diff --git a/src/makefile b/src/makefile
index 427ed8b..17378b4 100755
--- a/src/makefile
+++ b/src/makefile
@@ -192,8 +192,8 @@ $(DRAWL): lisp/s-expr.pla lisp/drawl.pla
 vmsrc/lib6502/lib6502.a: vmsrc/lib6502/lib6502.h vmsrc/lib6502/lib6502.c
 	make -C vmsrc/lib6502
 
-$(PLVM): vmsrc/plvm.c vmsrc/cmdsys.c vmsrc/lib6502/lib6502.a
-	cc vmsrc/plvm.c vmsrc/cmdsys.c vmsrc/lib6502/lib6502.a -o $(PLVM)
+$(PLVM): vmsrc/plvm.c vmsrc/cmdsys.c vmsrc/sysio.c vmsrc/lib6502/lib6502.a
+	cc vmsrc/plvm.c vmsrc/cmdsys.c vmsrc/sysio.c vmsrc/lib6502/lib6502.a -o $(PLVM)
 
 $(PLVMZP_APL): FORCE
 	-mkdir -p rel
@@ -265,7 +265,7 @@ test:	samplesrc/test.pla samplesrc/testlib.pla $(PLVM) $(PLASM)
 	acme --setpc 4094 -o $(TEST) samplesrc/test.a
 	./$(PLASM) -AMOW samplesrc/testlib.pla
 	acme --setpc 4094 -o $(TESTLIB) samplesrc/testlib.a
-	./$(PLVM) test.mod 
+	./$(PLVM) test
 
 $(ED): toolsrc/ed.pla $(PLVM02) $(PLASM) toolsrc/ed.pla
 	./$(PLASM) -AMOW toolsrc/ed.pla
diff --git a/src/vmsrc/cmdsys.c b/src/vmsrc/cmdsys.c
index df43ed0..1e3fd61 100644
--- a/src/vmsrc/cmdsys.c
+++ b/src/vmsrc/cmdsys.c
@@ -491,8 +491,8 @@ int load_mod(M6502 *mpu, byte *mod)
     char filename[128], string[17];
 
     dcitos(mod, filename);
-    printf("Load module %s\n", filename);
-    if (strlen(filename) > 4 && (filename[strlen(filename) - 4] != '.'))
+    if (trace) printf("Load module %s\n", filename);
+    if (strlen(filename) < 4 || (filename[strlen(filename) - 4] != '.'))
         strcat(filename, ".mod");
     fd = open(filename, O_RDONLY, 0);
     if (fd <= 0 && filename[0] != '/' && strlen(filename) < 17)
@@ -770,38 +770,9 @@ int load_mod(M6502 *mpu, byte *mod)
 /*
  * Native CMDSYS routines
  */
-int vm_syscall(M6502 *mpu, uword address, byte data)
-{
-    return address + 1;
-}
-void syscall6502(M6502 *mpu)
-{
-    uword params;
-    byte  cmd, status;
-
-    PULL_ESTK(params);
-    PULL_ESTK(cmd);
-    status = 0;
-    switch (cmd)
-    {
-    }
-    PUSH_ESTK(status);
-}
 void sysexecmod(M6502 *mpu)
 {
 }
-void sysopen(M6502 *mpu)
-{
-}
-void sysclose(M6502 *mpu)
-{
-}
-void sysread(M6502 *mpu)
-{
-}
-void syswrite(M6502 *mpu)
-{
-}
 void syslookuptbl(M6502 *mpu)
 {
     uword sym, addr;
diff --git a/src/vmsrc/plvm.h b/src/vmsrc/plvm.h
index aaab2d4..f8fe926 100644
--- a/src/vmsrc/plvm.h
+++ b/src/vmsrc/plvm.h
@@ -113,3 +113,13 @@ extern int vm_iidef(M6502 *mpu, uword address, byte data);
 extern int vm_exdef(M6502 *mpu, uword address, byte data);
 extern int vm_natvdef(M6502 *mpu, uword address, byte data);
 extern void vm_interp(M6502 *mpu, code *vm_ip);
+/*
+ * System I/O routines
+ */
+extern void sysio_init(void);
+extern void syscall6502(M6502 *mpu);
+extern void sysopen(M6502 *mpu);
+extern void sysclose(M6502 *mpu);
+extern void sysread(M6502 *mpu);
+extern void syswrite(M6502 *mpu);
+
diff --git a/src/vmsrc/sysio.c b/src/vmsrc/sysio.c
new file mode 100644
index 0000000..5835691
--- /dev/null
+++ b/src/vmsrc/sysio.c
@@ -0,0 +1,40 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdarg.h>
+#include <string.h>
+#include <unistd.h>
+#include <fcntl.h>
+#include <ctype.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <termios.h>
+#include "plvm.h"
+
+void syscall6502(M6502 *mpu)
+{
+    uword params;
+    byte  cmd, status;
+
+    PULL_ESTK(params);
+    PULL_ESTK(cmd);
+    status = 0;
+    switch (cmd)
+    {
+    }
+    PUSH_ESTK(status);
+}
+void sysopen(M6502 *mpu)
+{
+}
+void sysclose(M6502 *mpu)
+{
+}
+void sysread(M6502 *mpu)
+{
+}
+void syswrite(M6502 *mpu)
+{
+}
+void sysio_init(void)
+{
+}