From b54a72d9b9a72dc243cd37216b3adb4c99511a44 Mon Sep 17 00:00:00 2001
From: Lior Halphon <LIJI32@gmail.com>
Date: Sat, 2 Jan 2021 14:56:45 +0200
Subject: [PATCH] Fixing a bug where where zero-shift sweep wouldn't tick

---
 Core/apu.c | 7 ++++---
 Core/apu.h | 2 +-
 2 files changed, 5 insertions(+), 4 deletions(-)

diff --git a/Core/apu.c b/Core/apu.c
index 3abca7d..4d66e24 100644
--- a/Core/apu.c
+++ b/Core/apu.c
@@ -394,7 +394,7 @@ static void trigger_sweep_calculation(GB_gameboy_t *gb)
         
         /* Recalculation and overflow check only occurs after a delay */
         gb->apu.square_sweep_calculate_countdown = (gb->io_registers[GB_IO_NR10] & 0x7) * 2 + 5 - gb->apu.lf_div;
-        
+        gb->apu.unshifted_sweep = !(gb->io_registers[GB_IO_NR10] & 0x7);
         gb->apu.square_sweep_countdown = ((gb->io_registers[GB_IO_NR10] >> 4) & 7) ^ 7;
     }
 }
@@ -524,7 +524,7 @@ void GB_apu_run(GB_gameboy_t *gb)
         gb->apu.noise_channel.alignment += cycles;
 
         if (gb->apu.square_sweep_calculate_countdown &&
-            ((gb->io_registers[GB_IO_NR10] & 7) ||
+            (((gb->io_registers[GB_IO_NR10] & 7) || gb->apu.unshifted_sweep) ||
              gb->apu.square_sweep_calculate_countdown <= (gb->model > GB_MODEL_CGB_C? 3 : 1))) { // Calculation is paused if the lower bits
             if (gb->apu.square_sweep_calculate_countdown > cycles) {
                 gb->apu.square_sweep_calculate_countdown -= cycles;
@@ -875,6 +875,7 @@ void GB_apu_write(GB_gameboy_t *gb, uint8_t reg, uint8_t value)
                     if (gb->io_registers[GB_IO_NR10] & 7) {
                         /* APU bug: if shift is nonzero, overflow check also occurs on trigger */
                         gb->apu.square_sweep_calculate_countdown = (gb->io_registers[GB_IO_NR10] & 0x7) * 2 + 5 - gb->apu.lf_div;
+                        gb->apu.unshifted_sweep = false;
                         if (gb->model > GB_MODEL_CGB_C) {
                             gb->apu.square_sweep_calculate_countdown += 2;
                         }
@@ -884,7 +885,7 @@ void GB_apu_write(GB_gameboy_t *gb, uint8_t reg, uint8_t value)
                     else {
                         gb->apu.sweep_length_addend = 0;
                     }
-                    gb->apu.channel_1_restart_hold = 4 - gb->apu.lf_div;
+                    gb->apu.channel_1_restart_hold = 2 - gb->apu.lf_div + GB_is_cgb(gb) * 2;
                     gb->apu.square_sweep_countdown = ((gb->io_registers[GB_IO_NR10] >> 4) & 7) ^ 7;
                 }
             }
diff --git a/Core/apu.h b/Core/apu.h
index 69cea16..eadae1b 100644
--- a/Core/apu.h
+++ b/Core/apu.h
@@ -66,7 +66,7 @@ typedef struct
     uint8_t square_sweep_calculate_countdown; // In 2 MHz
     uint16_t sweep_length_addend;
     uint16_t shadow_sweep_sample_length;
-    GB_PADDING(bool, sweep_enabled);
+    bool unshifted_sweep;
     GB_PADDING(bool, sweep_decreasing);
 
     struct {