AUDIO: Add easy way to write to OPL3's secondary register set.

1 files changed, 21 insertions, 6 deletions

diff --git a/audio/softsynth/opl/dosbox.cpp b/audio/softsynth/opl/dosbox.cpp
index e039845b8f..a1a736f9de 100644
--- a/audio/softsynth/opl/dosbox.cpp
+++ b/audio/softsynth/opl/dosbox.cpp
@@ -247,7 +247,7 @@ byte OPL::read(int port) {
 }
 
 void OPL::writeReg(int r, int v) {
-	byte tempReg = 0;
+	int tempReg = 0;
 	switch (_type) {
 	case Config::kOpl2:
 	case Config::kDualOpl2:
@@ -257,12 +257,27 @@ void OPL::writeReg(int r, int v) {
 		// Backup old setup register
 		tempReg = _reg.normal;
 
-		// We need to set the register we want to write to via port 0x388
-		write(0x388, r);
-		// Do the real writing to the register
-		write(0x389, v);
+		// We directly allow writing to secondary OPL3 registers by using
+		// register values >= 0x100.
+		if (_type == Config::kOpl3 && r >= 0x100) {
+			// We need to set the register we want to write to via port 0x222,
+			// since we want to write to the secondary register set.
+			write(0x222, r);
+			// Do the real writing to the register
+			write(0x223, v);
+		} else {
+			// We need to set the register we want to write to via port 0x388
+			write(0x388, r);
+			// Do the real writing to the register
+			write(0x389, v);
+		}
+
 		// Restore the old register
-		write(0x388, tempReg);
+		if (_type == Config::kOpl3 && tempReg >= 0x100) {
+			write(0x222, tempReg & ~0x100);
+		} else {
+			write(0x388, tempReg);
+		}
 		break;
 	};
 }