From 423d9fa45d07a3b24f7cffc4ee91aa7c5a068e59 Mon Sep 17 00:00:00 2001
From: tildearrow <tildearrow@protonmail.com>
Date: Sat, 12 Feb 2022 17:43:30 -0500
Subject: [PATCH] Amiga: early bus limits emulation

it appears that if the period is lower than 124, the positions start
to desync

this is emulated by UAE, but i am not sure whether this happens on a real machine
and this isn't emulated properly here either
---
 src/engine/platform/amiga.cpp | 12 +++++++++---
 src/engine/platform/amiga.h   |  2 ++
 2 files changed, 11 insertions(+), 3 deletions(-)

diff --git a/src/engine/platform/amiga.cpp b/src/engine/platform/amiga.cpp
index 82a21813..c2a9d0f7 100644
--- a/src/engine/platform/amiga.cpp
+++ b/src/engine/platform/amiga.cpp
@@ -69,9 +69,15 @@ void DivPlatformAmiga::acquire(short* bufL, short* bufR, size_t start, size_t le
           } else {
             chan[i].sample=-1;
           }
-          /*if (chan[i].freq<124) {
-            // ???
-          }*/
+          if (chan[i].freq<124) {
+            if (++chan[i].busClock>=512) {
+              unsigned int rAmount=(124-chan[i].freq)*2;
+              if (chan[i].audPos>=rAmount) {
+                chan[i].audPos-=rAmount;
+              }
+              chan[i].busClock=0;
+            }
+          }
           chan[i].audSub+=MAX(114,chan[i].freq);
         }
       }
diff --git a/src/engine/platform/amiga.h b/src/engine/platform/amiga.h
index 7dba475e..c37a8d65 100644
--- a/src/engine/platform/amiga.h
+++ b/src/engine/platform/amiga.h
@@ -15,6 +15,7 @@ class DivPlatformAmiga: public DivDispatch {
     signed char audDat;
     int sample, wave;
     unsigned char ins;
+    int busClock;
     int note;
     bool active, insChanged, freqChanged, keyOn, keyOff, inPorta, useWave;
     signed char vol, outVol;
@@ -31,6 +32,7 @@ class DivPlatformAmiga: public DivDispatch {
       sample(-1),
       wave(0),
       ins(-1),
+      busClock(0),
       note(0),
       active(false),
       insChanged(true),