libretro/Genesis-Plus-GX
1
0
Fork 0
mirror of https://github.com/libretro/Genesis-Plus-GX.git synced 2024-11-23 08:19:39 +00:00
Code Issues Actions 1 Packages Projects Releases Wiki Activity

[Core/VDP] reverted FIFO access timings hack when using invalid write code value

Browse Source
This commit is contained in:
ekeeke 2024-02-23 11:19:43 +01:00
parent 49a289df89
commit c04a9426b7
2 changed files with 6 additions and 14 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

18
core/vdp_ctrl.c
View File

@ -5,7 +5,7 @@
* Support for SG-1000 (TMS99xx & 315-5066), Master System (315-5124 & 315-5246), Game Gear & Mega Drive VDP
*
* Copyright (C) 1998-2003 Charles Mac Donald (original code)
* Copyright (C) 2007-2023 Eke-Eke (Genesis Plus GX)
* Copyright (C) 2007-2024 Eke-Eke (Genesis Plus GX)
*
* Redistribution and use of this code or any derivative works are permitted
* provided that the following conditions are met:
@ -835,18 +835,12 @@ void vdp_68k_ctrl_w(unsigned int data)
/*
FIFO emulation (Chaos Engine/Soldier of Fortune, Double Clutch, Sol Deace)
--------------------------------------------------------------------------
Each VRAM access is byte wide, so one VRAM write (word) need two slot access.
Each VRAM access is byte wide, so one VRAM write (word) need two access slots.
NOTE: Invalid code 0x02 (register write) should not behave the same as VRAM
access, i.e data is ignored and only one access slot is used for each word,
BUT a few games ("Clue", "Microcosm") which accidentally corrupt code value
will have issues when emulating FIFO timings. They likely work fine on real
hardware because of periodical 68k wait-states which have been observed and
would naturaly add some delay between writes. Until those wait-states are
accurately measured and emulated, delay is forced when invalid code value
is being used.
NOTE: Invalid codes 0x00, 0x08 and 0x09 behaves the same as VRAM access (0x01) i.e,
although no data is written, two access slots are required to empty the FIFO entry.
*/
fifo_byte_access = ((code & 0x0F) <= 0x02);
fifo_byte_access = (code & 0x06) ? 0 : 1;
}
/* Mega Drive VDP control port specific (MS compatibility mode) */
@ -2278,8 +2272,6 @@ static void vdp_bus_w(unsigned int data)
default:
{
/* add some delay until 68k periodical wait-states are accurately emulated ("Clue", "Microcosm") */
m68k.cycles += 2;
#ifdef LOGERROR
error("[%d(%d)][%d(%d)] Invalid (%d) 0x%x write -> 0x%x (%x)\n", v_counter, (v_counter + (m68k.cycles - mcycles_vdp)/MCYCLES_PER_LINE)%lines_per_frame, m68k.cycles, m68k.cycles%MCYCLES_PER_LINE, code, addr, data, m68k_get_reg(M68K_REG_PC));
#endif

2
core/vdp_ctrl.h
View File

@ -5,7 +5,7 @@
* Support for SG-1000 (TMS99xx & 315-5066), Master System (315-5124 & 315-5246), Game Gear & Mega Drive VDP
*
* Copyright (C) 1998-2003 Charles Mac Donald (original code)
* Copyright (C) 2007-2023 Eke-Eke (Genesis Plus GX)
* Copyright (C) 2007-2024 Eke-Eke (Genesis Plus GX)
*
* Redistribution and use of this code or any derivative works are permitted
* provided that the following conditions are met: