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Improved accuracy of mid-line SCX writes

This commit is contained in:
Lior Halphon 2021-10-08 19:29:43 +03:00
parent d4999fbbdb
commit c05c3c2abd
4 changed files with 8 additions and 12 deletions
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14
Core/display.c
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@ -632,7 +632,7 @@ static void advance_fetcher_state_machine(GB_gameboy_t *gb)
GB_FETCHER_SLEEP,
} fetcher_step_t;
fetcher_step_t fetcher_state_machine [8] = {
static const fetcher_step_t fetcher_state_machine [8] = {
GB_FETCHER_SLEEP,
GB_FETCHER_GET_TILE,
GB_FETCHER_SLEEP,
@ -666,7 +666,10 @@ static void advance_fetcher_state_machine(GB_gameboy_t *gb)
x = gb->window_tile_x;
}
else {
x = ((gb->io_registers[GB_IO_SCX] / 8) + gb->fetcher_x) & 0x1F;
/* TODO: There is some CGB timing error around here.
Adjusting SCX by 7 or less shouldn't have an effect on a CGB,
but SameBoy is affected by a change of both 7 and 6 (but not less). */
x = ((gb->io_registers[GB_IO_SCX] + gb->position_in_line + 8) / 8) & 0x1F;
}
if (gb->model > GB_MODEL_CGB_C) {
/* This value is cached on the CGB-D and newer, so it cannot be used to mix tiles together */
@ -777,12 +780,6 @@ static void advance_fetcher_state_machine(GB_gameboy_t *gb)
// fallthrough
case GB_FETCHER_PUSH: {
if (gb->fetcher_state == 6) {
/* The background map index increase at this specific point. If this state is not reached,
it will simply not increase. */
gb->fetcher_x++;
gb->fetcher_x &= 0x1f;
}
if (gb->fetcher_state < 7) {
gb->fetcher_state++;
}
@ -1049,7 +1046,6 @@ void GB_display_run(GB_gameboy_t *gb, uint8_t cycles)
gb->position_in_line = - (gb->io_registers[GB_IO_SCX] & 7) - 8;
gb->lcd_x = 0;
gb->fetcher_x = 0;
gb->extra_penalty_for_sprite_at_0 = (gb->io_registers[GB_IO_SCX] & 7);

2
Core/gb.h
View File

@ -581,7 +581,7 @@ struct GB_gameboy_internal_s {
uint8_t current_line;
uint16_t ly_for_comparison;
GB_fifo_t bg_fifo, oam_fifo;
uint8_t fetcher_x;
GB_PADDING(uint8_t, fetcher_x);
uint8_t fetcher_y;
uint16_t cycles_for_line;
uint8_t current_tile;

1
Core/save_state.c
View File

@ -348,7 +348,6 @@ static void sanitize_state(GB_gameboy_t *gb)
gb->oam_fifo.read_end &= 0xF;
gb->oam_fifo.write_end &= 0xF;
gb->object_low_line_address &= gb->vram_size & ~1;
gb->fetcher_x &= 0x1f;
if (gb->lcd_x > gb->position_in_line) {
gb->lcd_x = gb->position_in_line;
}

3
Core/sm83_cpu.c
View File

@ -35,7 +35,8 @@ static const GB_conflict_t cgb_conflict_map[0x80] = {
[GB_IO_OBP0] = GB_CONFLICT_PALETTE_CGB,
[GB_IO_OBP1] = GB_CONFLICT_PALETTE_CGB,
[GB_IO_NR10] = GB_CONFLICT_NR10,
[GB_IO_SCX] = GB_CONFLICT_WRITE_CPU, // TODO: Similar to BGP, there's some time travelling involved
/* Todo: most values not verified, and probably differ between revisions */
};