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129 lines
3.5 KiB
C++
129 lines
3.5 KiB
C++
//
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// Shifter.cpp
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// Clock Signal
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//
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// Created by Thomas Harte on 24/09/2017.
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// Copyright 2017 Thomas Harte. All rights reserved.
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//
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#include "Shifter.hpp"
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#include "Constants.hpp"
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#include "../../../../Numeric/BitSpread.hpp"
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using namespace Storage::Encodings::MFM;
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Shifter::Shifter() : owned_crc_generator_(new CRC::CCITT()), crc_generator_(owned_crc_generator_.get()) {}
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Shifter::Shifter(CRC::CCITT *crc_generator) : crc_generator_(crc_generator) {}
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void Shifter::set_is_double_density(bool is_double_density) {
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is_double_density_ = is_double_density;
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if(!is_double_density) is_awaiting_marker_value_ = false;
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}
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void Shifter::set_should_obey_syncs(bool should_obey_syncs) {
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should_obey_syncs_ = should_obey_syncs;
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}
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void Shifter::add_input_bit(int value) {
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shift_register_ = (shift_register_ << 1) | unsigned(value);
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++bits_since_token_;
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token_ = Token::None;
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if(should_obey_syncs_) {
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if(!is_double_density_) {
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switch(shift_register_ & 0xffff) {
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case Storage::Encodings::MFM::FMIndexAddressMark:
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token_ = Token::Index;
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crc_generator_->reset();
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crc_generator_->add(Storage::Encodings::MFM::IndexAddressByte);
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break;
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case Storage::Encodings::MFM::FMIDAddressMark:
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token_ = Token::ID;
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crc_generator_->reset();
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crc_generator_->add(Storage::Encodings::MFM::IDAddressByte);
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break;
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case Storage::Encodings::MFM::FMDataAddressMark:
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token_ = Token::Data;
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crc_generator_->reset();
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crc_generator_->add(Storage::Encodings::MFM::DataAddressByte);
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break;
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case Storage::Encodings::MFM::FMDeletedDataAddressMark:
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token_ = Token::DeletedData;
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crc_generator_->reset();
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crc_generator_->add(Storage::Encodings::MFM::DeletedDataAddressByte);
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break;
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default:
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break;
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}
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} else {
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switch(shift_register_ & 0xffff) {
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case Storage::Encodings::MFM::MFMIndexSync:
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// This models a bit of slightly weird WD behaviour;
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// if an index sync was detected where it wasn't expected,
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// the WD will resync but also may return the clock bits
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// rather than data bits as the next byte read, depending
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// on framing.
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//
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// TODO: make this optional, if ever a Shifter with
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// well-defined non-WD behaviour is needed.
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//
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// TODO: Verify WD behaviour.
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if(bits_since_token_&1) {
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shift_register_ >>= 1;
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}
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bits_since_token_ = 0;
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is_awaiting_marker_value_ = true;
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token_ = Token::Sync;
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break;
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case Storage::Encodings::MFM::MFMSync:
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bits_since_token_ = 0;
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is_awaiting_marker_value_ = true;
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crc_generator_->set_value(Storage::Encodings::MFM::MFMPostSyncCRCValue);
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token_ = Token::Sync;
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break;
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default:
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break;
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}
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}
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if(token_ != Token::None) {
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bits_since_token_ = 0;
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return;
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}
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}
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if(bits_since_token_ == 16) {
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token_ = Token::Byte;
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bits_since_token_ = 0;
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if(is_awaiting_marker_value_ && is_double_density_) {
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is_awaiting_marker_value_ = false;
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switch(get_byte()) {
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case Storage::Encodings::MFM::IndexAddressByte:
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token_ = Token::Index;
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break;
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case Storage::Encodings::MFM::IDAddressByte:
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token_ = Token::ID;
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break;
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case Storage::Encodings::MFM::DataAddressByte:
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token_ = Token::Data;
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break;
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case Storage::Encodings::MFM::DeletedDataAddressByte:
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token_ = Token::DeletedData;
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break;
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default: break;
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}
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}
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crc_generator_->add(get_byte());
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}
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}
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uint8_t Shifter::get_byte() const {
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return Numeric::unspread_bits(uint16_t(shift_register_));
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}
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