ch81/cores/board.h

/*
 * Copyright 2026 Michael Hope <michaelh@juju.nz>
 * SPDX-License-Identifier: MIT
 */

#pragma once

#include <cstdint>
#include <span>

namespace ch81 {

// Board implements the board specific memory and IO.
class Board {
 public:
  virtual ~Board() = default;

  // Returns a pointer to the emulated memory at `address`, if any.
  [[nodiscard]] virtual uint8_t* map(uint16_t address) = 0;

  // Reads a byte from memory at `address`.
  [[nodiscard]] virtual uint8_t read(uint16_t address) = 0;

  // Writes `value` to memory at `address`. If `address` is not emulated then
  // the write is discarded.
  virtual void write(uint16_t address, uint8_t value) = 0;

  // Fetches an instruction byte from `address`. A specialised version of
  // `read`.
  [[nodiscard]] virtual uint8_t fetch(uint16_t address) = 0;

  // Reads a byte from I/O port `port`.
  [[nodiscard]] virtual uint8_t in(uint16_t port) = 0;

  // Writes `value` to I/O port `port`. If `port` is not emulated then the write
  // is discarded.
  virtual void out(uint8_t port, uint8_t value) = 0;

  // Returns true if a jump to `target` should also cause an emulator exit.
  [[nodiscard]] virtual bool trap_jump(uint16_t target) = 0;

  // Returns true if an interrupt is pending. May update state.
  [[nodiscard]] virtual bool irqs() = 0;

  [[nodiscard]] virtual uint16_t read16(uint16_t address) {
    return read(address) | (read(address + 1) << 8);
  }

  virtual void write16(uint16_t address, uint16_t value) {
    write(address, value & 0xFF);
    write(address + 1, value >> 8);
  }
};

}  // namespace ch81