From 3aacfdf53750db5bfd58a889ba5ba066a6ebb843 Mon Sep 17 00:00:00 2001
From: Tiger <tiger@stargazer-developments.com>
Date: Sun, 10 Sep 2023 09:42:00 +0200
Subject: [PATCH] Implemented 0x2NNN

---
 include/chip8.h               |  8 ++++++++
 include/instruction_handler.h |  5 +++++
 src/chip8.cpp                 |  8 ++++++++
 src/instruction_handler.cpp   | 12 ++++++++++++
 4 files changed, 33 insertions(+)

diff --git a/include/chip8.h b/include/chip8.h
index 6fc6752..cc5ac2e 100644
--- a/include/chip8.h
+++ b/include/chip8.h
@@ -68,9 +68,17 @@ public:
      */
     [[nodiscard]] unsigned short popFromStack();
 
+    void pushToStack(unsigned short value);
+
     /**
      * Sets the program counter (PC) to the given value
      */
     void setProgramCounter(unsigned short value);
+
+    /**
+     * Gets the program counter (PC)
+     * @return
+     */
+    [[nodiscard]] unsigned short getProgramCounter() const;
 };
 #endif //CHIP8_CHIP8_H
diff --git a/include/instruction_handler.h b/include/instruction_handler.h
index f79aabc..30f4545 100644
--- a/include/instruction_handler.h
+++ b/include/instruction_handler.h
@@ -29,6 +29,11 @@ private:
      * Handles Chip8 instruction 0x1000
      */
     static void handle1000(Chip8&, Instruction);
+
+    /**
+     * Handles Chip8 instruction 0x2000
+     */
+    static void handle2000(Chip8&, Instruction);
 public:
     InstructionHandler();
 
diff --git a/src/chip8.cpp b/src/chip8.cpp
index f35353f..03ff5db 100644
--- a/src/chip8.cpp
+++ b/src/chip8.cpp
@@ -54,6 +54,14 @@ unsigned short Chip8::popFromStack() {
     return value;
 }
 
+void Chip8::pushToStack(unsigned short value) {
+    this->stack.push(value);
+}
+
 void Chip8::setProgramCounter(unsigned short value) {
     this->pc = value;
 }
+
+unsigned short Chip8::getProgramCounter() const {
+    return this->pc;
+}
diff --git a/src/instruction_handler.cpp b/src/instruction_handler.cpp
index edf46a2..ffa736c 100644
--- a/src/instruction_handler.cpp
+++ b/src/instruction_handler.cpp
@@ -56,3 +56,15 @@ void InstructionHandler::handle1000(Chip8& chip8, Instruction instruction) {
     chip8.setProgramCounter(instruction.nnn());
 }
 
+/**
+ * Handles the 0x2NNN Chip8 instruction which is used to call a subroutine at NNN.
+ * This will increments the stack pointer and puts PC on top of the stack.
+ *
+ * @param chip8 The Chip8 instance
+ * @param instruction The Instruction instance
+ */
+void InstructionHandler::handle2000(Chip8& chip8, Instruction instruction) {
+    chip8.pushToStack(chip8.getProgramCounter());
+    chip8.setProgramCounter(instruction.nnn());
+}
+