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105 lines
2.5 KiB
C++
105 lines
2.5 KiB
C++
//
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// CAS.cpp
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// Clock Signal
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//
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// Created by Thomas Harte on 25/11/2017.
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// Copyright © 2017 Thomas Harte. All rights reserved.
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//
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#include "CAS.hpp"
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#include <cstring>
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using namespace Storage::Tape;
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namespace {
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const uint8_t header_signature[8] = {0x1f, 0xa6, 0xde, 0xba, 0xcc, 0x13, 0x7d, 0x74};
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}
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CAS::CAS(const char *file_name) :
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file_(file_name) {
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file_.read(input_, sizeof(input_));
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if(std::memcmp(input_, header_signature, sizeof(header_signature))) throw ErrorNotCAS;
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}
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bool CAS::is_at_end() {
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return file_.eof();
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}
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void CAS::virtual_reset() {
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file_.seek(0, SEEK_SET);
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file_.read(input_, sizeof(input_));
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phase_ = Phase::Header;
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distance_into_phase_ = 0;
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}
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Tape::Pulse CAS::virtual_get_next_pulse() {
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Pulse pulse;
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switch(phase_) {
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case Phase::Gap: {
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// Leave a fixed 0.5 second gap between blocks.
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pulse.length.length = 2400;
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pulse.length.clock_rate = 4800;
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pulse.type = Pulse::Type::Zero;
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if(!file_.eof()) phase_ = Phase::Header;
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} break;
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case Phase::Header: {
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// 1 bits are two complete cycle at 2400 hz
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pulse.length.length = 1;
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pulse.length.clock_rate = 4800;
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pulse.type = (distance_into_phase_&1) ? Pulse::Type::Low : Pulse::Type::High;
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distance_into_phase_++;
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if(distance_into_phase_ == 7936*4) {
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distance_into_phase_ = 0;
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phase_ = Phase::Bytes;
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for(int c = 1; c < 8; c++) {
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input_[c] = file_.get8();
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}
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}
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} break;
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case Phase::Bytes: {
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unsigned int bit;
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const int bit_offset = distance_into_phase_ >> 2;
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switch(bit_offset) {
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case 0: bit = 0; break;
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default: bit = (input_[0] >> (bit_offset - 1)) & 1; break;
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case 9:
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case 10: bit = 1; break;
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}
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// 1 bits are two complete cycle at 2400 hz; 0 bits are one complete cycle at 1200 hz
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pulse.length.length = 2 - bit;
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pulse.length.clock_rate = 4800;
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pulse.type = distance_into_phase_ ? Pulse::Type::High : Pulse::Type::Low;
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int adder = 1;
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if(!bit && ((distance_into_phase_&3) == 1)) adder = 3;
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distance_into_phase_ = (distance_into_phase_ + adder) % (11 * 4);
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} break;
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}
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// if(pulse.type == Pulse::Type::Zero) printf("\n---\n");
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// else {
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// if(pulse.length.length == 1) printf(".");
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// else if(pulse.length.length == 2) printf("+");
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// else printf("?");
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// }
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if(!distance_into_phase_ && phase_ == Phase::Bytes) {
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std::memmove(input_, &input_[1], 7);
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input_[7] = file_.get8();
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if(!is_at_end()) {
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if(!std::memcmp(input_, header_signature, sizeof(header_signature))) {
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phase_ = Phase::Header;//Gap;
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}
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}
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}
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return pulse;
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}
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