From 0056cc2d61448e9b3842f27449da4b62620f3adc Mon Sep 17 00:00:00 2001
From: Lior Halphon <LIJI32@gmail.com>
Date: Sat, 16 Jan 2021 14:42:13 +0200
Subject: [PATCH] Revert "Further NR43 write glitch emulation" for now

This reverts commit e38470761555007bf5b8e579612962efb0dde402.
---
 Core/apu.c | 48 ++++++++++++++++--------------------------------
 1 file changed, 16 insertions(+), 32 deletions(-)

diff --git a/Core/apu.c b/Core/apu.c
index bd00d499..37065998 100644
--- a/Core/apu.c
+++ b/Core/apu.c
@@ -710,7 +710,7 @@ uint8_t GB_apu_read(GB_gameboy_t *gb, uint8_t reg)
     return gb->io_registers[reg] | read_mask[reg - GB_IO_NR10];
 }
 
-static inline uint16_t effective_channel4_counter(GB_gameboy_t *gb, uint8_t nr43)
+static inline uint16_t effective_channel4_counter(GB_gameboy_t *gb)
 {
     uint16_t effective_counter = gb->apu.noise_channel.counter;
     /* Ladies and gentlemen, I present you the holy grail glitch of revision detection! */
@@ -720,14 +720,7 @@ static inline uint16_t effective_channel4_counter(GB_gameboy_t *gb, uint8_t nr43
 #if 0
         case GB_MODEL_CGB_B:
             if (effective_counter & 8) {
-                // Verify this part
-                if (gb->apu.channel_4_countdown_reloaded && !(effective_counter & 1)) {
-                    uint16_t lower_bits = ~(effective_counter & ~(effective_counter - 1)) & 0xF;
-                    effective_counter = (effective_counter & ~0xF) | lower_bits;
-                }
-                else {
-                    effective_counter |= 0xF;
-                }
+                effective_counter |= 0xE; // Seems to me F under some circumstances?
             }
             if (effective_counter & 0x80) {
                 effective_counter |= 0xFF;
@@ -763,16 +756,7 @@ static inline uint16_t effective_channel4_counter(GB_gameboy_t *gb, uint8_t nr43
             // case GB_MODEL_CGB_A:
         case GB_MODEL_CGB_C:
             if (effective_counter & 8) {
-                if (gb->apu.channel_4_countdown_reloaded && !(effective_counter & 1)) {
-                    uint16_t lower_bits = ~(effective_counter & ~(effective_counter - 1)) & 0xF;
-                    effective_counter = (effective_counter & ~0xF) | lower_bits;
-                    if (!(nr43 >> 4)) {
-                        effective_counter &= ~1;
-                    }
-                }
-                else {
-                    effective_counter |= 0xE;
-                }
+                effective_counter |= 0xE;
             }
             if (effective_counter & 0x80) {
                 effective_counter |= 0xFF;
@@ -836,9 +820,6 @@ static inline uint16_t effective_channel4_counter(GB_gameboy_t *gb, uint8_t nr43
              */
             break;
     }
-    if (gb->model <= GB_MODEL_CGB_C && gb->apu.channel_4_countdown_reloaded && (nr43 >> 4)) {
-        effective_counter = (effective_counter & effective_counter - 1) | (effective_counter & 1);
-    }
     return effective_counter;
 }
 
@@ -1200,22 +1181,16 @@ void GB_apu_write(GB_gameboy_t *gb, uint8_t reg, uint8_t value)
 
         case GB_IO_NR43: {
             gb->apu.noise_channel.narrow = value & 8;
-            uint16_t effective_counter = effective_channel4_counter(gb, value);
+            uint16_t effective_counter = effective_channel4_counter(gb);
             bool old_bit = (effective_counter >> (gb->io_registers[GB_IO_NR43] >> 4)) & 1;
             gb->io_registers[GB_IO_NR43] = value;
             bool new_bit = (effective_counter >> (gb->io_registers[GB_IO_NR43] >> 4)) & 1;
             if (gb->apu.channel_4_countdown_reloaded) {
                 unsigned divisor = (gb->io_registers[GB_IO_NR43] & 0x07) << 2;
                 if (!divisor) divisor = 2;
-                if (gb->model > GB_MODEL_CGB_C) {
-                    gb->apu.noise_channel.counter_countdown =
-                        divisor + (divisor == 2? 0 : (uint8_t[]){2, 1, 0, 3}[(gb->apu.noise_channel.alignment) & 3]);
-                }
-                else {
-                    gb->apu.noise_channel.counter_countdown =
-                        divisor + (divisor == 2? 0 : (uint8_t[]){2, 1, 4, 3}[(gb->apu.noise_channel.alignment) & 3]);
-                }
-                gb->apu.channel_4_delta = 0;
+                 gb->apu.noise_channel.counter_countdown =
+                     divisor + (divisor == 2? 0 : (uint8_t[]){2, 1, 0, 3}[(gb->apu.noise_channel.alignment) & 3]);
+                 gb->apu.channel_4_delta = 0;
             }
             /* Step LFSR */
             if (new_bit && (!old_bit || gb->model <= GB_MODEL_CGB_C)) {
@@ -1263,6 +1238,15 @@ void GB_apu_write(GB_gameboy_t *gb, uint8_t reg, uint8_t value)
                         }
                     }
                     
+                    /* TODO: These two are quite weird. Verify further */
+                    if (gb->model <= GB_MODEL_CGB_C && gb->cgb_double_speed) {
+                        if (!(gb->io_registers[GB_IO_NR43] & 0xF0) && (gb->io_registers[GB_IO_NR43] & 0x07)) {
+                             gb->apu.noise_channel.counter_countdown -= 1;
+                        }
+                        else if ((gb->io_registers[GB_IO_NR43] & 0xF0) && !(gb->io_registers[GB_IO_NR43] & 0x07)) {
+                            gb->apu.noise_channel.counter_countdown += 1;
+                        }
+                    }
    
                     gb->apu.noise_channel.current_volume = gb->io_registers[GB_IO_NR42] >> 4;