrong with that indeed. Just think it's worth mentioning that you won't even get close to using 15% of a MegaDrive + 32X setup ( in terms of performance ) when using BEX
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Post by Deleted on Apr 30, 2013 8:50:21 GMT -5
Interesting point about BEX and compiling for the 32x. It would be almost pointless to develop for the 32x through BEX, aside from just being able to say "I made a 32x game".
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Post by Deleted on Apr 30, 2013 9:36:33 GMT -5
Interesting point about BEX and compiling for the 32x. It would be almost pointless to develop for the 32x through BEX, aside from just being able to say "I made a 32x game". You do get to use the VDP ( using the mars prefixed commands ), but aside from that the 32X is just idling
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Post by uprock7 on Apr 30, 2013 10:36:10 GMT -5
i think for the v1 i would like to just get the genesis portion working and then look into adding sega cd /32x functionality. my initial goals would be to get *good* sound with the YM2612, stereo sound, svideo out, 100% game compatibility, improved power circuits and maybe some way to read ROMs from a SD card. kinda like a built in everdrive
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Post by uprock7 on Apr 30, 2013 12:01:29 GMT -5
does anyone know what the sega 315-5345 IC does?
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Post by Deleted on Apr 30, 2013 14:09:20 GMT -5
does anyone know what the sega 315-5345 IC does? Not exactly sure .. did find a pinout though.
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Post by GiGaBiTe on May 2, 2013 22:00:04 GMT -5
You know, you could probably build a Sega intellectual property free stand alone 32x. A proper Neptune rebuild would be fantastic yes But i doubt it would be popular among developers, as the 32X further complicates development. The MegaDrive + 32X setup gives you 3 different processors ( two SH-2's + 68K + Z80 ), 2 very different VDP's ( SEGA custom LSI + YM7101 ), and 3 sound "generators" ( PWM + YM2612 + SN76489 ) .. not exactly for the faint of heart ;D + In case you're going to bring up BEX as environment to create 32X games. Even when compiling for 32X, BEX only uses the 68K ( 7.67 MHz ) and completely ignores the two SH-2's ( 23.011 MHz each ). So it's only for extremely lightweight games and playing around. If he actually goes through with making a neptune-like console, he could make some drastic improvements to the 32x side. Some things I'd love to see: For starters, using the proper clocks for the dual SH-2s (28.7 MHz.) Long ago, I had access to a 32x that I was able to tinker with. I added heatsinks to both SH2s and disconnected the CLK pins and added a switch so I could use my own clock generator. I tried using the stock clocks (28.7 MHz) and games ran noticeably better. I then did an experiment of clocking the SH-2 that was running the VDP to something like 35 or 40 MHz and it gave massive performance gains. I was able to run Darxide at a solid 30 fps, when normally it was painfully slow on real hardware. The next thing that should be done is expand the bus to be a full 32 bits wide between both SH-2s and the RAM to increase bus bandwidth. At the same time, the painfully slow high latency RAM should be changed out for much faster RAM of higher capacity (IIRC the SH-2 can address 32 MB max) All of these changes could be done without breaking compatibility (except for possibly the RAM.) The genesis side could be upgraded too with more RAM and a faster 68000/68010 that could be clock switched.
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Post by Tiido on May 12, 2013 4:03:00 GMT -5
Problem is that all SDRAM has same kind of latency or even higher. Only some really exotic memories got lower latency and SRAM is the only one with no latency (that you can actually buy). I never succeeded in overclocking a 32X, there were always graphical problems and stability issues... maybe some are more tolerant than others.
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