fix R0 bug

README.md

@@ -69,4 +69,4 @@ HLT
 
 ## Known bugs
 
-- R0 is not usable (confusion with NOP opcode 0 in memory)
+- None for now? If you find one, please open an issue.

cpu.c

@@ -197,7 +197,7 @@ void cpu_dump()
 {
 	printf("\n*** CPU state dump ***\nPC: 0x%x\nEqual flag: %d\nHalted: %d\n\n", cpu.pc, cpu.equal_flag, cpu.halted);
 
-	for (size_t i=1; i<NUM_REGISTERS; i+=2)
+	for (size_t i=0; i<NUM_REGISTERS; i+=2)
 	{
 		printf("R%lu: 0x%04x  R%lu: 0x%04x\n", i, cpu.reg[i], i+1, cpu.reg[i+1]);
 	}

cpu.h

@@ -13,12 +13,9 @@
 
 typedef enum
 {
-	// 0x00 -> No operation
-	NOP 	= 0,
-
 	// 0xA? -> Memory operations
 	MOV 	= 0xA0,
-	PUT		= 0xA1,
+	PUT	= 0xA1,
 
 	// 0xB? -> Arithmetic operations
 	ADD 	= 0xB0,
@@ -41,12 +38,13 @@ typedef enum
 	CMP 	= 0xE2,
 	
 	// 0xF? -> Misc operations
+	NOP	= 0xFE,
 	HLT 	= 0xFF
 } instruction_set_t;
 
 /*
  * CPU structure definition
- * Contains 4 8-bit registers, memory, a program counter, a halt switch, and flags.
+ * Contains 8-bit registers, memory, a program counter, a halt switch, and flags.
 */
 
 typedef struct

program.asm

@@ -1,6 +1,6 @@
 ;this is a comment
-PUT R2, 5
+PUT R0, 5
 PUT R3, 2
-DIV R2, R3
+ADD R0, R3
 
 HLT