zxtape.cpp

/*
 * zxtape.cpp
 *
 *  Created on: 25 mar 2016
 *      Author: wpk
 */
#include <fstream>
#include <iostream>
#include "zxtape.h"

using namespace std;

zxtape::zxtape(string filename) {
	ifstream file;
	file.open(filename.c_str(), std::ios::in | std::ios::binary);
	if (file.fail()) {
		throw ifstream::failure("Can't open TAP file");
	}
	file.seekg(0, std::ios_base::end);
	len = file.tellg();
	file.seekg(0);
	buf = new char[len];
	file.read(buf, len);
	file.close();
	reset();
}

void zxtape::newblock() {
	pos = 0;
	i_pos = 0;
	blockoffs += blocklen;
	if (blockoffs >= len) {
		state = END;
	} else {
		blockstate = PILOT;
		blocklen = * ( (uint16_t*) &buf[blockoffs]);
		blockoffs += 2;
	}
}
void zxtape::reset() {
	state = PAUSE;
	blockno = 0;
	blockoffs = 0;
	blocklen = 0;
	newblock();
	earr = false;
}

void zxtape::go() {
	state = RUNNING;
}

bool zxtape::bit() {
	return buf[blockoffs + (pos/8)] & (1 << (7 - (pos%8)));
}

void zxtape::flip() {
	earr = !earr;
}
void zxtape::update_ticks(uint32_t diff) {
	if (state != RUNNING) {
		return;
	}
	// A 'pulse' here is either a mark or a space, so 2 pulses makes a complete square wave cycle.
	// Pilot tone: before each block is a sequence of 8063 (header) or 3223 (data) pulses, each of length 2168 T-states.
	// Sync pulses: the pilot tone is followed by two sync pulses of 667 and 735 T-states resp.
	// A '0' bit is encoded as 2 pulses of 855 T-states each.
	// A '1' bit is encoded as 2 pulses of 1710 T-states each (ie. twice the length of a '0')
	i_pos += diff;
	switch (blockstate) {
	case PILOT:
		if (i_pos > 2168) {
			i_pos = 0;
			flip();
			if (++pos > 8000) {
				blockstate = SYNC;
				i_pos = 0;
				pos = 0;
			}
		}
		break;
	case SYNC:
		if (pos == 0) {
			if (i_pos > 667) {
				pos = 1;
				i_pos = 0;
				flip();
			}
		} else {
			if (i_pos > 735) {
				blockstate = DATA;
				tock = false;
				pos = 0;
				i_pos = 0;
				flip();
			}
		}
		break;
	case DATA: {
		uint32_t l = bit() ? 1705 : 850; // 1710 : 855;

		if (i_pos > 2*l) {
			flip();
			tock = false; // tick
			i_pos = 0;
			if (++pos == 8*blocklen) {
				newblock();
			}
		} else if (i_pos > l && !tock) {
			flip();
			tock = true;
		}
	}
	}

}
bool const zxtape::ear() {
	return earr;
}

zxtape::~zxtape() {
	delete[] buf;
}