diff --git a/src/interp.c b/src/interp.c
index 6b58f1a..c79fbe3 100644
--- a/src/interp.c
+++ b/src/interp.c
@@ -54,6 +54,17 @@ void memory_set8(uint64_t addr, unsigned char byte) {
   }
 }
 
+void memory_set64(uint64_t addr, uint64_t x) {
+  memory_set8(addr+0, (x >> 56) & 0xFF);
+  memory_set8(addr+1, (x >> 48) & 0xFF);
+  memory_set8(addr+2, (x >> 40) & 0xFF);
+  memory_set8(addr+3, (x >> 32) & 0xFF);
+  memory_set8(addr+4, (x >> 24) & 0xFF);
+  memory_set8(addr+5, (x >> 16) & 0xFF);
+  memory_set8(addr+6, (x >>  8) & 0xFF);
+  memory_set8(addr+7, (x >>  0) & 0xFF);
+}
+
 unsigned char memory_get8(uint64_t addr) {
   if (isMMIO(addr)) {
     if (addr == UART_RX) {
@@ -70,6 +81,19 @@ unsigned char memory_get8(uint64_t addr) {
   }
 }
 
+uint64_t memory_get64(uint64_t addr) {
+  return
+    ((uint64_t) memory_get8(addr+0) << 56) +
+    ((uint64_t) memory_get8(addr+1) << 48) +
+    ((uint64_t) memory_get8(addr+2) << 40) +
+    ((uint64_t) memory_get8(addr+3) << 32) +
+    ((uint64_t) memory_get8(addr+4) << 24) +
+    ((uint64_t) memory_get8(addr+5) << 16) +
+    ((uint64_t) memory_get8(addr+6) <<  8) +
+    ((uint64_t) memory_get8(addr+7) <<  0);
+}
+
+
 int load_program(const char *fname) {
   FILE *f = fopen(fname, "rb");
   int byte;
@@ -161,12 +185,24 @@ int main(int argc, char **argv) {
         negativeFlag = (val < 0);
         break;
       }
-      case 0x60: { // AddR64
+      case 0x94: { // Mov64
+        unsigned char dst = inputs[0];
+        unsigned char src = inputs[1];
+        registers[dst] = registers[src];
+        break;
+      }
+      case 0x6E: { // AddR64
         unsigned char dst = inputs[0];
         unsigned char src = inputs[1];
         registers[dst] += registers[src];
         break;
       }
+      case 0x6F: { // SubR64
+        unsigned char dst = inputs[0];
+        unsigned char src = inputs[1];
+        registers[dst] -= registers[src];
+        break;
+      }
       case 0x70: { // MulR64
         unsigned char dst = inputs[0];
         unsigned char src = inputs[1];
@@ -198,6 +234,25 @@ int main(int argc, char **argv) {
         }
         break;
       }
+      case 0x46: { // Call
+        unsigned char addr = inputs[0];
+        xSp -= 8;
+        memory_set64(xSp, xBp);
+        xSp -= 8;
+        memory_set64(xSp, xPc);
+        xBp = xSp;
+        xPc = registers[addr];
+        break;
+      }
+      case 0x02: { // Ret
+        uint64_t addr = memory_get64(xBp);
+        uint64_t oldBase = memory_get64(xBp+8);
+
+        xPc = addr;
+        xSp = xBp+16;
+        xBp = oldBase;
+        break;
+      }
       default: {
         printf("Unknown instruction: 0x%02X\n", inst);
         exit(1);
diff --git a/tests/call.asm b/tests/call.asm
new file mode 100644
index 0000000..e0eb369
--- /dev/null
+++ b/tests/call.asm
@@ -0,0 +1,15 @@
+include "fvm.inc"
+
+org 0x4000000000000000
+start:
+  MovI64 r95, UART_TX
+  call function
+  MovI64 r2, 0x69
+  St8 r2, r95
+  MovI64 r2, 0x0a
+  St8 r2, r95
+  Halt
+function:
+  MovI64 r2, 0x48
+  St8 r2, r95
+  Ret
diff --git a/tests/fvm.inc b/tests/fvm.inc
index 9ac7d46..342e980 100644
--- a/tests/fvm.inc
+++ b/tests/fvm.inc
@@ -13,7 +13,8 @@ define r9 9
 define r10 10
 define r11 11
 define r12 12
-define r13 13 define r14 14
+define r13 13 
+define r14 14
 define r15 15
 define r16 16
 define r17 17
@@ -217,6 +218,12 @@ macro MovI64 dst, val
   _dq_be val
 end macro
 
+macro Mov64 dst, src
+  db 0x94
+  db dst
+  db src
+end macro
+
 macro Ld8 dst, addr
   db 0x93
   db dst
@@ -230,7 +237,13 @@ macro St8 dst, addr
 end macro
 
 macro AddR64 dst, src
-  db 0x60
+  db 0x6E
+  db dst
+  db src
+end macro
+
+macro SubR64 dst, src
+  db 0x6F
   db dst
   db src
 end macro
@@ -278,6 +291,21 @@ macro JmpIZ addr
   JmpRIZ 127
 end macro
 
+macro callR addr
+  db 0x46
+  db addr
+end macro
+
+macro call val
+  MovI64 127, val
+  db 0x46
+  db 127
+end macro
+
+macro Ret
+  db 2
+end macro
+
 macro Halt
   db 0
 end macro