Example "in memory" controller pak

controllerpak.c

static uint8_t pak_storage[CONTROLLER_PAK_SIZE];

static void controller_pak_read_block(struct joybus_n64_accessory *accessory, uint16_t addr,
                                      uint8_t buf[JOYBUS_ACCESSORY_BLOCK_SIZE])
{
  // Return zeroes for out-of-bounds addresses
  if (addr >= CONTROLLER_PAK_SIZE) {
    memset(buf, 0, JOYBUS_ACCESSORY_BLOCK_SIZE);
    return;
  }

  // Read the block from RAM into the response buffer
  memcpy(buf, &pak_storage[addr], JOYBUS_ACCESSORY_BLOCK_SIZE);
}

static void controller_pak_write_block(struct joybus_n64_accessory *accessory, uint16_t addr,
                                       const uint8_t buf[JOYBUS_ACCESSORY_BLOCK_SIZE])
{
  // Ignore writes to out-of-bounds addresses
  if (addr >= CONTROLLER_PAK_SIZE)
    return;

  // Write the block to RAM
  memcpy(&pak_storage[addr], buf, JOYBUS_ACCESSORY_BLOCK_SIZE);
}

static const struct joybus_n64_accessory_api controller_pak_api = {
  .read_block  = controller_pak_read_block,
  .write_block = controller_pak_write_block,
};

static struct joybus_n64_accessory controller_pak = {
  .api = &controller_pak_api,
};