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[Core/CD] improved Sub-CPU BUSREQ status accuracy

This commit is contained in:
ekeeke 2023-08-25 16:47:01 +02:00
parent ad706045d3
commit 5a3e18f71b
6 changed files with 39 additions and 20 deletions
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1
HISTORY.txt
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@ -31,6 +31,7 @@ Genesis Plus GX 1.7.5 (xx/xx/xxxx) (Eke-Eke)
* improved Word-RAM byte access accuracy (verified on schematics)
* improved GFX processing accuracy to halt it while Word RAM is allocated to Main CPU in 2M mode
* improved GFX timing accuracy (fixes "Night Striker" crashing after completing a game)
* improved Sub-CPU BUSREQ status accuracy
* disabled 68k and Z80 access to PRG-RAM when SUB-CPU is running (fixes "Dungeon Explorer")
* disabled CD hardware reset on Soft-Reset (verified on real hardware)
* fixed potential load issues with non-zero backup RAM cart

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56
core/mem68k.c
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@ -3,7 +3,7 @@
* Main 68k bus handlers
*
* Copyright (C) 1998-2003 Charles Mac Donald (original code)
* Copyright (C) 2007-2022 Eke-Eke (Genesis Plus GX)
* Copyright (C) 2007-2023 Eke-Eke (Genesis Plus GX)
*
* Redistribution and use of this code or any derivative works are permitted
* provided that the following conditions are met:
@ -696,29 +696,40 @@ void ctrl_io_write_byte(unsigned int address, unsigned int data)
/* RESET bit */
if (data & 0x01)
{
/* trigger reset on 0->1 transition */
/* SUB-CPU reset is triggered on /RESET input 0->1 transition */
if (!(scd.regs[0x00].byte.l & 0x01))
{
/* reset SUB-CPU */
s68k_pulse_reset();
}
/* BUSREQ bit */
if (data & 0x02)
{
/* SUB-CPU bus requested */
/* SUB-CPU is halted (/HALT input is asserted) */
s68k_pulse_halt();
}
else
{
/* SUB-CPU bus released */
/* SUB-CPU is running (/HALT input is released) */
s68k_clear_halt();
}
/* update BUSREQ and RESET bits */
scd.regs[0x00].byte.l = data & 0x03;
}
else
{
/* SUB-CPU is halted while !RESET is asserted */
/* SUB-CPU is halted (/HALT and /RESET inputs are asserted) */
s68k_pulse_halt();
/* RESET bit is cleared and BUSREQ bit is set to 1 (verified on real hardware) */
scd.regs[0x00].byte.l = 0x02;
}
/* BUSREQ bit remains set to 0 if SUB-CPU is halted while stopped (verified on real hardware) */
if (s68k.stopped & 0x01)
{
scd.regs[0x00].byte.l &= ~0x02;
}
/* check if SUB-CPU halt status has changed */
@ -727,8 +738,8 @@ void ctrl_io_write_byte(unsigned int address, unsigned int data)
/* PRG-RAM (128KB bank) is normally mapped to $020000-$03FFFF (resp. $420000-$43FFFF) */
unsigned int base = scd.cartridge.boot + 0x02;
/* PRG-RAM can only be accessed from MAIN 68K & Z80 when SUB-CPU is halted (Dungeon Explorer USA version) */
if ((data & 0x03) != 0x01)
/* PRG-RAM can only be accessed from MAIN-CPU & Z80 when BUSREQ bit is set (Dungeon Explorer USA version) */
if (scd.regs[0x00].byte.l & 0x02)
{
m68k.memory_map[base].read8 = m68k.memory_map[base+1].read8 = NULL;
m68k.memory_map[base].read16 = m68k.memory_map[base+1].read16 = NULL;
@ -748,7 +759,6 @@ void ctrl_io_write_byte(unsigned int address, unsigned int data)
}
}
scd.regs[0x00].byte.l = data;
return;
}
@ -934,29 +944,40 @@ void ctrl_io_write_word(unsigned int address, unsigned int data)
/* RESET bit */
if (data & 0x01)
{
/* trigger reset on 0->1 transition */
/* SUB-CPU reset is triggered on /RESET input 0->1 transition */
if (!(scd.regs[0x00].byte.l & 0x01))
{
/* reset SUB-CPU */
s68k_pulse_reset();
}
/* BUSREQ bit */
if (data & 0x02)
{
/* SUB-CPU bus requested */
/* SUB-CPU is halted (/HALT input is asserted) */
s68k_pulse_halt();
}
else
{
/* SUB-CPU bus released */
/* SUB-CPU is running (/HALT input is released) */
s68k_clear_halt();
}
/* update BUSREQ and RESET bits */
scd.regs[0x00].byte.l = data & 0x03;
}
else
{
/* SUB-CPU is halted while !RESET is asserted */
/* SUB-CPU is halted (/HALT and /RESET inputs are asserted) */
s68k_pulse_halt();
/* RESET bit is cleared and BUSREQ bit is set to 1 (verified on real hardware) */
scd.regs[0x00].byte.l = 0x02;
}
/* BUSREQ bit remains set to 0 if SUB-CPU is halted while stopped (verified on real hardware) */
if (s68k.stopped & 0x01)
{
scd.regs[0x00].byte.l &= ~0x02;
}
/* check if SUB-CPU halt status has changed */
@ -965,8 +986,8 @@ void ctrl_io_write_word(unsigned int address, unsigned int data)
/* PRG-RAM (128KB bank) is normally mapped to $020000-$03FFFF (resp. $420000-$43FFFF) */
unsigned int base = scd.cartridge.boot + 0x02;
/* PRG-RAM can only be accessed from MAIN 68K & Z80 when SUB-CPU is halted (Dungeon Explorer USA version) */
if ((data & 0x03) != 0x01)
/* PRG-RAM can only be accessed from MAIN-CPU & Z80 when BUSREQ bit is set (Dungeon Explorer USA version) */
if (scd.regs[0x00].byte.l & 0x02)
{
m68k.memory_map[base].read8 = m68k.memory_map[base+1].read8 = NULL;
m68k.memory_map[base].read16 = m68k.memory_map[base+1].read16 = NULL;
@ -1002,9 +1023,6 @@ void ctrl_io_write_word(unsigned int address, unsigned int data)
s68k_update_irq((scd.pending & scd.regs[0x32>>1].byte.l) >> 1);
}
}
/* update LSB only */
scd.regs[0x00].byte.l = data & 0xff;
return;
}

2
core/mem68k.h
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@ -3,7 +3,7 @@
* Main 68k bus handlers
*
* Copyright (C) 1998-2003 Charles Mac Donald (original code)
* Copyright (C) 2007-2022 Eke-Eke (Genesis Plus GX)
* Copyright (C) 2007-2023 Eke-Eke (Genesis Plus GX)
*
* Redistribution and use of this code or any derivative works are permitted
* provided that the following conditions are met: