CLK/Components/8272/CommandDecoder.hpp

//
//  CommandDecoder.hpp
//  Clock Signal
//
//  Created by Thomas Harte on 24/11/2023.
//  Copyright © 2023 Thomas Harte. All rights reserved.
//

#ifndef CommandDecoder_hpp
#define CommandDecoder_hpp

#include <cstdint>
#include <cstddef>
#include <vector>

namespace Intel::i8272 {

enum class Command {
	ReadData = 0x06,
	ReadDeletedData = 0x0c,

	WriteData = 0x05,
	WriteDeletedData = 0x09,

	ReadTrack = 0x02,
	ReadID = 0x0a,
	FormatTrack = 0x0d,

	ScanLow = 0x11,
	ScanLowOrEqual = 0x19,
	ScanHighOrEqual = 0x1d,

	Recalibrate = 0x07,
	Seek = 0x0f,

	SenseInterruptStatus = 0x08,
	Specify = 0x03,
	SenseDriveStatus = 0x04,

	Invalid = 0x00,
};

class CommandDecoder {
	public:
		/// Add a byte to the current command.
		void push_back(uint8_t byte) {
			command_.push_back(byte);
		}

		/// Reset decoding.
		void clear() {
			command_.clear();
		}

		/// @returns @c true if an entire command has been received; @c false if further bytes are needed.
		bool has_command() const {
			if(!command_.size()) {
				return false;
			}

			static constexpr std::size_t required_lengths[32] = {
				0,	0,	9,	3,	2,	9,	9,	2,
				1,	9,	2,	0,	9,	6,	0,	3,
				0,	9,	0,	0,	0,	0,	0,	0,
				0,	9,	0,	0,	0,	9,	0,	0,
			};

			return command_.size() >= required_lengths[command_[0] & 0x1f];
		}

		/// @returns The command requested. Valid only if @c has_command() is @c true.
		Command command() const {
			const auto command = Command(command_[0] & 0x1f);

			switch(command) {
				case Command::ReadData:		case Command::ReadDeletedData:
				case Command::WriteData:	case Command::WriteDeletedData:
				case Command::ReadTrack:	case Command::ReadID:
				case Command::FormatTrack:
				case Command::ScanLow:		case Command::ScanLowOrEqual:
				case Command::ScanHighOrEqual:
				case Command::Recalibrate:	case Command::Seek:
				case Command::SenseInterruptStatus:
				case Command::Specify:		case Command::SenseDriveStatus:
					return command;

				default: return Command::Invalid;
			}
		}

		//
		// Commands that specify geometry; i.e.
		//
		//	* ReadData;
		//	* ReadDeletedData;
		//	* WriteData;
		//	* WriteDeletedData;
		//	* ReadTrack;
		//	* ScanEqual;
		//	* ScanLowOrEqual;
		//	* ScanHighOrEqual.
		//

		/// @returns @c true if this command specifies geometry, in which case geomtry() is well-defined.
		/// @c false otherwise.
		bool has_geometry() const	{	return command_.size() == 9;	}
		struct Geometry {
			uint8_t cylinder, head, sector, size, end_of_track;
		};
		Geometry geometry() const {
			Geometry result;
			result.cylinder = command_[2];
			result.head = command_[3];
			result.sector = command_[4];
			result.size = command_[5];
			result.end_of_track = command_[6];
			return result;
		}

		//
		// Commands that imply data access; i.e.
		//
		//	* ReadData;
		//	* ReadDeletedData;
		//	* WriteData;
		//	* WriteDeletedData;
		//	* ReadTrack;
		//	* ReadID;
		//	* FormatTrack;
		//	* ScanLow;
		//	* ScanLowOrEqual;
		//	* ScanHighOrEqual.
		//

		/// @returns @c true if this command involves reading or writing data, in which case target() will be valid.
		/// @c false otherwise.
		bool is_access() const {
			switch(command()) {
				case Command::ReadData:		case Command::ReadDeletedData:
				case Command::WriteData:	case Command::WriteDeletedData:
				case Command::ReadTrack:	case Command::ReadID:
				case Command::FormatTrack:
				case Command::ScanLow:		case Command::ScanLowOrEqual:
				case Command::ScanHighOrEqual:
					return true;

				default:
					return false;
			}
		}
		struct AccessTarget {
			uint8_t drive, head;
			bool mfm, skip_deleted;
		};
		AccessTarget target() const {
			AccessTarget result;
			result.drive = command_[1] & 0x03;
			result.head = (command_[1] >> 2) & 0x01;
			result.mfm = command_[0] & 0x40;
			result.skip_deleted = command_[0] & 0x20;
			return result;
		}
		uint8_t drive_head() const {
			return command_[1] & 7;
		}

		//
		// Command::FormatTrack
		//

		struct FormatSpecs {
			uint8_t bytes_per_sector;
			uint8_t sectors_per_track;
			uint8_t gap3_length;
			uint8_t filler;
		};
		FormatSpecs format_specs() const {
			FormatSpecs result;
			result.bytes_per_sector = command_[2];
			result.sectors_per_track = command_[3];
			result.gap3_length = command_[4];
			result.filler = command_[5];
			return result;
		}

		//
		// Command::Seek
		//

		/// @returns The desired target track.
		uint8_t seek_target() const {
			return command_[2];
		}

		//
		// Command::Specify
		//

		struct SpecifySpecs {
			// The below are all in milliseconds.
			uint8_t step_rate_time;
			uint8_t head_unload_time;
			uint8_t head_load_time;
			bool use_dma;
		};
		SpecifySpecs specify_specs() const {
			SpecifySpecs result;
			result.step_rate_time = 16 - (command_[1] >> 4);				// i.e. 1 to 16ms
			result.head_unload_time = uint8_t((command_[1] & 0x0f) << 4);	// i.e. 16 to 240ms
			result.head_load_time = command_[2] & ~1;						// i.e. 2 to 254 ms in increments of 2ms
			result.use_dma = !(command_[2] & 1);
			return result;
		}

	private:
		std::vector<uint8_t> command_;
};

}

#endif /* CommandDecoder_hpp */