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gb6
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bad timer implementation

This commit is contained in:
Matthew Laux 2022-08-04 01:57:14 -05:00
parent af18bb9a39
commit 03dab9524b
2 changed files with 35 additions and 2 deletions
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29
src/dmg.c
View File

@ -81,7 +81,7 @@ u8 dmg_read(void *_dmg, u16 address)
return dmg->zero_page[address - 0xff80];
} else if (address == 0xff00) {
return get_button_state(dmg);
} else if (address == 0xff04) {
} else if (address == REG_TIMER_DIV) {
counter++;
return counter;
} else if (address == 0xff0f) {
@ -246,6 +246,31 @@ static void render_objs(struct dmg *dmg)
}
}
static void timer_step(struct dmg *dmg)
{
if (!(dmg_read(dmg, REG_TIMER_CONTROL) & TIMER_CONTROL_ENABLED)) {
return;
}
int passed = dmg->cpu->cycle_count - dmg->last_timer_update;
// TODO
if (passed < 10000) {
return;
}
u8 counter = dmg_read(dmg, REG_TIMER_COUNT);
u8 modulo = dmg_read(dmg, REG_TIMER_MOD);
counter++;
if (!counter) {
counter = modulo;
dmg_request_interrupt(dmg, INT_TIMER);
}
dmg_write(dmg, REG_TIMER_COUNT, counter);
dmg->last_timer_update = dmg->cpu->cycle_count;
}
void dmg_step(void *_dmg)
{
struct dmg *dmg = (struct dmg *) _dmg;
@ -253,9 +278,9 @@ void dmg_step(void *_dmg)
// order of dependencies? i think cpu needs to step first then update
// all other hw
cpu_step(dmg->cpu);
timer_step(dmg);
// each line takes 456 cycles
int cycle_diff = dmg->cpu->cycle_count - dmg->last_lcd_update;
if (cycle_diff >= 456) {

8
src/dmg.h
View File

@ -15,6 +15,13 @@
#define BUTTON_SELECT (1 << 2)
#define BUTTON_START (1 << 3)
#define REG_TIMER_DIV 0xFF04
#define REG_TIMER_COUNT 0xFF05
#define REG_TIMER_MOD 0xFF06
#define REG_TIMER_CONTROL 0xFF07
#define TIMER_CONTROL_ENABLED (1 << 2)
struct cpu;
struct rom;
struct lcd;
@ -27,6 +34,7 @@ struct dmg {
u8 video_ram[0x2000];
u8 zero_page[0x80];
u32 last_lcd_update;
u32 last_timer_update;
int joypad_selected;
int action_selected; // non-0 if A/B/start/select selected, 0 for directions
u8 interrupt_enabled;