[Ben Eater] Build a 6502 computer

makerom.c

#include <stdio.h>
#include <unistd.h>

#define SIZE 0x8000

int main() {
    FILE *fp = fopen("rom.bin", "w");

    if (fp != NULL) {
        unsigned char rom[SIZE];
        unsigned char code[] = {
            0xa9, 0xff,       // lda #$f
            0x8d, 0x02, 0x60, // sta $6002

            0xa9, 0x55,       // lda #$55
            0x8d, 0x00, 0x60, // sta $6000

            0xa9, 0xaa,       // lda #$aa
            0x8d, 0x00, 0x60, // sta $6000

            0x4c, 0x05, 0x80, // jmp $8005
        };

        for (int i = 0; i < sizeof(code); i++) {
            rom[i] = code[i];
        }

        for (int i = sizeof(code); i < SIZE; i++) {
            rom[i] = 0xea;
        }

        rom[0x7ffc] = 0x00;
        rom[0x7ffd] = 0x80;

        fwrite((char *)rom, 1, SIZE, fp);

        fclose(fp);

        return 0;
    }

    return 1;
}

makerom.cpp

#include <stdio.h>
#include <fstream>

#define SIZE 0x8000

//
// Please see this video for details:
// https://www.youtube.com/watch?v=yl8vPW5hydQ
//

int main() {
    std::ofstream file;

    file.open("rom.bin", std::ios::binary | std::ios::out);

    if (file.is_open()) {
        unsigned char rom[SIZE];
        unsigned char code[] = {
            0xa9, 0xff,         // lda #$f
            0x8d, 0x02, 0x60,   // sta $6002

            0xa9, 0x55,         // lda #$55
            0x8d, 0x00, 0x60,   // sta $6000

            0xa9, 0xaa,         // lda #$aa
            0x8d, 0x00, 0x60,   // sta $6000

            0x4c, 0x05, 0x80,   // jmp $8005
        };

        for (int i = 0; i < sizeof(code); i++)
            rom[i] = code[i];

        std::fill(&rom[sizeof(code)], &rom[SIZE], 0xea);

        rom[0x7ffc] = 0x00;
        rom[0x7ffd] = 0x80;

        file.write((char*)rom, sizeof(rom));
        file.close();

        return EXIT_SUCCESS;
    }

    return EXIT_FAILURE;
}

makerom.py

#
# Please see this video for details:
# https://www.youtube.com/watch?v=yl8vPW5hydQ
#
code = bytearray([
  0xa9, 0xff,         # lda #$ff
  0x8d, 0x02, 0x60,   # sta $6002

  0xa9, 0x55,         # lda #$55
  0x8d, 0x00, 0x60,   # sta $6000

  0xa9, 0xaa,         # lda #$aa
  0x8d, 0x00, 0x60,   # sta $6000

  0x4c, 0x05, 0x80,   # jmp $8005
  ])

rom = code + bytearray([0xea] * (32768 - len(code)))

rom[0x7ffc] = 0x00
rom[0x7ffd] = 0x80

with open("rom.bin", "wb") as out_file:
  out_file.write(rom)
  

Please see this video for details.