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222 lines
5.0 KiB
C++
222 lines
5.0 KiB
C++
//
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// CommandDecoder.hpp
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// Clock Signal
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//
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// Created by Thomas Harte on 24/11/2023.
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// Copyright © 2023 Thomas Harte. All rights reserved.
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//
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#ifndef CommandDecoder_hpp
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#define CommandDecoder_hpp
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#include <cstdint>
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#include <cstddef>
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#include <vector>
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namespace Intel::i8272 {
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enum class Command {
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ReadData = 0x06,
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ReadDeletedData = 0x0c,
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WriteData = 0x05,
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WriteDeletedData = 0x09,
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ReadTrack = 0x02,
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ReadID = 0x0a,
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FormatTrack = 0x0d,
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ScanLow = 0x11,
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ScanLowOrEqual = 0x19,
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ScanHighOrEqual = 0x1d,
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Recalibrate = 0x07,
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Seek = 0x0f,
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SenseInterruptStatus = 0x08,
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Specify = 0x03,
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SenseDriveStatus = 0x04,
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Invalid = 0x00,
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};
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class CommandDecoder {
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public:
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/// Add a byte to the current command.
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void push_back(uint8_t byte) {
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command_.push_back(byte);
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}
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/// Reset decoding.
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void clear() {
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command_.clear();
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}
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/// @returns @c true if an entire command has been received; @c false if further bytes are needed.
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bool has_command() const {
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if(!command_.size()) {
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return false;
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}
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static constexpr std::size_t required_lengths[32] = {
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0, 0, 9, 3, 2, 9, 9, 2,
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1, 9, 2, 0, 9, 6, 0, 3,
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0, 9, 0, 0, 0, 0, 0, 0,
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0, 9, 0, 0, 0, 9, 0, 0,
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};
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return command_.size() >= required_lengths[command_[0] & 0x1f];
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}
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/// @returns The command requested. Valid only if @c has_command() is @c true.
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Command command() const {
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const auto command = Command(command_[0] & 0x1f);
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switch(command) {
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case Command::ReadData: case Command::ReadDeletedData:
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case Command::WriteData: case Command::WriteDeletedData:
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case Command::ReadTrack: case Command::ReadID:
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case Command::FormatTrack:
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case Command::ScanLow: case Command::ScanLowOrEqual:
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case Command::ScanHighOrEqual:
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case Command::Recalibrate: case Command::Seek:
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case Command::SenseInterruptStatus:
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case Command::Specify: case Command::SenseDriveStatus:
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return command;
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default: return Command::Invalid;
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}
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}
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//
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// Commands that specify geometry; i.e.
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//
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// * ReadData;
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// * ReadDeletedData;
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// * WriteData;
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// * WriteDeletedData;
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// * ReadTrack;
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// * ScanEqual;
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// * ScanLowOrEqual;
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// * ScanHighOrEqual.
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//
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/// @returns @c true if this command specifies geometry, in which case geomtry() is well-defined.
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/// @c false otherwise.
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bool has_geometry() const { return command_.size() == 9; }
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struct Geometry {
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uint8_t cylinder, head, sector, size, end_of_track;
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};
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Geometry geometry() const {
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Geometry result;
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result.cylinder = command_[2];
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result.head = command_[3];
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result.sector = command_[4];
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result.size = command_[5];
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result.end_of_track = command_[6];
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return result;
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}
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//
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// Commands that imply data access; i.e.
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//
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// * ReadData;
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// * ReadDeletedData;
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// * WriteData;
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// * WriteDeletedData;
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// * ReadTrack;
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// * ReadID;
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// * FormatTrack;
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// * ScanLow;
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// * ScanLowOrEqual;
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// * ScanHighOrEqual.
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//
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/// @returns @c true if this command involves reading or writing data, in which case target() will be valid.
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/// @c false otherwise.
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bool is_access() const {
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switch(command()) {
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case Command::ReadData: case Command::ReadDeletedData:
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case Command::WriteData: case Command::WriteDeletedData:
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case Command::ReadTrack: case Command::ReadID:
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case Command::FormatTrack:
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case Command::ScanLow: case Command::ScanLowOrEqual:
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case Command::ScanHighOrEqual:
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return true;
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default:
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return false;
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}
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}
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struct AccessTarget {
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uint8_t drive, head;
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bool mfm, skip_deleted;
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};
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AccessTarget target() const {
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AccessTarget result;
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result.drive = command_[1] & 0x03;
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result.head = (command_[1] >> 2) & 0x01;
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result.mfm = command_[0] & 0x40;
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result.skip_deleted = command_[0] & 0x20;
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return result;
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}
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uint8_t drive_head() const {
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return command_[1] & 7;
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}
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//
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// Command::FormatTrack
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//
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struct FormatSpecs {
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uint8_t bytes_per_sector;
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uint8_t sectors_per_track;
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uint8_t gap3_length;
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uint8_t filler;
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};
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FormatSpecs format_specs() const {
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FormatSpecs result;
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result.bytes_per_sector = command_[2];
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result.sectors_per_track = command_[3];
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result.gap3_length = command_[4];
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result.filler = command_[5];
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return result;
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}
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//
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// Command::Seek
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//
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/// @returns The desired target track.
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uint8_t seek_target() const {
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return command_[2];
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}
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//
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// Command::Specify
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//
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struct SpecifySpecs {
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// The below are all in milliseconds.
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uint8_t step_rate_time;
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uint8_t head_unload_time;
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uint8_t head_load_time;
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bool use_dma;
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};
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SpecifySpecs specify_specs() const {
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SpecifySpecs result;
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result.step_rate_time = 16 - (command_[1] >> 4); // i.e. 1 to 16ms
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result.head_unload_time = uint8_t((command_[1] & 0x0f) << 4); // i.e. 16 to 240ms
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result.head_load_time = command_[2] & ~1; // i.e. 2 to 254 ms in increments of 2ms
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result.use_dma = !(command_[2] & 1);
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return result;
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}
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private:
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std::vector<uint8_t> command_;
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};
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}
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#endif /* CommandDecoder_hpp */
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