From 86d6fb9a2f232c8e83ebdcdae5357cf3fa66d565 Mon Sep 17 00:00:00 2001
From: kub <derkub@gmail.com>
Date: Sat, 2 Oct 2021 09:32:57 +0200
Subject: [PATCH] sound, increase resolution for calculating psg sound

---
 pico/memory.c      |  7 ++-----
 pico/pico_int.h    |  6 +++---
 pico/sound/sound.c | 36 ++++++++++++++++++++++--------------
 3 files changed, 27 insertions(+), 22 deletions(-)

diff --git a/pico/memory.c b/pico/memory.c
index 25e78310..04875465 100644
--- a/pico/memory.c
+++ b/pico/memory.c
@@ -394,13 +394,11 @@ void NOINLINE ctl_write_z80reset(u32 d)
   }
 }
 
-static int get_scanline(int is_from_z80);
-
 static void psg_write_68k(u32 d)
 {
   // look for volume write and update if needed
   if ((d & 0x90) == 0x90)
-    PsndDoPSG(Pico.m.scanline);
+    PsndDoPSG(z80_cycles_from_68k());
 
   SN76496Write(d);
 }
@@ -408,8 +406,7 @@ static void psg_write_68k(u32 d)
 static void psg_write_z80(u32 d)
 {
   if ((d & 0x90) == 0x90) {
-    int scanline = get_scanline(1);
-    PsndDoPSG(scanline);
+    PsndDoPSG(z80_cyclesDone());
   }
 
   SN76496Write(d);
diff --git a/pico/pico_int.h b/pico/pico_int.h
index 2038b6d9..f4dcef3c 100644
--- a/pico/pico_int.h
+++ b/pico/pico_int.h
@@ -914,9 +914,9 @@ PICO_INTERNAL void PsndExit(void);
 PICO_INTERNAL void PsndReset(void);
 PICO_INTERNAL void PsndStartFrame(void);
 PICO_INTERNAL void PsndDoDAC(int cycle_to);
-PICO_INTERNAL void PsndDoPSG(int line_to);
-PICO_INTERNAL void PsndDoYM2413(int line_to);
-PICO_INTERNAL void PsndDoFM(int line_to);
+PICO_INTERNAL void PsndDoPSG(int cyc_to);
+PICO_INTERNAL void PsndDoYM2413(int cyc_to);
+PICO_INTERNAL void PsndDoFM(int cyc_to);
 PICO_INTERNAL void PsndClear(void);
 PICO_INTERNAL void PsndGetSamples(int y);
 PICO_INTERNAL void PsndGetSamplesMS(int y);
diff --git a/pico/sound/sound.c b/pico/sound/sound.c
index 5cb6832e..69cd4fb3 100644
--- a/pico/sound/sound.c
+++ b/pico/sound/sound.c
@@ -161,20 +161,24 @@ PICO_INTERNAL void PsndDoDAC(int cyc_to)
   Pico.snd.dac_val = dout;
 }
 
-PICO_INTERNAL void PsndDoPSG(int line_to)
+PICO_INTERNAL void PsndDoPSG(int cyc_to)
 {
   int pos, len;
   int stereo = 0;
 
-  // Q16, number of samples since last call
-  len = ((line_to+1) * Pico.snd.smpl_mult) - Pico.snd.psg_pos;
-  if (len <= 0)
-    return;
+  // number of samples to fill in buffer (Q20)
+  len = (cyc_to * Pico.snd.clkl_mult) - Pico.snd.psg_pos;
 
   // update position and calculate buffer offset and length
-  pos = (Pico.snd.psg_pos+0x8000) >> 16;
+  pos = (Pico.snd.psg_pos+0x80000) >> 20;
   Pico.snd.psg_pos += len;
-  len = ((Pico.snd.psg_pos+0x8000) >> 16) - pos;
+  len = ((Pico.snd.psg_pos+0x80000) >> 20) - pos;
+
+  // avoid loss of the 1st sample of a new block (Q rounding issues)
+  if (pos+len == 0)
+    len = 1, Pico.snd.psg_pos += 0x80000;
+  if (len <= 0)
+    return;
 
   if (!PicoIn.sndOut || !(PicoIn.opt & POPT_EN_PSG))
     return;
@@ -187,21 +191,25 @@ PICO_INTERNAL void PsndDoPSG(int line_to)
 }
 
 #if 0
-PICO_INTERNAL void PsndDoYM2413(int line_to)
+PICO_INTERNAL void PsndDoYM2413(int cyc_to)
 {
   int pos, len;
   int stereo = 0;
   short *buf;
 
-  // Q16, number of samples since last call
-  len = ((line_to+1) * Pico.snd.smpl_mult) - Pico.snd.ym2413_pos;
-  if (len <= 0)
-    return;
+  // number of samples to fill in buffer (Q20)
+  len = (cyc_to * Pico.snd.clkl_mult) - Pico.snd.ym2413_pos;
 
   // update position and calculate buffer offset and length
-  pos = (Pico.snd.ym2413_pos+0x8000) >> 16;
+  pos = (Pico.snd.ym2413_pos+0x80000) >> 20;
   Pico.snd.ym2413_pos += len;
-  len = ((Pico.snd.ym2413_pos+0x8000) >> 16) - pos;
+  len = ((Pico.snd.ym2413_pos+0x80000) >> 20) - pos;
+
+  // avoid loss of the 1st sample of a new block (Q rounding issues)
+  if (pos+len == 0)
+    len = 1, Pico.snd.ym2413_pos += 0x80000;
+  if (len <= 0)
+    return;
 
   if (!PicoIn.sndOut || !(PicoIn.opt & POPT_EN_YM2413))
     return;
-- 
2.39.5