LIJI32/SameBoy
1
0
Fork 0
mirror of https://github.com/LIJI32/SameBoy.git synced 2026-10-12 02:06:38 +00:00
Code Issues Packages Projects Releases Wiki Activity

Basic emulation of CGB<C NR43 glitches

Browse Source
This commit is contained in:
Lior Halphon
2026-02-01 18:10:53 +02:00
parent 7cf082bcc4
commit d1a7f863d4
2 changed files with 16 additions and 5 deletions
Download Patch File Download Diff File Expand all files Collapse all files
Core/apu.c
+15 -4
View File
@@ -1347,7 +1347,11 @@ static void nr43_write(GB_gameboy_t *gb, uint8_t new)
TODO: Non-determinism aside, this is currently only 100% accurate in CGB-E mode, where
my specific CGB-E is currently emulated. My CGB-D, under rare cases, samples a second
intermediate value, and this is not currently emulated. AGB revisions are extremely
glitchy, and are hard to research. Pre-CGB-D revisions are WIP.
glitchy, and are hard to research.
Due to FF-write glitches in pre-CGB-D revisions, all writes (even no-change writes) go
through 3 intermediate values by definition. Also, the effective counter value used is
ORed with the next (or previous, timing needs to be verified) value.
*/
bool old_narrow = gb->apu.noise_channel.narrow;
gb->apu.noise_channel.narrow = new & 8;
@@ -1356,11 +1360,15 @@ static void nr43_write(GB_gameboy_t *gb, uint8_t new)
if ((old & 0xF0) == (new & 0xF0)) return;
bool old_bit = (gb->apu.noise_channel.counter >> (old >> 4)) & 1;
uint16_t effective_counter = gb->apu.noise_channel.counter;
if (gb->model <= GB_MODEL_CGB_C) {
effective_counter |= (effective_counter - 1) & 0x3FFF;
}
bool old_bit = (effective_counter >> (old >> 4)) & 1;
uint8_t glitch_value = (old & 0x7F) | (new & 0x80);
bool glitch_bit = (gb->apu.noise_channel.counter >> (glitch_value >> 4)) & 1;
bool new_bit = (gb->apu.noise_channel.counter >> (new >> 4)) & 1;
bool glitch_bit = (effective_counter >> (glitch_value >> 4)) & 1;
bool new_bit = (effective_counter >> (new >> 4)) & 1;
bool force_glitch = false;
if (gb->model == GB_MODEL_CGB_D) {
@@ -2037,6 +2045,9 @@ void GB_apu_write(GB_gameboy_t *gb, uint8_t reg, uint8_t value)
divisor + (divisor == 2? 0 : inline_const(uint8_t[], {2, 1, 4, 3})[(gb->apu.noise_channel.alignment) & 3]);
}
}
if (gb->model <= GB_MODEL_CGB_C) {
nr43_write(gb, 0xff);
}
nr43_write(gb, value);
break;
Core/apu.h
+1 -1
View File
@@ -157,7 +157,7 @@ typedef struct
bool noise_counter_active;
bool noise_background_counter_active;
bool lfsr_stepped_in_narrow;
bool lfsr_bit_7_before_step; // Used by some corrputions?
bool lfsr_bit_7_before_step; // Used by some corruptions?
} GB_apu_t;
typedef enum {