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101 lines
2.2 KiB
C++
101 lines
2.2 KiB
C++
//
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// ZX80O.cpp
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// Clock Signal
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//
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// Created by Thomas Harte on 04/06/2017.
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// Copyright © 2017 Thomas Harte. All rights reserved.
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//
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#include "ZX80O.hpp"
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using namespace Storage::Tape;
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ZX80O::ZX80O(const char *file_name) :
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Storage::FileHolder(file_name) {
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// Files can be no longer than 16 kb
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if(file_stats_.st_size > 16384) throw ErrorNotZX80O;
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// skip the system area
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fseek(file_, 8, SEEK_SET);
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// read the pointer to VARS and the alleged pointer to end of file
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uint16_t vars = fgetc16le();
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end_of_file_ = fgetc16le();
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// VARs should be before end of file
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if(vars > end_of_file_) throw ErrorNotZX80O;
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// end of file should be no further than the actual file size
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if(end_of_file_ - 0x4000 > file_stats_.st_size) throw ErrorNotZX80O;
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// TODO: does it make sense to inspect the tokenised BASIC?
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// It starts at 0x4028 and proceeds as [16-bit line number] [tokens] [0x76],
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// but I'm as yet unable to find documentation of the tokens.
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// then rewind and start again
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virtual_reset();
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}
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void ZX80O::virtual_reset() {
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fseek(file_, 0, SEEK_SET);
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is_past_silence_ = false;
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is_high_ = true;
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bit_pointer_ = 9;
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}
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bool ZX80O::is_at_end() {
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return ftell(file_) == end_of_file_ - 0x4000;
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}
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Tape::Pulse ZX80O::virtual_get_next_pulse() {
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Tape::Pulse pulse;
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// Start with 1 second of silence.
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if(!is_past_silence_ || is_at_end()) {
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pulse.type = Pulse::Type::Zero;
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pulse.length.length = 5;
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pulse.length.clock_rate = 1;
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is_past_silence_ = true;
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return pulse;
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}
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// For each byte, output 8 bits and then silence.
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if(bit_pointer_ == 9) {
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byte_ = (uint8_t)fgetc(file_);
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bit_pointer_ = 0;
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wave_pointer_ = 0;
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}
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// Bytes are stored MSB first.
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if(bit_pointer_ < 8) {
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// waves are of length 150µs
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pulse.length.length = 3;
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pulse.length.clock_rate = 20000;
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if(is_high_) {
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pulse.type = Pulse::Type::High;
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is_high_ = false;
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} else {
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pulse.type = Pulse::Type::Low;
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is_high_ = true;
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int wave_count = (byte_ & (0x80 >> bit_pointer_)) ? 9 : 4;
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wave_pointer_++;
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if(wave_pointer_ == wave_count) {
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bit_pointer_++;
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wave_pointer_ = 0;
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}
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}
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} else {
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// post-waves silence is 1300µs
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pulse.length.length = 13;
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pulse.length.clock_rate = 10000;
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pulse.type = Pulse::Type::Zero;
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bit_pointer_++;
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}
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return pulse;
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}
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