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[Core/VDP] added some precision in comments about delay on invalid VRAM writes

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EkeEke 2013-10-28 22:06:28 +01:00 committed by twinaphex
parent 9be11710f2
commit a8184dad2e
1 changed files with 11 additions and 5 deletions
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14
core/vdp_ctrl.c
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@ -805,10 +805,16 @@ void vdp_68k_ctrl_w(unsigned int data)
/* /*
FIFO emulation (Chaos Engine/Soldier of Fortune, Double Clutch, Sol Deace) FIFO emulation (Chaos Engine/Soldier of Fortune, Double Clutch, Sol Deace)
-------------------------------------------------------------------------- --------------------------------------------------------------------------
Each VRAM access is byte wide, so one VRAM write (word) need twice cycles. Each VRAM access is byte wide, so one VRAM write (word) need two slot access.
Note: Invalid code 0x02 (register write) apparently behaves the same as VRAM NOTE: Invalid code 0x02 (register write) should not behave the same as VRAM
access, although no data is written in this case (fixes Clue menu) 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.
*/ */
fifo_byte_access = ((code & 0x0F) <= 0x02); fifo_byte_access = ((code & 0x0F) <= 0x02);
} }
@ -2303,7 +2309,7 @@ static void vdp_bus_w(unsigned int data)
default: default:
{ {
/* add some delay until 68k periodical wait-states (RAM refresh ?) are accurately emulated (needed by "Clue" & "Microcosm") */ /* add some delay until 68k periodical wait-states are accurately emulated ("Clue", "Microcosm") */
m68k.cycles += 2; m68k.cycles += 2;
#ifdef LOGERROR #ifdef LOGERROR
error("[%d(%d)][%d(%d)] Invalid (%d) 0x%x write -> 0x%x (%x)\n", v_counter, m68k.cycles/MCYCLES_PER_LINE-1, m68k.cycles, m68k.cycles%MCYCLES_PER_LINE, code, addr, data, m68k_get_reg(M68K_REG_PC)); error("[%d(%d)][%d(%d)] Invalid (%d) 0x%x write -> 0x%x (%x)\n", v_counter, m68k.cycles/MCYCLES_PER_LINE-1, m68k.cycles, m68k.cycles%MCYCLES_PER_LINE, code, addr, data, m68k_get_reg(M68K_REG_PC));