6502pasm

6502pasm (WIP)

A portable 6502 assembler written in C++

The Goal

I wanted to make a 6502 IDE for the M5Stack Cardputer (an ESP32 based computer), but I couldn’t find an assembler that didn’t rely on the underlying operating system (which the Cardputer doesn’t have) so I’m making my own! I’m hoping to have a 6502 assembler contained in a single file (well, two files including the .h) while using minimal standard libraries (hopefully only stdio for sprintf, stdlib for malloc, and regex)

Todo

• Not-so-critical
  • Auto-allocate variables
  • Math expressions (probably RPN)
  • Errors
  • Expand syntax
    • Decimal and binary numbers
    • Instruction and label on the same line
    • Make label colon optional
  • Maybe use a namespace
  • Update docs

Usage

To test:

• Clone the repo
• Go to test/
• run make main
• run ./main To use in your own project: (DON’T DO IT YET, THIS ISN’T FINISHED)
• Clone the repo
• Copy src/6502pasm.h and src/6502pasm.cpp into your project
• Success!
• If not success, please leave an issue, as I’m trying to make it as easy as possible to integrate

Docs (also WIP)

Assembler() class

This is the class that contains the assembler. It has:

• std::vector<std::string> input_lines: A list of lines, each line has only one thing:
  • a directive (ex. .org $0800)
  • a label (ex. cool_label:)
  • or an instruction (ex. lda #$05)
  • Lines can also have a comment (everything after a ; is ignored)
• std::vector<unsigned char> output_bytes: A list of bytes as the assembled code
• std::vector<Label> labels: A list of labels that were found
• std::vector<Macro> macros: A list of macros that were found
• int assemble(): Assembles the input_lines into the output_bytes. Returns 0 if successful, 1 if not.

Example

#include "6502pasm.h"

int main() {
  Assembler assembler = Assembler();

  // Loads some simple stuff into input_lines
  assembler.input_lines.push_back(std::string(".org $0800"));
  assembler.input_lines.push_back(std::string(".macro addr $05"));
  assembler.input_lines.push_back(std::string("main:"));
  assembler.input_lines.push_back(std::string(" lda #$2e ; comment"));
  assembler.input_lines.push_back(std::string(" LDX $04 ; capital mnemonic"));
  assembler.input_lines.push_back(std::string(" ldy %addr ; macro"));
  assembler.input_lines.push_back(std::string(" jmp main ; uses a label"));

  // Assemble it
  assembler.assemble();

  // Output it
  printf("Output hex (%d bytes):\n",assembler.output_bytes.size());
  for (int i=0;i<assembler.output_bytes.size();i++) {
    if (i%8==0)
      printf("  %02x: ",i);
    printf("%02x ",assembler.output_bytes[i]);
    if (i%8==7)
      printf("\n");
  }
  printf("\n");
  printf("Labels (%d labels):\n",assembler.labels.size());
  for (Label l : assembler.labels) {
    printf("  %s @ 0x%04x\n",l.name.c_str(),l.location);
  }
  printf("Macros (%d macros):\n",assembler.macros.size());
  for (Macro m : assembler.macros) {
    printf("  %s = '%s'\n",m.name.c_str(),m.text.c_str());
  }

  return 0;
}

You can also look at test/main.cpp

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