From 91ff26fdeab2e5c0426c92794cd5277fa53825c9 Mon Sep 17 00:00:00 2001
From: n loewen <nick@nloewen.com>
Date: Wed, 2 Aug 2023 10:38:58 +0100
Subject: [PATCH] Move display memory and add a pointer to display memory

---
 assembler.js | 6 +++++-
 display.js   | 5 ++++-
 simulator.js | 2 +-
 3 files changed, 10 insertions(+), 3 deletions(-)

diff --git a/assembler.js b/assembler.js
index 29e227c..7f6f86e 100644
--- a/assembler.js
+++ b/assembler.js
@@ -5,7 +5,8 @@ const printMemory = require('./print-memory.js');
 // 3 = always print
 // 4 = silent
 const DEBUG = 4;
-const INITIAL_IP_ADDRESS = 32;
+const INITIAL_IP_ADDRESS = 48;
+const START_OF_DISPLAY_MEM = 0;
 
 const mnemonicsWithOptionalArgs = ['end', 'cfc', 'chp'];
 const mnemonics2opcodes = {
@@ -22,7 +23,10 @@ const mnemonics2opcodes = {
 
 function decodeInstructions(str) {
   let lines = str.split(/\n/); // returns an array of lines
+
   let machineCode = new Array(INITIAL_IP_ADDRESS).fill(0);
+  machineCode[0] = START_OF_DISPLAY_MEM;
+
   let labels = {};
   let IP = INITIAL_IP_ADDRESS;
   for (let i = 0; i < lines.length; i++) {
diff --git a/display.js b/display.js
index 0da75e7..0373ac3 100644
--- a/display.js
+++ b/display.js
@@ -1,5 +1,8 @@
+const START_OF_DISPLAY_MEM = 0;
+
 exports.printDisplay = (mem) => {
-  for (let i = 0; i < 16; i += 4) {
+  const disp = START_OF_DISPLAY_MEM;
+  for (let i = disp; i < disp + 16; i += 4) {
     console.log(`${pad(mem[i])} ${pad(mem[i+1])} ${pad(mem[i+2])} ${pad(mem[i+3])}`);
   }
 }
diff --git a/simulator.js b/simulator.js
index 4401a2c..868a12c 100644
--- a/simulator.js
+++ b/simulator.js
@@ -3,7 +3,7 @@
 // - instructions are two bytes long:
 //   one byte for the opcode, one for the argument
 
-const INITIAL_IP_ADDRESS = 32;
+const INITIAL_IP_ADDRESS = 48;
 const CYCLE_LIMIT = 128; // max number of times to step the CPU, to stop endless loops
 
 const display = require('./display.js');