From 60256eb7906deca8d4af788062d067e0b55b1ca6 Mon Sep 17 00:00:00 2001
From: "Victor B." <contact@itsvic.dev>
Date: Fri, 3 May 2024 11:27:55 +0200
Subject: [PATCH] add a handful of undocumented instructions

---
 src/opcodes.cpp      | 44 ++++++++++++++++++++++++++++++--------------
 src/opcodes/load.cpp |  9 ++++++++-
 2 files changed, 38 insertions(+), 15 deletions(-)

diff --git a/src/opcodes.cpp b/src/opcodes.cpp
index 0045b39..9affd11 100644
--- a/src/opcodes.cpp
+++ b/src/opcodes.cpp
@@ -3,11 +3,13 @@
 #include "v6502/opcodeMap.h"
 
 // load
+OPCODE(lax); // Undocumented.
 OPCODE(lda);
-OPCODE(sta);
 OPCODE(ldx);
-OPCODE(stx);
 OPCODE(ldy);
+OPCODE(sax); // Undocumented.
+OPCODE(sta);
+OPCODE(stx);
 OPCODE(sty);
 
 // trans
@@ -83,6 +85,14 @@ OPCODE(nop_mode);
 
 std::map<uint8_t, Opcode> cpuOpcodes = {
     // load
+    {0xAB, {"*LAX #$%02x", lax, IMMEDIATE}},
+    {0xAF, {"*LAX $%04x", lax, ABSOLUTE}},
+    {0xBF, {"*LAX $%04x,Y", lax, Y_ABSOLUTE}},
+    {0xA7, {"*LAX $%02x", lax, ZERO_PAGE}},
+    {0xB7, {"*LAX $%02x,Y", lax, Y_ZERO_PAGE}},
+    {0xA3, {"*LAX ($%02x,X)", lax, X_ZP_INDIRECT}},
+    {0xB3, {"*LAX ($%02x),Y", lax, ZP_INDIRECT_Y}},
+
     {0xA9, {"LDA #$%02x", lda, IMMEDIATE}},
     {0xAD, {"LDA $%04x", lda, ABSOLUTE}},
     {0xBD, {"LDA $%04x,X", lda, X_ABSOLUTE}},
@@ -92,30 +102,35 @@ std::map<uint8_t, Opcode> cpuOpcodes = {
     {0xA1, {"LDA ($%02x,X)", lda, X_ZP_INDIRECT}},
     {0xB1, {"LDA ($%02x),Y", lda, ZP_INDIRECT_Y}},
 
-    {0x8D, {"STA $%04x", sta, ABSOLUTE}},
-    {0x9D, {"STA $%04x,X", sta, X_ABSOLUTE}},
-    {0x99, {"STA $%04x,Y", sta, Y_ABSOLUTE}},
-    {0x85, {"STA $%02x", sta, ZERO_PAGE}},
-    {0x95, {"STA $%02x,X", sta, X_ZERO_PAGE}},
-    {0x81, {"STA ($%02x,X)", sta, X_ZP_INDIRECT}},
-    {0x91, {"STA ($%02x),Y", sta, ZP_INDIRECT_Y}},
-
     {0xA2, {"LDX #$%02x", ldx, IMMEDIATE}},
     {0xAE, {"LDX $%04x", ldx, ABSOLUTE}},
     {0xBE, {"LDX $%04x,Y", ldx, Y_ABSOLUTE}},
     {0xA6, {"LDX $%02x", ldx, ZERO_PAGE}},
     {0xB6, {"LDX $%02x,Y", ldx, Y_ZERO_PAGE}},
 
-    {0x8E, {"STX $%04x", stx, ABSOLUTE}},
-    {0x86, {"STX $%02x", stx, ZERO_PAGE}},
-    {0x96, {"STX $%02x,Y", stx, Y_ZERO_PAGE}},
-
     {0xA0, {"LDY #$%02x", ldy, IMMEDIATE}},
     {0xAC, {"LDY $%04x", ldy, ABSOLUTE}},
     {0xBC, {"LDY $%04x,X", ldy, X_ABSOLUTE}},
     {0xA4, {"LDY $%02x", ldy, ZERO_PAGE}},
     {0xB4, {"LDY $%02x,X", ldy, X_ZERO_PAGE}},
 
+    {0x8F, {"*SAX $%04x", stx, ABSOLUTE}},
+    {0x87, {"*SAX $%02x", stx, ZERO_PAGE}},
+    {0x97, {"*SAX $%02x,Y", stx, Y_ZERO_PAGE}},
+    {0x83, {"*SAX ($%02x,X)", stx, X_ZP_INDIRECT}},
+
+    {0x8D, {"STA $%04x", sta, ABSOLUTE}},
+    {0x9D, {"STA $%04x,X", sta, X_ABSOLUTE}},
+    {0x99, {"STA $%04x,Y", sta, Y_ABSOLUTE}},
+    {0x85, {"STA $%02x", sta, ZERO_PAGE}},
+    {0x95, {"STA $%02x,X", sta, X_ZERO_PAGE}},
+    {0x81, {"STA ($%02x,X)", sta, X_ZP_INDIRECT}},
+    {0x91, {"STA ($%02x),Y", sta, ZP_INDIRECT_Y}},
+
+    {0x8E, {"STX $%04x", stx, ABSOLUTE}},
+    {0x86, {"STX $%02x", stx, ZERO_PAGE}},
+    {0x96, {"STX $%02x,Y", stx, Y_ZERO_PAGE}},
+
     {0x8C, {"STY $%04x", sty, ABSOLUTE}},
     {0x84, {"STY $%02x", sty, ZERO_PAGE}},
     {0x94, {"STY $%02x,X", sty, X_ZERO_PAGE}},
@@ -218,6 +233,7 @@ std::map<uint8_t, Opcode> cpuOpcodes = {
     {0xC4, {"CPY $%02x", cpy, ZERO_PAGE}},
 
     {0xE9, {"SBC #$%02x", sbc, IMMEDIATE}},
+    {0xEB, {"*SBC #$%02x", sbc, IMMEDIATE}},
     {0xED, {"SBC $%04x", sbc, ABSOLUTE}},
     {0xFD, {"SBC $%04x,X", sbc, X_ABSOLUTE}},
     {0xF9, {"SBC $%04x,Y", sbc, Y_ABSOLUTE}},
diff --git a/src/opcodes/load.cpp b/src/opcodes/load.cpp
index 603e68e..a3efff2 100644
--- a/src/opcodes/load.cpp
+++ b/src/opcodes/load.cpp
@@ -1,6 +1,11 @@
 #include "v6502/cpu.h"
 #include "v6502/opcodes.h"
 
+OPCODE(lax) { // Undocumented.
+  cpu->x = cpu->a = cpu->fetchByteWithMode(mode);
+  cpu->evaluateFlags(cpu->a);
+}
+
 OPCODE(lda) {
   cpu->a = cpu->fetchByteWithMode(mode);
   cpu->evaluateFlags(cpu->a);
@@ -15,7 +20,9 @@ OPCODE(ldy) {
   cpu->y = cpu->fetchByteWithMode(mode);
   cpu->evaluateFlags(cpu->y);
 }
-
+OPCODE(sax) { // Undocumented.
+  cpu->bus->write(cpu->fetchEffectiveModeValue(mode), cpu->a & cpu->x);
+}
 OPCODE(sta) { cpu->bus->write(cpu->fetchEffectiveModeValue(mode), cpu->a); }
 OPCODE(stx) { cpu->bus->write(cpu->fetchEffectiveModeValue(mode), cpu->x); }
 OPCODE(sty) { cpu->bus->write(cpu->fetchEffectiveModeValue(mode), cpu->y); }