标签：#emulator

The reason I started this project is to learn more about C++, as we all know the best way of learning a programming language is to do projects, DO PROJECTS!! I used Austin Morlan's website to learn how to build it, it's quite good ( https://austinmorlan.com/posts/chip8_emulator/ ). I made some tweaks which I found to be better for me. I will not be posting the whole codebase here, it's too long. What I will be sharing are snippets of code, what I learned from it, and what I found amazing or funny (projects can have their own jokes). What is an Emulator ? An emulator is just hardware or software that lets the host system replicate conditions like the CPU, memory systems, clock cycles, etc., of the guest system whose functions/behaviour they want to simulate. It helps to bridge the architectural gap by making sure that each instruction code can be executed. In the case of Chip8, we have to simulate the hardware restrictions of the 1970s: a 64x32 screen, a 16-key keypad, timers, and a buzz sound. If you google Chip8, you will see that it is not actually a real physical device. It is a virtual machine/interpreter where you can interpret games (that was the intended purpose), like Pong or Space Invaders. It was a virtual language created in 1977 AD for a computer called COSMAC VIP. Building in C++ I wanted to get familiar with C++, that's why I am here. Building a Chip8 emulator in C++. Well, I learned you need headers, classes to define objects, the standard library, built-in objects like std::ifstream, std::streampos, and so on. I will explain some parts that left a mark in my memory. Header Files Well, before C++, I had only used a header file for an FPGA (Tang Nano 9K) project which I did. It made the LED blink in intervals. But now I understand more, such as how we create a blueprint of the class which we will be using to create objects in the future. Two modes: Public: The attributes and methods of the said class can be accessed by other functions or parts of the p

Over the course of a few posts, I will be constructing an NES emulator that will allow you to play NES ROMs. Today’s post is the first in this series, where I will be walking through the process of emulating the CPU the NES used, the MOS 6502. STRUCTURE The 6502 has 6 primary registers we need to emulate in our program. The A register is the accumulator, which is 1 byte long The X register is an index register, which is also 1 byte long The Y register is another index register, also 1 byte long The Program Counter is 2 bytes long, allowing for accessing 65536 memory locations The Stack Pointer is 1 byte long, allowing a 256 byte stack The P register is a status register that is 1 byte long, containing the CPU status flags Below is the struct I used for the 6502 typedef struct { uint8_t A ; uint8_t X ; uint8_t Y ; uint16_t pc ; uint8_t S ; uint8_t P ; } cpu_6502 ; MEMORY The 6502 can read up to 64kb of memory thanks to the 2 byte long program counter. For my implementation, the memory is just a simple uint8_t array declared like so: uint8_t memory[65536] = {0}; This just implements an array of 65536 bytes that we will load programs into, that the CPU will then step through. However, we need to have a function that is able to decode the commands. OPCODES An opcode (operation code) is a number that represents an instruction for the CPU. The 6502 has 56 distinct (useful) opcodes I will be emulating today. A full list of the opcodes can be found in this handy little table. Since there are so many opcodes, I will not go through them all. The full code can be found in my GitHub repo here: https://github.com/benjaminavachon/6502-emulator Here we can discuss a few of the operations so you can get a feel for what they do. The first one we will discuss is very simple. It is LDA; it simply loads the piece of data after the opcode stored in memory into the A register and increments the program counter to the next memory address. A simple example of this would be: LDA 0x05 This i