From 0c5e58fa3e0f4328d534821ed9bd5e2a23c617b0 Mon Sep 17 00:00:00 2001
From: tildearrow <me@tildearrow.org>
Date: Sun, 9 Jul 2023 15:12:45 -0500
Subject: [PATCH] YM2612: implement 9xxx, part 1

does not work on VGM export yet
---
 src/engine/dispatch.h           |  3 +++
 src/engine/platform/genesis.cpp | 15 ++++++++++++---
 src/engine/platform/genesis.h   |  2 ++
 3 files changed, 17 insertions(+), 3 deletions(-)

diff --git a/src/engine/dispatch.h b/src/engine/dispatch.h
index c458cf9c..acb7af66 100644
--- a/src/engine/dispatch.h
+++ b/src/engine/dispatch.h
@@ -288,6 +288,9 @@ struct DivRegWrite {
    *   - x is the instance ID
    * - 0xffffxx04: switch sample bank
    *   - for use in VGM export
+   * - 0xffffxx05: set sample position
+   *   - xx is the instance ID
+   *   - data is the sample position
    * - 0xffffffff: reset
    */
   unsigned int addr;
diff --git a/src/engine/platform/genesis.cpp b/src/engine/platform/genesis.cpp
index 1933a057..36284160 100644
--- a/src/engine/platform/genesis.cpp
+++ b/src/engine/platform/genesis.cpp
@@ -63,7 +63,7 @@ void DivPlatformGenesis::processDAC(int iRate) {
       for (int i=5; i<7; i++) {
         if (chan[i].dacSample!=-1) {
           DivSample* s=parent->getSample(chan[i].dacSample);
-          if (!isMuted[i] && s->samples>0) {
+          if (!isMuted[i] && s->samples>0 && chan[i].dacPos<s->samples) {
             if (parent->song.noOPN2Vol) {
               chan[i].dacOutput=s->data8[chan[i].dacDirection?(s->samples-chan[i].dacPos-1):chan[i].dacPos];
             } else {
@@ -110,7 +110,7 @@ void DivPlatformGenesis::processDAC(int iRate) {
       chan[5].dacPeriod+=chan[5].dacRate;
       if (chan[5].dacPeriod>=iRate) {
         DivSample* s=parent->getSample(chan[5].dacSample);
-        if (s->samples>0) {
+        if (s->samples>0 && chan[5].dacPos<s->samples) {
           if (!isMuted[5]) {
             if (chan[5].dacReady && writes.size()<16) {
               int sample;
@@ -701,7 +701,11 @@ int DivPlatformGenesis::dispatch(DivCommand c) {
               addWrite(0xffff0003,chan[c.chan].dacDirection);
             }
           }
-          chan[c.chan].dacPos=0;
+          if (chan[c.chan].setPos) {
+            chan[c.chan].setPos=false;
+          } else {
+            chan[c.chan].dacPos=0;
+          }
           chan[c.chan].dacPeriod=0;
           if (c.value!=DIV_NOTE_NULL) {
             chan[c.chan].baseFreq=parent->calcBaseFreq(1,1,c.value,false);
@@ -924,6 +928,11 @@ int DivPlatformGenesis::dispatch(DivCommand c) {
       if (dumpWrites) addWrite(0xffff0003,chan[c.chan].dacDirection);
       break;
     }
+    case DIV_CMD_SAMPLE_POS:
+      if (c.chan<5) c.chan=5;
+      chan[c.chan].dacPos=c.value;
+      chan[c.chan].setPos=true;
+      break;
     case DIV_CMD_LEGATO: {
       if (c.chan==csmChan) {
         chan[c.chan].baseFreq=NOTE_PERIODIC(c.value);
diff --git a/src/engine/platform/genesis.h b/src/engine/platform/genesis.h
index 210fca9d..c9de0493 100644
--- a/src/engine/platform/genesis.h
+++ b/src/engine/platform/genesis.h
@@ -57,6 +57,7 @@ class DivPlatformGenesis: public DivPlatformOPN {
       int dacDelay;
       bool dacReady;
       bool dacDirection;
+      bool setPos;
       unsigned char sampleBank;
       signed char dacOutput;
       Channel():
@@ -70,6 +71,7 @@ class DivPlatformGenesis: public DivPlatformOPN {
         dacDelay(0),
         dacReady(true),
         dacDirection(false),
+        setPos(false),
         sampleBank(0),
         dacOutput(0) {}
     };