works now--learned about extern

README.md

@@ -1,3 +1,17 @@
 # lc3-vm
 
 Virtual machine based on the LC-3 architecture.
+
+Inspired from this tutorial: https://www.jmeiners.com/lc3-vm/
+
+Sample programs are included in the `samples/` directory.
+
+**Build:**
+```
+make
+```
+
+**Run:**
+```
+./target/bin/lc3 samples/{sample program here}
+```

src/main.c

@@ -12,6 +12,9 @@
 #include "ops.h"
 #include "traps.h"
 
+u16 memory[MEMORY_MAX];
+u16 reg[R_COUNT];
+u16 running;
 
 // Helper functions
 u16 sign_extend(u16 x, int bit_count) {
@@ -98,11 +101,13 @@ u16 mem_read(u16 address) {
     if (check_key()) {
       memory[MR_KBSR] = (1 << 15);
       memory[MR_KBDR] = getchar();
-    } else {
+    }
+    else {
       memory[MR_KBSR] = 0;
     }
   }
   return memory[address];
+
 }
 
 int main(int argc, char **argv) {
@@ -136,56 +141,49 @@ int main(int argc, char **argv) {
     op = instr >> 12;
 
     switch (op) {
-      case OP_BR:
-        op_br(instr);
-        break;
       case OP_ADD:
         op_add(instr);
         break;
-      case OP_LD:
-        op_ld(instr);
-        break;
-      case OP_ST:
-        op_st(instr);
-        break;
-      case OP_JSR:
-        op_jsr(instr);
-        break;
       case OP_AND:
         op_and(instr);
         break;
-      case OP_LDR:
-        op_ldr(instr);
-        break;
-      case OP_STR:
-        op_str(instr);
-        break;
-      case OP_RTI:
-        // unused
-        abort();
-        break;
       case OP_NOT:
         op_not(instr);
         break;
-      case OP_LDI:
-        op_ldr(instr);
-        break;
-      case OP_STI:
-        op_sti(instr);
+      case OP_BR:
+        op_br(instr);
         break;
       case OP_JMP:
         op_jmp(instr);
         break;
-      case OP_RES:
-        // unused
-        abort();
+      case OP_JSR:
+        op_jsr(instr);
+        break;
+      case OP_LD:
+        op_ld(instr);
+        break;
+      case OP_LDI:
+        op_ldi(instr);
+        break;
+      case OP_LDR:
+        op_ldr(instr);
         break;
       case OP_LEA:
         op_lea(instr);
         break;
+      case OP_ST:
+        op_st(instr);
+        break;
+      case OP_STI:
+        op_sti(instr);
+        break;
+      case OP_STR:
+        op_str(instr);
+        break;
       case OP_TRAP:
         reg[R_R7] = reg[R_PC];
-        switch (instr & 0xFF) {
+        switch (instr & 0xFF)
+        {
           case TRAP_GETC:
             trap_getc();
             break;
@@ -206,10 +204,12 @@ int main(int argc, char **argv) {
             break;
         }
         break;
+      case OP_RES:
+      case OP_RTI:
       default:
-        // invalid opcode
         abort();
         break;
+
     }
   }
 

src/main.h

@@ -39,9 +39,9 @@ enum {
 };
 
 // Global variables
-static u16 memory[MEMORY_MAX];
-static u16 reg[R_COUNT];
-static u16 running;
+extern u16 memory[MEMORY_MAX];
+extern u16 reg[R_COUNT];
+extern u16 running;
 
 u16 sign_extend(u16 x, int bit_count);
 void update_flags(u16 r);

src/traps.c

@@ -28,7 +28,7 @@ void trap_in(void) {
   char c = getchar();
   putc(c, stdout);
   fflush(stdout);
-  reg[R_R0] = (uint16_t)c;
+  reg[R_R0] = (u16)c;
   update_flags(R_R0);
 
 }