comments

main.c

 				reg = (opcode & 0x0F00) >> 8;
 				switch ((byte) opcode)
 				{
-					case 0x07:
+					case 0x07: // set reg to delay time
 						if (DEBUG) printf("Copying delay timer to reg %i (%hx)", reg, state.registers[reg]);
 						state.registers[reg] = delay;
 						break;
 
-					case 0x0A:
+					case 0x0A: // wait for input and store it in reg
 						wait = 1;
 						store = reg;
 						break;
 
-					case 0x15:
+					case 0x15: // set delay timer to value in reg
 						delay = state.registers[reg];
 						break;
 
-					case 0x18:
+					case 0x18: // set sound timer to value in reg
 						sound = state.registers[reg];
 						break;
 
-					case 0x1E:
+					case 0x1E: // Add value stored in VX to I
 						state.address_I += state.registers[reg];
 						if (DEBUG) printf("Adding reg %i (%hx) to I (%x)", reg, state.registers[reg], state.address_I);
 						break;
 
-					case 0x29:
+					case 0x29: // set I to address of font character
 						state.address_I = state.registers[reg] * 5;
 						break;
 
-					case 0x33:;
+					case 0x33:; // encode value in reg as a BCD at I, I+1, I+2
 						int value = state.registers[reg];
 						state.memory[state.address_I] = value / 100;
 						state.memory[state.address_I + 1] = (value / 10) % 10;
 						state.memory[state.address_I + 2] = value % 10;
 						break;
 
-					case 0x55:
+					case 0x55: // dump registers V0 -> VX at I
 						for (int i = 0; i <= reg; ++i)
 							state.memory[state.address_I + i] = state.registers[i];
 						break;
 
-					case 0x65:
+					case 0x65: // retrieve registers V0 -> VX from I
 						for (int i = 0; i <= reg; ++i)
 							state.registers[i] = state.memory[state.address_I + i];
 						break;