CLK/Machines/Amiga/DMADevice.hpp

//
//  DMADevice.hpp
//  Clock Signal
//
//  Created by Thomas Harte on 14/09/2021.
//  Copyright © 2021 Thomas Harte. All rights reserved.
//

#pragma once

#include <array>
#include <cstddef>
#include <cstdint>

#include "Flags.hpp"

namespace Amiga {

class Chipset;

class DMADeviceBase {
	public:
		DMADeviceBase(Chipset &chipset, uint16_t *ram, size_t word_size) :
			chipset_(chipset), ram_(ram), ram_mask_(uint32_t(word_size - 1)) {}

		void posit_interrupt(Amiga::InterruptFlag::FlagT);

	protected:
		Chipset &chipset_;
		uint16_t *const ram_ = nullptr;
		const uint32_t ram_mask_ = 0;
};

template <size_t num_addresses, size_t num_modulos = 0> class DMADevice: public DMADeviceBase {
	public:
		using DMADeviceBase::DMADeviceBase;

		/// Writes the word @c value to the address register @c id, shifting it by @c shift (0 or 16) first.
		template <int id, int shift> void set_pointer(uint16_t value) {
			static_assert(id < num_addresses);
			static_assert(shift == 0 || shift == 16);

			byte_pointer_[id] = (byte_pointer_[id] & (0xffff'0000 >> shift)) | uint32_t(value << shift);
			pointer_[id] = byte_pointer_[id] >> 1;
		}

		/// Writes the word @c value to the modulo register @c id, shifting it by @c shift (0 or 16) first.
		template <int id> void set_modulo(uint16_t value) {
			static_assert(id < num_modulos);

			// Convert by sign extension.
			modulos_[id] = uint32_t(int16_t(value) >> 1);
		}

		template <int id, int shift> uint16_t get_pointer() {
			// Restore the original least-significant bit.
			const uint32_t source = (pointer_[id] << 1) | (byte_pointer_[id] & 1);
			return uint16_t(source >> shift);
		}

	protected:
		// These are shifted right one to provide word-indexing pointers;
		// subclasses should use e.g. ram_[pointer_[0] & ram_mask_] directly.
		std::array<uint32_t, num_addresses> pointer_{};
		std::array<uint32_t, num_modulos> modulos_{};

	private:
		std::array<uint32_t, num_addresses> byte_pointer_{};
};

}