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https://github.com/ekeeke/Genesis-Plus-GX.git
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80 lines
3.1 KiB
Plaintext
80 lines
3.1 KiB
Plaintext
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Here are some technical details about things that need to be fixed or
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added to Genesis Plus.
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Missing features:
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- Support for 6-button controllers
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- SRAM management
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- Game Genie / PAR patch codes
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The VDP code could use a lot of cleaning up.
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The rendering code is missing a few bits:
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- Sprite collision
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- Window bug
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I think the "C" 68000 emulator either has some bugs or I'm not using it
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correctly. Older DOS-only versions used Turbo68K, which had ran games
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much better, especially with regards to interrupt handling.
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Things that need to be fixed:
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- Raster garbage on third road in Thunder Blade.
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- Added country codes for Dragon Slayer, but game locks up after
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passing country check.
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- No inputs in Samurai Shodown.
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(This game doesn't initialize the port direction registers, at least not
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directly. Emulation bug or problem with the game?)
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- Palette and raster problems in Mortal Kombat.
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- Bad raster effects and VRAM corruption in Super Skidmarks.
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(Needs PAL timing)
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- Palette problems in Sonic 2 title screen.
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- Masked half of Sonic sprite visible on Sonic title screen.
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- Sprite masking doesn't work in Micro Machines subscreen.
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- Music has slow tempo in Batman & Robin. (doesn't seem to be a problem
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with the YM2612 timers - Wonderboy 3 is normal)
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- Music has jerky playback in Sonic 2, 3, 3D Blast. If you run the Z80
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emulation for one scanline after requesting an interrupt, it runs fine.
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- DAC and PSG output are too loud, both are divided by two for now
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(though the PSG should be a bit quieter and the DAC a bit louder)
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- Undead Line locks after selecting a stage, also the Z80 sound halts
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after the first note is played.
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This game single steps the Z80 with the following code:
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MOVEM.L D0,-(A7) ; 009C7C 48 E7 80 00
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ORI #$0200,SR ; 009C80 00 7C 02 00
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; Get control of the Z-bus
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MOVE.W #$0100,$00A11100 ; 009C84 33 FC 01 00 00 A1 11 00
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BTST #$00,$00A11100 ; 009C8C 08 39 00 00 00 A1 11 00
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BNE.S *-$08 [00009C8C] ; 009C94 66 F6
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; Check driver status byte. If zero, release bus and exit.
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TST.B $00A00008 ; 009C96 4A 39 00 A0 00 08
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BEQ *+$0016 [00009CB2] ; 009C9C 67 00 00 14
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; Release bus and wait for Z80 to resume control. Then restart the loop
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; and immediately get the bus back again, assuming the Z80 ran at least
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; one instruction in the meantime.
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CLR.W $00A11100 ; 009CA0 42 79 00 A1 11 00
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BTST #$00,$00A11100 ; 009CA6 08 39 00 00 00 A1 11 00
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BEQ.S *-$08 [00009CA6] ; 009CAE 67 F6
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BRA.S *-$2C [00009C84] ; 009CB0 60 D2
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; Release bus and exit.
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CLR.W $00A11100 ; 009CB2 42 79 00 A1 11 00
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ANDI #$FDFF,SR ; 009CB8 02 7C FD FF
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MOVEM.L (A7)+,D0 ; 009CBC 4C DF 00 01
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RTS ; 009CC0 4E 75
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