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119 lines
4.3 KiB
C++
119 lines
4.3 KiB
C++
//
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// MFMDiskController.hpp
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// Clock Signal
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//
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// Created by Thomas Harte on 05/08/2017.
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// Copyright © 2017 Thomas Harte. All rights reserved.
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//
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#ifndef MFMDiskController_hpp
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#define MFMDiskController_hpp
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#include "DiskController.hpp"
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#include "../../NumberTheory/CRC.hpp"
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#include "../../ClockReceiver/ClockReceiver.hpp"
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namespace Storage {
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namespace Disk {
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/*!
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Extends Controller with a built-in shift register and FM/MFM decoding logic,
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being able to post event messages to subclasses.
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*/
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class MFMController: public Controller {
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public:
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MFMController(Cycles clock_rate, int clock_rate_multiplier, int revolutions_per_minute);
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protected:
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/// Indicates whether the controller should try to decode double-density MFM content, or single-density FM content.
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void set_is_double_density(bool);
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/// @returns @c true if currently decoding MFM content; @c false otherwise.
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bool get_is_double_density();
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enum DataMode {
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/// When the controller is scanning it will obey all synchronisation marks found, even if in the middle of data.
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Scanning,
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/// When the controller is reading it will ignore synchronisation marks and simply return a new token every sixteen PLL clocks.
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Reading,
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/// When the controller is writing, it will replace the underlying data with that which has been enqueued, posting Event::DataWritten when the queue is empty.
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Writing
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};
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/// Sets the current data mode.
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void set_data_mode(DataMode);
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/*!
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Describes a token found in the incoming PLL bit stream. Tokens can be one of:
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Index: the bit pattern usually encoded at the start of a track to denote the position of the index hole;
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ID: the pattern that begins an ID section, i.e. a sector header, announcing sector number, track number, etc.
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Data: the pattern that begins a data section, i.e. sector contents.
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DeletedData: the pattern that begins a deleted data section, i.e. deleted sector contents.
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Sync: MFM only; the same synchronisation mark is used in MFM to denote the bottom three of the four types
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of token listed above; this class combines notification of that mark and the distinct index sync mark.
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Both are followed by a byte to indicate type. When scanning an MFM stream, subclasses will receive an
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announcement of sync followed by an announcement of one of the above four types of token.
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Byte: reports reading of an ordinary byte, with expected timing bits.
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When the data mode is set to 'reading', only Byte tokens are returned; detection of the other kinds of token
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is suppressed. Controllers will likely want to switch data mode when receiving ID and sector contents, as
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spurious sync signals can otherwise be found in ordinary data, causing framing errors.
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*/
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struct Token {
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enum Type {
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Index, ID, Data, DeletedData, Sync, Byte
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} type;
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uint8_t byte_value;
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};
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/// @returns The most-recently read token from the surface of the disk.
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Token get_latest_token();
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/// @returns The controller's CRC generator. This is automatically fed during reading.
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NumberTheory::CRC16 &get_crc_generator();
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// Events
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enum class Event: int {
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Token = (1 << 0), // Indicates recognition of a new token in the flux stream. Use get_latest_token() for more details.
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IndexHole = (1 << 1), // Indicates the passing of a physical index hole.
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DataWritten = (1 << 2), // Indicates that all queued bits have been written
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};
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/*!
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Subclasses should implement this. It is called every time a new @c Event is discovered in the incoming data stream.
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Therefore it is called to announce when:
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(i) a new token is discovered in the incoming stream: an index, ID, data or deleted data, a sync mark or a new byte of data.
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(ii) the index hole passes; or
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(iii) the queue of data to be written has been exhausted.
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*/
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virtual void posit_event(int type) = 0;
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private:
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// Storage::Disk::Controller
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virtual void process_input_bit(int value, unsigned int cycles_since_index_hole);
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virtual void process_index_hole();
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virtual void process_write_completed();
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// PLL input state
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int bits_since_token_;
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int shift_register_;
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bool is_awaiting_marker_value_;
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// input configuration
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bool is_double_density_;
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DataMode data_mode_;
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// output
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Token latest_token_;
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// CRC generator
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NumberTheory::CRC16 crc_generator_;
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};
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}
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}
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#endif /* MFMDiskController_hpp */
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