68k: MOVEM - pre-decrement long-writes on an address register store lsw first and then msw

Author: Federico Berti

src/m68k/cpu/instructions/MOVEM.java

@@ -666,9 +666,9 @@ protected final int putMultipleLongPreDec(int reg, int reglist, int address)
 			{
 				start -= 4;
 				if (reg == 7-n)                         	// if the EA register itself is also moved, use initial value
-					cpu.writeMemoryLong(start, oldreg);
+                    writeMemoryLongSwapped(start, oldreg);
 				else
-					cpu.writeMemoryLong(start, cpu.getAddrRegisterLong(7 - n));
+                    writeMemoryLongSwapped(start, cpu.getAddrRegisterLong(7 - n));
 				regcount++;
 			}
 			bit <<= 1;
@@ -679,7 +679,7 @@ protected final int putMultipleLongPreDec(int reg, int reglist, int address)
 			if((reglist & bit) != 0)
 			{
 				start -= 4;
-				cpu.writeMemoryLong(start, cpu.getDataRegisterLong(7 - n));
+                writeMemoryLongSwapped(start, cpu.getDataRegisterLong(7 - n));
 				regcount++;
 			}
 			bit <<= 1;
@@ -689,4 +689,9 @@ protected final int putMultipleLongPreDec(int reg, int reglist, int address)
 		return regcount;
 	}
 
+    private void writeMemoryLongSwapped(int address, int value) {
+        //swap word-write order, lsw first
+        cpu.writeMemoryWord(address + 2, value & 0xFFFF);
+        cpu.writeMemoryWord(address, (value >> 16) & 0xFFFF);
+    }
 }

test/m68k/cpu/instructions/AddressRegisterPreDecOperandTest.java

@@ -33,6 +33,13 @@ public void writeWord(int addr, int value) {
                 wordWrites.put(addr, value);
                 super.writeWord(addr, value);
             }
+
+            @Override
+            public void writeLong(int addr, int value) {
+                wordWrites.put(addr, (value >> 16) & 0xFFFF);
+                wordWrites.put(addr + 2, value & 0xFFFF);
+                super.writeLong(addr, value);
+            }
         };
 
         cpu = new MC68000();
@@ -42,7 +49,7 @@ public void writeWord(int addr, int value) {
         wordWrites.clear();
     }
 
-    public void testLswWrittenFirst() {
+    public void testLswWrittenFirst_MOVE() {
         int lsw = 0x2222;
         int msw = 0x1111;
         int value = msw << 16 | lsw;
@@ -73,6 +80,40 @@ public void testLswWrittenFirst() {
         Map.Entry<Integer, Integer> second = i.next();
         Assert.assertEquals(firstWordPos, second.getKey().intValue());
         Assert.assertEquals(msw, second.getValue().intValue());
+    }
+
+    public void testLswWrittenFirst_MOVEM() {
+        int lsw = 0x2222;
+        int msw = 0x1111;
+        int value = msw << 16 | lsw;
+        int startPos = 0x104;
+        int endPos = startPos - 8; // 2 longs
+        int valuePos = startPos - 4;
+
+        bus.writeLong(4, 0x48e1_8100);    //48e1 8100                movem.l  d0/d7,-(a1)
+        cpu.setPC(4);
+        cpu.setDataRegisterLong(7, value);
+        cpu.setAddrRegisterLong(1, startPos);
 
+        wordWrites.clear();
+        cpu.execute();
+
+        Assert.assertEquals(cpu.getAddrRegisterLong(1), endPos);
+
+        long res = bus.readLong(valuePos);
+        Assert.assertEquals(res, value);
+
+        Assert.assertEquals(wordWrites.size(), 4);
+
+        int firstWordPos = startPos - 2;
+        Iterator<Map.Entry<Integer, Integer>> i = wordWrites.entrySet().iterator();
+        Map.Entry<Integer, Integer> first = i.next();
+        Assert.assertEquals(firstWordPos, first.getKey().intValue());
+        Assert.assertEquals(lsw, first.getValue().intValue());
+
+        int secondWordPos = firstWordPos - 2;
+        Map.Entry<Integer, Integer> second = i.next();
+        Assert.assertEquals(secondWordPos, second.getKey().intValue());
+        Assert.assertEquals(msw, second.getValue().intValue());
     }
 }