diff --git a/dsim.c b/dsim.c
index ac6fd2e..017ce46 100644
--- a/dsim.c
+++ b/dsim.c
@@ -3,6 +3,11 @@
 #include <stdint.h>
 #include <stdbool.h>
 
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <unistd.h>
+
 uint16_t ram[0x10000];
 uint16_t ra, rb, rc, rx, ry, rz, ri, rj;
 uint16_t rpc, rsp, rex, ria;
@@ -47,8 +52,6 @@ void reset()
     running = true;
 }
 
-typedef void (*dev_t)(void);
-
 struct dev_entry {
     uint32_t vendor;
     uint32_t product;
@@ -471,8 +474,8 @@ void next()
     ir = ram[rpc++];
 
     opcode = ir & 0x001f;
-    a = (ir >> 5) & 0x001f;
-    b = (ir >> 10) & 0x003f;
+    a = (ir >> 10) & 0x003f;
+    b = (ir >> 5) & 0x001f;
 
     if (opcode == 0) { /* special instruction */
         f = sops[b];
@@ -492,9 +495,49 @@ void next()
     ticks++;
 }
 
-int main()
+int load_image(char *filename)
 {
-    reset();
-    while (running) next();
+    int fd;
+    ssize_t r;
+    ssize_t pos;
+
+    fd = open(filename, O_RDONLY);
+    if (fd < 0)
+        return fd;
+    for (pos=0;;) {
+        r = read(fd, &ram[pos], sizeof(ram));
+        if (r > 0)
+            pos += r;
+        else {
+            close(fd);
+            if (r == 0)
+                return pos;
+            else
+                return r;
+        }
+    }
+}
+
+void dump_ram(uint16_t addr, uint16_t count)
+{
+    uint16_t i, a;
+
+    for (i=0; i<count; i++) {
+        a = (addr + i) % sizeof(ram);
+        if ((i % 8) == 0)
+            printf("\n%04x: ", a);
+        printf("%04x ", ram[a]);
+    }
+    printf("\n");
+}
+
+int main(int argc, char *argv[])
+{
+    if (argc > 1) {
+        load_image(argv[1]);
+        dump_ram(0, 32);
+        reset();
+        while (running) next();
+    }
     return EXIT_SUCCESS;
 }