From 54687cde58d72ed965d2de5121a7fcabfbbb88d0 Mon Sep 17 00:00:00 2001
From: EkeEke <ekeeke31@gmail.com>
Date: Mon, 15 Oct 2012 10:40:39 +0200
Subject: [PATCH] .fixed broken PSG noise frequency .improved accuracy Game
 Gear PSG stereo (cycle-accurate)

---
 source/io_ctrl.c       |  2 +-
 source/sound/sn76489.c | 58 +++++++++++++++++++++++++-----------------
 source/sound/sn76489.h |  2 +-
 source/sound/sound.c   |  2 +-
 source/state.c         |  4 +--
 5 files changed, 39 insertions(+), 29 deletions(-)

diff --git a/source/io_ctrl.c b/source/io_ctrl.c
index a8642a5..2b4f924 100644
--- a/source/io_ctrl.c
+++ b/source/io_ctrl.c
@@ -547,7 +547,7 @@ void io_gg_write(unsigned int offset, unsigned int data)
 
     case 6: /* PSG Stereo output control */
       io_reg[6] = data;
-      SN76489_Config(config.psg_preamp, config.psgBoostNoise, data);
+      SN76489_Config(Z80.cycles, config.psg_preamp, config.psgBoostNoise, data);
       return;
 
     default: /* Read-only */
diff --git a/source/sound/sn76489.c b/source/sound/sn76489.c
index b507ac6..bcba8cb 100644
--- a/source/sound/sn76489.c
+++ b/source/sound/sn76489.c
@@ -157,29 +157,6 @@ void SN76489_Reset()
   SN76489.clocks = 0;
 }
 
-void SN76489_Config(int preAmp, int boostNoise, int stereo)
-{
-  int i;
-
-  for (i=0; i<4; i++)
-  {
-    /* stereo channel pre-amplification */
-    SN76489.PreAmp[i][0] = preAmp * ((stereo >> (i*2)) & 1);
-    SN76489.PreAmp[i][1] = preAmp * ((stereo >> (i*2 + 1)) & 1);
-
-    /* noise channel boost */
-    if (i == 3)
-    {
-      SN76489.PreAmp[3][0] = SN76489.PreAmp[3][0] << boostNoise;
-      SN76489.PreAmp[3][1] = SN76489.PreAmp[3][1] << boostNoise;
-    }
-
-    /* update stereo channel amplitude */
-    SN76489.Channel[i][0]= (PSGVolumeValues[SN76489.Registers[i*2 + 1]] * SN76489.PreAmp[i][0]) / 100;
-    SN76489.Channel[i][1]= (PSGVolumeValues[SN76489.Registers[i*2 + 1]] * SN76489.PreAmp[i][1]) / 100;
-  }
-}
-
 void *SN76489_GetContextPtr(void)
 {
   return (uint8 *)&SN76489;
@@ -331,6 +308,39 @@ static void SN76489_RunUntil(unsigned int clocks)
   }
 }
 
+void SN76489_Config(unsigned int clocks, int preAmp, int boostNoise, int stereo)
+{
+  int i;
+
+  /* cycle-accurate Game Gear stereo */
+  if (clocks > SN76489.clocks)
+  {
+    /* Run chip until current timestamp */
+    SN76489_RunUntil(clocks);
+
+    /* Update internal M-cycle counter */
+    SN76489.clocks += ((clocks - SN76489.clocks + PSG_MCYCLES_RATIO - 1) / PSG_MCYCLES_RATIO) * PSG_MCYCLES_RATIO;
+  }
+
+  for (i=0; i<4; i++)
+  {
+    /* stereo channel pre-amplification */
+    SN76489.PreAmp[i][0] = preAmp * ((stereo >> (i*2)) & 1);
+    SN76489.PreAmp[i][1] = preAmp * ((stereo >> (i*2 + 1)) & 1);
+
+    /* noise channel boost */
+    if (i == 3)
+    {
+      SN76489.PreAmp[3][0] = SN76489.PreAmp[3][0] << boostNoise;
+      SN76489.PreAmp[3][1] = SN76489.PreAmp[3][1] << boostNoise;
+    }
+
+    /* update stereo channel amplitude */
+    SN76489.Channel[i][0]= (PSGVolumeValues[SN76489.Registers[i*2 + 1]] * SN76489.PreAmp[i][0]) / 100;
+    SN76489.Channel[i][1]= (PSGVolumeValues[SN76489.Registers[i*2 + 1]] * SN76489.PreAmp[i][1]) / 100;
+  }
+}
+
 void SN76489_Update(unsigned int clocks)
 {
   int i;
@@ -424,7 +434,7 @@ void SN76489_Write(unsigned int clocks, unsigned int data)
       SN76489.NoiseShiftRegister = NoiseInitialState;
 
       /* set noise signal generator frequency */
-      SN76489.NoiseFreq = (0x10 << (data&0x3)) * PSG_MCYCLES_RATIO;
+      SN76489.NoiseFreq = 0x10 << (data&0x3);
       break;
     }
 
diff --git a/source/sound/sn76489.h b/source/sound/sn76489.h
index 3c59611..19d4a86 100644
--- a/source/sound/sn76489.h
+++ b/source/sound/sn76489.h
@@ -14,7 +14,7 @@
 /* Function prototypes */
 extern void SN76489_Init(blip_t* left, blip_t* right, int type);
 extern void SN76489_Reset(void);
-extern void SN76489_Config(int preAmp, int boostNoise, int stereo);
+extern void SN76489_Config(unsigned int clocks, int preAmp, int boostNoise, int stereo);
 extern void SN76489_Write(unsigned int clocks, unsigned int data);
 extern void SN76489_Update(unsigned int cycles);
 extern void *SN76489_GetContextPtr(void);
diff --git a/source/sound/sound.c b/source/sound/sound.c
index d36d349..868c2cf 100644
--- a/source/sound/sound.c
+++ b/source/sound/sound.c
@@ -102,7 +102,7 @@ void sound_init( void )
   }
 
   /* Initialize PSG chip */
-  SN76489_Config(config.psg_preamp, config.psgBoostNoise, 0xff);
+  SN76489_Config(0, config.psg_preamp, config.psgBoostNoise, 0xff);
 }
 
 void sound_reset(void)
diff --git a/source/state.c b/source/state.c
index 7ee3fb9..e5b75f6 100644
--- a/source/state.c
+++ b/source/state.c
@@ -117,12 +117,12 @@ int state_load(unsigned char *state)
   if ((system_hw & SYSTEM_PBC) == SYSTEM_MD)
   {
     SN76489_Init(snd.blips[0][0], snd.blips[0][1], SN_INTEGRATED);
-    SN76489_Config(config.psg_preamp, config.psgBoostNoise, 0xff);
+    SN76489_Config(0, config.psg_preamp, config.psgBoostNoise, 0xff);
   }
   else
   {
     SN76489_Init(snd.blips[0][0], snd.blips[0][1], (system_hw < SYSTEM_MARKIII) ? SN_DISCRETE : SN_INTEGRATED);
-    SN76489_Config(config.psg_preamp, config.psgBoostNoise, io_reg[6]);
+    SN76489_Config(0, config.psg_preamp, config.psgBoostNoise, io_reg[6]);
   }
 
   /* 68000 */