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Pixel accurate emulation of Prehistorik Man on a CGB-CPU-E

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This commit is contained in:
Lior Halphon 2018-06-08 18:44:03 +03:00
parent ca01ff6f79
commit 593cb7c107
1 changed files with 46 additions and 30 deletions
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74
Core/z80_cpu.c
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@ -11,13 +11,13 @@ typedef enum {
GB_CONFLICT_READ_OLD,
/* If the CPU writes while another component reads, it reads the new value */
GB_CONFLICT_READ_NEW,
/* If the CPU writes while another component reads, it reads a bitwise OR between the new and old values */
GB_CONFLICT_READ_OR,
/* If the CPU and another component write at the same time, the CPU's value "wins" */
GB_CONFLICT_WRITE_CPU,
/* Register specific values */
GB_CONFLICT_STAT_CGB,
GB_CONFLICT_STAT_DMG,
GB_CONFLICT_PALETTE_DMG,
GB_CONFLICT_PALETTE_CGB,
} GB_conflict_t;
/* Todo: How does double speed mode affect these? */
@ -25,6 +25,10 @@ static const GB_conflict_t cgb_conflict_map[0x80] = {
[GB_IO_IF] = GB_CONFLICT_WRITE_CPU,
[GB_IO_LYC] = GB_CONFLICT_WRITE_CPU,
[GB_IO_STAT] = GB_CONFLICT_STAT_CGB,
[GB_IO_BGP] = GB_CONFLICT_PALETTE_CGB,
[GB_IO_OBP0] = GB_CONFLICT_PALETTE_CGB,
[GB_IO_OBP1] = GB_CONFLICT_PALETTE_CGB,
/* Todo: most values not verified, and probably differ between revisions */
};
@ -37,9 +41,9 @@ static const GB_conflict_t dmg_conflict_map[0x80] = {
[GB_IO_STAT] = GB_CONFLICT_STAT_DMG,
/* Todo: these are GB_CONFLICT_READ_NEW on MGB/SGB2 */
[GB_IO_BGP] = GB_CONFLICT_READ_OR,
[GB_IO_OBP0] = GB_CONFLICT_READ_OR,
[GB_IO_OBP1] = GB_CONFLICT_READ_OR,
[GB_IO_BGP] = GB_CONFLICT_PALETTE_DMG,
[GB_IO_OBP0] = GB_CONFLICT_PALETTE_DMG,
[GB_IO_OBP1] = GB_CONFLICT_PALETTE_DMG,
/* Todo: these were not verified at all */
[GB_IO_WY] = GB_CONFLICT_READ_NEW,
@ -88,22 +92,30 @@ static void cycle_write(GB_gameboy_t *gb, uint16_t addr, uint8_t value)
gb->pending_cycles = 5;
return;
case GB_CONFLICT_READ_OR: {
GB_advance_cycles(gb, gb->pending_cycles - 2);
uint8_t old_value = GB_read_memory(gb, addr);
GB_write_memory(gb, addr, value | old_value);
GB_advance_cycles(gb, 1);
GB_write_memory(gb, addr, value);
gb->pending_cycles = 5;
return;
}
case GB_CONFLICT_WRITE_CPU:
GB_advance_cycles(gb, gb->pending_cycles + 1);
GB_write_memory(gb, addr, value);
gb->pending_cycles = 3;
return;
/* The DMG STAT-write bug is basically the STAT register being read as FF for a single T-cycle */
case GB_CONFLICT_STAT_DMG:
GB_advance_cycles(gb, gb->pending_cycles);
/* State 7 is the edge between HBlank and OAM mode, and it behaves a bit weird.
The OAM interrupt seems to be blocked by HBlank interrupts in that case, despite
the timing not making much sense for that.
This is a hack to simulate this effect */
if (gb->display_state == 7 && (gb->io_registers[GB_IO_STAT] & 0x28) == 0x08) {
GB_write_memory(gb, addr, ~0x20);
}
else {
GB_write_memory(gb, addr, 0xFF);
}
GB_advance_cycles(gb, 1);
GB_write_memory(gb, addr, value);
gb->pending_cycles = 3;
return;
case GB_CONFLICT_STAT_CGB: {
/* The LYC bit behaves differently */
uint8_t old_value = GB_read_memory(gb, addr);
@ -115,23 +127,27 @@ static void cycle_write(GB_gameboy_t *gb, uint16_t addr, uint8_t value)
return;
}
/* The DMG STAT-write bug is basically the STAT register being read as FF for a single T-cycle */
case GB_CONFLICT_STAT_DMG:
GB_advance_cycles(gb, gb->pending_cycles);
/* State 7 is the edge between HBlank and OAM mode, and it behaves a bit weird.
The OAM interrupt seems to be blocked by HBlank interrupts in that case, despite
the timing not making much sense for that.
This is a hack to simulate this effect */
if (gb->display_state == 7 && (gb->io_registers[GB_IO_STAT] & 0x28) == 0x08) {
GB_write_memory(gb, addr, ~0x20);
}
else {
GB_write_memory(gb, addr, 0xFF);
}
/* There is some "time travel" going on with these two values, as it appears
that there's some off-by-1-T-cycle timing issue in the PPU implementation.
This is should be accurate for every measureable scenario, though. */
case GB_CONFLICT_PALETTE_DMG: {
GB_advance_cycles(gb, gb->pending_cycles - 2);
uint8_t old_value = GB_read_memory(gb, addr);
GB_write_memory(gb, addr, value | old_value);
GB_advance_cycles(gb, 1);
GB_write_memory(gb, addr, value);
gb->pending_cycles = 3;
gb->pending_cycles = 5;
return;
}
case GB_CONFLICT_PALETTE_CGB: {
GB_advance_cycles(gb, gb->pending_cycles - 2);
GB_write_memory(gb, addr, value);
gb->pending_cycles = 6;
return;
}
}
}