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Further NR43 write glitch emulation

This commit is contained in:
Lior Halphon 2021-01-10 17:04:16 +02:00
parent 07e76a4ecf
commit e384707615
1 changed files with 32 additions and 16 deletions
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48
Core/apu.c
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@ -710,7 +710,7 @@ uint8_t GB_apu_read(GB_gameboy_t *gb, uint8_t reg)
return gb->io_registers[reg] | read_mask[reg - GB_IO_NR10];
}
static inline uint16_t effective_channel4_counter(GB_gameboy_t *gb)
static inline uint16_t effective_channel4_counter(GB_gameboy_t *gb, uint8_t nr43)
{
uint16_t effective_counter = gb->apu.noise_channel.counter;
/* Ladies and gentlemen, I present you the holy grail glitch of revision detection! */
@ -720,7 +720,14 @@ static inline uint16_t effective_channel4_counter(GB_gameboy_t *gb)
#if 0
case GB_MODEL_CGB_B:
if (effective_counter & 8) {
effective_counter |= 0xE; // Seems to me F under some circumstances?
// Verify this part
if (gb->apu.channel_4_countdown_reloaded && !(effective_counter & 1)) {
uint16_t lower_bits = ~(effective_counter & ~(effective_counter - 1)) & 0xF;
effective_counter = (effective_counter & ~0xF) | lower_bits;
}
else {
effective_counter |= 0xF;
}
}
if (effective_counter & 0x80) {
effective_counter |= 0xFF;
@ -756,7 +763,16 @@ static inline uint16_t effective_channel4_counter(GB_gameboy_t *gb)
// case GB_MODEL_CGB_A:
case GB_MODEL_CGB_C:
if (effective_counter & 8) {
effective_counter |= 0xE;
if (gb->apu.channel_4_countdown_reloaded && !(effective_counter & 1)) {
uint16_t lower_bits = ~(effective_counter & ~(effective_counter - 1)) & 0xF;
effective_counter = (effective_counter & ~0xF) | lower_bits;
if (!(nr43 >> 4)) {
effective_counter &= ~1;
}
}
else {
effective_counter |= 0xE;
}
}
if (effective_counter & 0x80) {
effective_counter |= 0xFF;
@ -820,6 +836,9 @@ static inline uint16_t effective_channel4_counter(GB_gameboy_t *gb)
*/
break;
}
if (gb->model <= GB_MODEL_CGB_C && gb->apu.channel_4_countdown_reloaded && (nr43 >> 4)) {
effective_counter = (effective_counter & effective_counter - 1) | (effective_counter & 1);
}
return effective_counter;
}
@ -1181,16 +1200,22 @@ void GB_apu_write(GB_gameboy_t *gb, uint8_t reg, uint8_t value)
case GB_IO_NR43: {
gb->apu.noise_channel.narrow = value & 8;
uint16_t effective_counter = effective_channel4_counter(gb);
uint16_t effective_counter = effective_channel4_counter(gb, value);
bool old_bit = (effective_counter >> (gb->io_registers[GB_IO_NR43] >> 4)) & 1;
gb->io_registers[GB_IO_NR43] = value;
bool new_bit = (effective_counter >> (gb->io_registers[GB_IO_NR43] >> 4)) & 1;
if (gb->apu.channel_4_countdown_reloaded) {
unsigned divisor = (gb->io_registers[GB_IO_NR43] & 0x07) << 2;
if (!divisor) divisor = 2;
gb->apu.noise_channel.counter_countdown =
divisor + (divisor == 2? 0 : (uint8_t[]){2, 1, 0, 3}[(gb->apu.noise_channel.alignment) & 3]);
gb->apu.channel_4_delta = 0;
if (gb->model > GB_MODEL_CGB_C) {
gb->apu.noise_channel.counter_countdown =
divisor + (divisor == 2? 0 : (uint8_t[]){2, 1, 0, 3}[(gb->apu.noise_channel.alignment) & 3]);
}
else {
gb->apu.noise_channel.counter_countdown =
divisor + (divisor == 2? 0 : (uint8_t[]){2, 1, 4, 3}[(gb->apu.noise_channel.alignment) & 3]);
}
gb->apu.channel_4_delta = 0;
}
/* Step LFSR */
if (new_bit && (!old_bit || gb->model <= GB_MODEL_CGB_C)) {
@ -1238,15 +1263,6 @@ void GB_apu_write(GB_gameboy_t *gb, uint8_t reg, uint8_t value)
}
}
/* TODO: These two are quite weird. Verify further */
if (gb->model <= GB_MODEL_CGB_C && gb->cgb_double_speed) {
if (!(gb->io_registers[GB_IO_NR43] & 0xF0) && (gb->io_registers[GB_IO_NR43] & 0x07)) {
gb->apu.noise_channel.counter_countdown -= 1;
}
else if ((gb->io_registers[GB_IO_NR43] & 0xF0) && !(gb->io_registers[GB_IO_NR43] & 0x07)) {
gb->apu.noise_channel.counter_countdown += 1;
}
}
gb->apu.noise_channel.current_volume = gb->io_registers[GB_IO_NR42] >> 4;