prepare for ch3 mode

src/engine/platform/genesisext.cpp

@@ -0,0 +1,32 @@
+#include "genesisext.h"
+#include <math.h>
+
+int DivPlatformGenesisExt::dispatch(DivCommand c) {
+  if (c.chan<2) {
+    return DivPlatformGenesis::dispatch(c);
+  }
+  if (c.chan>5) {
+    c.chan-=3;
+    return DivPlatformGenesis::dispatch(c);
+  }
+  printf("HANDLE: %d %d %d %d\n",c.cmd,c.chan,c.value,c.value2);
+  switch (c.cmd) {
+    case DIV_CMD_NOTE_ON:
+      chan[c.chan].freq=16.4f*pow(2.0f,((float)c.value/12.0f));
+      chan[c.chan].active=true;
+      break;
+    case DIV_CMD_NOTE_OFF:
+      chan[c.chan].active=false;
+      break;
+    case DIV_CMD_VOLUME:
+      chan[c.chan].vol=c.value;
+      break;
+    default:
+      break;
+  }
+  return 1;
+}
+
+void DivPlatformGenesisExt::tick() {
+  DivPlatformGenesis::tick();
+}