From 0577aa3569f3ad303e62038415dbd93210ae0063 Mon Sep 17 00:00:00 2001
From: tildearrow <tildearrow@protonmail.com>
Date: Thu, 26 May 2022 19:00:14 -0500
Subject: [PATCH] SMS: early Nuked-PSG modding

---
 extern/Nuked-PSG/ympsg.c    | 8 +++++---
 extern/Nuked-PSG/ympsg.h    | 4 +++-
 src/engine/platform/sms.cpp | 2 +-
 3 files changed, 9 insertions(+), 5 deletions(-)

diff --git a/extern/Nuked-PSG/ympsg.c b/extern/Nuked-PSG/ympsg.c
index 8c1715ec..f6b8247b 100644
--- a/extern/Nuked-PSG/ympsg.c
+++ b/extern/Nuked-PSG/ympsg.c
@@ -125,10 +125,10 @@ static void YMPSG_ClockInternal1(ympsg_t *chip)
     }
     else if (noise_of && !chip->noise_of)
     {
-        noise_bit1 = (chip->noise >> 15) & 1;
+        noise_bit1 = (chip->noise >> chip->noise_tap2) & 1;
         noise_bit2 = (chip->noise >> 12) & 1;
         noise_bit1 ^= noise_bit2;
-        noise_next = ((noise_bit1 && ((chip->noise_data >> 2) & 1)) || ((chip->noise & 32767) == 0));
+        noise_next = ((noise_bit1 && ((chip->noise_data >> 2) & 1)) || ((chip->noise & chip->noise_size) == 0));
         chip->noise <<= 1;
         chip->noise |= noise_next;
     }
@@ -253,11 +253,13 @@ uint16_t YMPSG_Read(ympsg_t *chip)
     return data;
 }
 
-void YMPSG_Init(ympsg_t *chip)
+void YMPSG_Init(ympsg_t *chip, uint8_t real_sn)
 {
     uint32_t i;
     memset(chip, 0, sizeof(ympsg_t));
     YMPSG_SetIC(chip, 1);
+    chip->noise_tap2 = real_sn ? 13 : 15;
+    chip->noise_size = real_sn ? 16383 : 32767;
     for (i = 0; i < 16; i++)
     {
         YMPSG_Clock(chip);
diff --git a/extern/Nuked-PSG/ympsg.h b/extern/Nuked-PSG/ympsg.h
index f1596214..06310580 100644
--- a/extern/Nuked-PSG/ympsg.h
+++ b/extern/Nuked-PSG/ympsg.h
@@ -46,6 +46,8 @@ typedef struct {
     uint8_t sign_l;
     uint8_t noise_sign_l;
     uint16_t noise;
+    uint8_t noise_tap2;
+    uint16_t noise_size;
     uint8_t test;
     uint8_t volume_out[4];
 
@@ -62,7 +64,7 @@ typedef struct {
 
 void YMPSG_Write(ympsg_t *chip, uint8_t data);
 uint16_t YMPSG_Read(ympsg_t *chip);
-void YMPSG_Init(ympsg_t *chip);
+void YMPSG_Init(ympsg_t *chip, uint8_t real_sn);
 void YMPSG_SetIC(ympsg_t *chip, uint32_t ic);
 void YMPSG_Clock(ympsg_t *chip);
 float YMPSG_GetOutput(ympsg_t *chip);
diff --git a/src/engine/platform/sms.cpp b/src/engine/platform/sms.cpp
index 302317e9..c0dd9ed5 100644
--- a/src/engine/platform/sms.cpp
+++ b/src/engine/platform/sms.cpp
@@ -358,7 +358,7 @@ void DivPlatformSMS::reset() {
     addWrite(0xffffffff,0);
   }
   sn->device_start();
-  YMPSG_Init(&sn_nuked);
+  YMPSG_Init(&sn_nuked,isRealSN);
   snNoiseMode=3;
   rWrite(0xe7);
   updateSNMode=false;