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[Core/CPU] fixed 68k cycle counter Power-ON value (verified on real hardware)

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This commit is contained in:
EkeEke 2016-10-15 14:06:23 +02:00
parent e7e19c78dd
commit 2a410a66a9
2 changed files with 26 additions and 11 deletions
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33
core/genesis.c
View File

@ -4,8 +4,8 @@
*
* Support for SG-1000, Mark-III, Master System, Game Gear, Mega Drive & Mega CD hardware
*
* Copyright (C) 1998, 1999, 2000, 2001, 2002, 2003 Charles Mac Donald (original code)
* Copyright (C) 2007-2014 Eke-Eke (Genesis Plus GX)
* Copyright (C) 1998-2003 Charles Mac Donald (original code)
* Copyright (C) 2007-2016 Eke-Eke (Genesis Plus GX)
*
* Redistribution and use of this code or any derivative works are permitted
* provided that the following conditions are met:
@ -234,24 +234,39 @@ void gen_reset(int hard_reset)
/* System Reset */
if (hard_reset)
{
/* clear RAM (TODO: use random bit patterns for all systems, like on real hardware) */
/* On hard reset, 68k CPU always starts at the same point in VDP frame */
/* Tests performed on VA4 PAL MD1 showed that the first HVC value read */
/* with 'move.w #0x8104,0xC00004' , 'move.w 0xC00008,%d0' sequence was */
/* 0x9F21 in 60HZ mode (0x9F00 if Mode 5 is not enabled by first MOVE) */
/* 0x8421 in 50HZ mode (0x8400 if Mode 5 is not enabled by first MOVE) */
/* Same value is returned on every power ON, indicating VDP is always */
/* starting at the same fixed point in frame (probably at the start of */
/* VSYNC and HSYNC) while 68k /VRES line remains asserted a fixed time */
/* after /SRES line has been released (13 msec approx). The difference */
/* between PAL & NTSC is caused by the top border area being 27 lines */
/* larger in PAL mode than in NTSC mode. CPU cycle counter is adjusted */
/* to match these results (taking in account emulated frame is started */
/* on line 192 */
m68k.cycles = ((lines_per_frame - 192 + 159 - (27 * vdp_pal)) * MCYCLES_PER_LINE) + 1004;
/* clear RAM (on real hardware, RAM values are random / undetermined on Power ON) */
memset(work_ram, 0x00, sizeof (work_ram));
memset(zram, 0x00, sizeof (zram));
}
else
{
/* when RESET button is pressed, 68k could be anywhere in VDP frame (Bonkers, Eternal Champions, X-Men 2) */
m68k.cycles = (uint32)((MCYCLES_PER_LINE * lines_per_frame) * ((double)rand() / (double)RAND_MAX));
/* reset YM2612 (on hard reset, this is done by sound_reset) */
fm_reset(0);
}
/* 68k & Z80 could be anywhere in VDP frame (Bonkers, Eternal Champions, X-Men 2) */
m68k.cycles = Z80.cycles = (uint32)((MCYCLES_PER_LINE * lines_per_frame) * ((double)rand() / (double)RAND_MAX));
/* 68k cycles should be a multiple of 7 */
/* 68k M-cycles should be a multiple of 7 */
m68k.cycles = (m68k.cycles / 7) * 7;
/* Z80 cycles should be a multiple of 15 */
Z80.cycles = (Z80.cycles / 15) * 15;
/* Z80 M-cycles should be a multiple of 15 */
Z80.cycles = (m68k.cycles / 15) * 15;
/* 8-bit / 16-bit modes */
if ((system_hw & SYSTEM_PBC) == SYSTEM_MD)

4
core/genesis.h
View File

@ -4,8 +4,8 @@
*
* Support for SG-1000, Mark-III, Master System, Game Gear, Mega Drive & Mega CD hardware
*
* Copyright (C) 1998, 1999, 2000, 2001, 2002, 2003 Charles Mac Donald (original code)
* Copyright (C) 2007-2014 Eke-Eke (Genesis Plus GX)
* Copyright (C) 1998-2003 Charles Mac Donald (original code)
* Copyright (C) 2007-2016 Eke-Eke (Genesis Plus GX)
*
* Redistribution and use of this code or any derivative works are permitted
* provided that the following conditions are met: