git.y1.nz

commit 9450eb9575b8fbf7ff22efbcac473fc3a8c4d91a
parent 9c23f0d685dcac856d9b3520a4f9894710442bad
Author: Lior Halphon <LIJI32@gmail.com>
Date:   Mon, 16 Feb 2026 01:10:07 +0200

Fix timing inaccuracy

Diffstat:
M
Core/apu.c
17
+++++++++++------

1 file changed, 11 insertions(+), 6 deletions(-)
diff --git a/Core/apu.c b/Core/apu.c
@@ -1248,14 +1248,19 @@ static void prepare_noise_start(GB_gameboy_t *gb)
             divisor = 8;
         }
         else if (divisor == 1) {
-            /* TODO: I'm not 100% sure this only affects NR43 = 1X */
-            if ((gb->io_registers[GB_IO_NR43] & 0xf0) == 0x10 && (gb->apu.noise_channel.counter & 1)) {
-                instant_step = true;
-            }
-            /* TODO: needs further research, the conditions are very odd. What if NR43 changes before stepping? */
-            if ((gb->io_registers[GB_IO_NR43] & 0xf0) == 0x10 && !gb->apu.noise_channel.did_step_counter) {
+            if (!gb->apu.noise_channel.did_step_counter) {
                 div_1_glitch = true;
             }
+            
+            uint16_t mask = 1 << (gb->io_registers[GB_IO_NR43] >> 4);
+            bool old_bit = gb->apu.noise_channel.counter & mask;
+            gb->apu.noise_channel.counter++;
+            gb->apu.noise_channel.counter &= 0x3FFF;
+            bool new_bit = gb->apu.noise_channel.counter & mask;
+            
+            if ((new_bit && !old_bit)) {
+                instant_step = true;
+            }
         }
     }
     gb->apu.noise_channel.counter_countdown = divisor == 0? 6 : divisor * 4 + 6;

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