git.y1.nz

commit ad54dc57b06c451206cadca05d7b2b943c178d7e
parent 5c1b89e82d9fe5f62bb3c5dae5f1403f3077c450
Author: Lior Halphon <LIJI32@gmail.com>
Date:   Sun, 21 Mar 2021 15:15:04 +0200

Improved time syncing when turning the LCD on and off, fixes #193

Diffstat:
M
Core/memory.c
1
+
M
Core/timing.c
7
++++++-

2 files changed, 7 insertions(+), 1 deletion(-)
diff --git a/Core/memory.c b/Core/memory.c
@@ -919,6 +919,7 @@ static void write_high_memory(GB_gameboy_t *gb, uint16_t addr, uint8_t value)
                     else if (gb->frame_skip_state == GB_FRAMESKIP_SECOND_FRAME_RENDERED) {
                         gb->frame_skip_state = GB_FRAMESKIP_LCD_TURNED_ON;
                     }
+                    GB_timing_sync(gb);
                 }
                 else if (!(value & 0x80) && (gb->io_registers[GB_IO_LCDC] & 0x80)) {
                     /* Sync after turning off LCD */
diff --git a/Core/timing.c b/Core/timing.c
@@ -64,11 +64,16 @@ void GB_timing_sync(GB_gameboy_t *gb)
     uint64_t target_nanoseconds = gb->cycles_since_last_sync * 1000000000LL / 2 / GB_get_clock_rate(gb); /* / 2 because we use 8MHz units */
     int64_t nanoseconds = get_nanoseconds();
     int64_t time_to_sleep = target_nanoseconds + gb->last_sync - nanoseconds;
-    if (time_to_sleep > 0 && time_to_sleep < LCDC_PERIOD * 1000000000LL / GB_get_clock_rate(gb)) {
+    if (time_to_sleep > 0 && time_to_sleep < LCDC_PERIOD * 1200000000LL / GB_get_clock_rate(gb)) { // +20% to be more forgiving
         nsleep(time_to_sleep);
         gb->last_sync += target_nanoseconds;
     }
     else {
+        if (-time_to_sleep < LCDC_PERIOD * 1200000000LL / GB_get_clock_rate(gb)) {
+            // We're running a bit too slow, but the difference is small enough,
+            // just skip this sync and let it even out
+            return;
+        }
         gb->last_sync = nanoseconds;
     }
 

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