M src/gba/gba.c → src/gba/gba.c

@@ -101,6 +101,7 @@ gba->idleLoop = IDLE_LOOP_NONE;
 
 	gba->realisticTiming = true;
 	gba->hardCrash = true;
+	gba->allowOpposingDirections = true;
 
 	gba->performingDMA = false;
 

M src/gba/gba.h → src/gba/gba.h

@@ -128,6 +128,7 @@ bool taintedRegisters[16];
 
 	bool realisticTiming;
 	bool hardCrash;
+	bool allowOpposingDirections;
 };
 
 struct GBACartridge {

M src/gba/io.c → src/gba/io.c

@@ -674,6 +674,17 @@ input = gba->keyCallback->readKeys(gba->keyCallback);
 			} else if (gba->keySource) {
 				input = *gba->keySource;
 			}
+			if (!gba->allowOpposingDirections) {
+				unsigned rl = input & 0x030;
+				unsigned ud = input & 0x0C0;
+				input &= 0x30F;
+				if (rl != 0x030) {
+					input |= rl;
+				}
+				if (ud != 0x0C0) {
+					input |= ud;
+				}
+			}
 			if (gba->rr && gba->rr->isRecording(gba->rr)) {
 				gba->rr->logInput(gba->rr, input);
 			}