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89 lines
2.5 KiB
C++
89 lines
2.5 KiB
C++
//
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// PCMSegment.cpp
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// Clock Signal
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//
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// Created by Thomas Harte on 17/12/2016.
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// Copyright © 2016 Thomas Harte. All rights reserved.
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//
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#include "PCMSegment.hpp"
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using namespace Storage::Disk;
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PCMSegmentEventSource::PCMSegmentEventSource(const PCMSegment &segment) :
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segment_(segment)
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{
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if(segment_.length_of_a_bit.length&1)
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{
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segment_.length_of_a_bit.length <<= 1;
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segment_.length_of_a_bit.clock_rate <<= 1;
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}
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next_event_.length.clock_rate = segment_.length_of_a_bit.clock_rate;
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reset();
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}
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void PCMSegmentEventSource::reset()
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{
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bit_pointer_ = 0;
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next_event_.type = Track::Event::FluxTransition;
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}
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Storage::Disk::Track::Event PCMSegmentEventSource::get_next_event()
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{
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size_t initial_bit_pointer = bit_pointer_;
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next_event_.length.length = bit_pointer_ ? 0 : -(segment_.length_of_a_bit.length >> 1);
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const uint8_t *segment_data = segment_.data.data();
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while(bit_pointer_ < segment_.number_of_bits)
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{
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int bit = segment_data[bit_pointer_ >> 3] & (0x80 >> (bit_pointer_&7));
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bit_pointer_++;
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next_event_.length.length += segment_.length_of_a_bit.length;
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if(bit) return next_event_;
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}
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if(initial_bit_pointer < segment_.number_of_bits) next_event_.length.length += (segment_.length_of_a_bit.length >> 1);
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next_event_.type = Track::Event::IndexHole;
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return next_event_;
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}
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Storage::Time PCMSegmentEventSource::get_length()
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{
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return segment_.length_of_a_bit * segment_.number_of_bits;
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}
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Storage::Time PCMSegmentEventSource::seek_to(const Time &time_from_start)
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{
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// test for requested time being beyond the end
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Time length = get_length();
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if(time_from_start >= length)
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{
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next_event_.type = Track::Event::IndexHole;
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bit_pointer_ = segment_.number_of_bits;
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return length;
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}
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// if not beyond the end then make an initial assumption that the next thing encountered will be a flux transition
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next_event_.type = Track::Event::FluxTransition;
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// test for requested time being before the first bit
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Time half_bit_length = segment_.length_of_a_bit;
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half_bit_length.length >>= 1;
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if(time_from_start < half_bit_length)
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{
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bit_pointer_ = 0;
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Storage::Time zero;
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return zero;
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}
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// adjust for time to get to bit zero and determine number of bits in;
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// bit_pointer_ always records _the next bit_ that might trigger an event,
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// so should be one beyond the one reached by a seek.
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Time relative_time = time_from_start - half_bit_length;
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bit_pointer_ = 1 + (relative_time / segment_.length_of_a_bit).get_unsigned_int();
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// map up to the correct amount of time
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return half_bit_length + segment_.length_of_a_bit * (unsigned int)(bit_pointer_ - 1);
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}
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