From 7bc3166ed5eac383364595541c966a6ca14fe337 Mon Sep 17 00:00:00 2001
From: tildearrow <tildearrow@protonmail.com>
Date: Fri, 22 Jul 2022 00:01:29 -0500
Subject: [PATCH] YMZ280B: frequency precision improvement

frequency is now multiplied by 256 and then fed to the chip divided by
256 to increase freq precision
---
 src/engine/platform/ymz280b.cpp | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/src/engine/platform/ymz280b.cpp b/src/engine/platform/ymz280b.cpp
index 87193da5..b690d30c 100644
--- a/src/engine/platform/ymz280b.cpp
+++ b/src/engine/platform/ymz280b.cpp
@@ -23,7 +23,7 @@
 #include <math.h>
 #include <map>
 
-#define CHIP_FREQBASE 98304
+#define CHIP_FREQBASE 25165824
 
 #define rWrite(a,v) {if(!skipRegisterWrites) {ymz280b.write(0,a); ymz280b.write(1,v); regPool[a]=v; if(dumpWrites) addWrite(a,v); }}
 
@@ -142,7 +142,7 @@ void DivPlatformYMZ280B::tick(bool sysTick) {
         default: ctrl=0;
       }
       double off=(s->centerRate>=1)?((double)s->centerRate/8363.0):1.0;
-      chan[i].freq=(int)(off*parent->calcFreq(chan[i].baseFreq,chan[i].pitch,false,2,chan[i].pitch2,chipClock,CHIP_FREQBASE))-1;
+      chan[i].freq=(int)round(off*parent->calcFreq(chan[i].baseFreq,chan[i].pitch,false,2,chan[i].pitch2,chipClock,CHIP_FREQBASE)/256.0)-1;
       if (chan[i].freq<0) chan[i].freq=0;
       if (chan[i].freq>511) chan[i].freq=511;
       // ADPCM has half the range
@@ -267,14 +267,15 @@ int DivPlatformYMZ280B::dispatch(DivCommand c) {
     case DIV_CMD_NOTE_PORTA: {
       int destFreq=NOTE_FREQUENCY(c.value2);
       bool return2=false;
+      int multiplier=(parent->song.linearPitch==2)?1:256;
       if (destFreq>chan[c.chan].baseFreq) {
-        chan[c.chan].baseFreq+=c.value;
+        chan[c.chan].baseFreq+=c.value*multiplier;
         if (chan[c.chan].baseFreq>=destFreq) {
           chan[c.chan].baseFreq=destFreq;
           return2=true;
         }
       } else {
-        chan[c.chan].baseFreq-=c.value;
+        chan[c.chan].baseFreq-=c.value*multiplier;
         if (chan[c.chan].baseFreq<=destFreq) {
           chan[c.chan].baseFreq=destFreq;
           return2=true;