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95 lines
2.7 KiB
C++
95 lines
2.7 KiB
C++
//
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// DiskII.cpp
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// Clock Signal
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//
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// Created by Thomas Harte on 20/04/2018.
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// Copyright © 2018 Thomas Harte. All rights reserved.
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//
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#include "DiskII.hpp"
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#include <cstdio>
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using namespace Apple;
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void DiskII::set_control(Control control, bool on) {
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printf("Set control %d %s\n", control, on ? "on" : "off");
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// TODO: seeking, motor control.
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}
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void DiskII::set_mode(Mode mode) {
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printf("Set mode %d\n", mode);
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inputs_ = (inputs_ & ~0x08) | ((mode == Mode::Write) ? 0x2: 0x0);
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}
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void DiskII::select_drive(int drive) {
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printf("Select drive %d\n", drive);
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// TODO: select a drive.
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}
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void DiskII::set_data_register(uint8_t value) {
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printf("Set data register (?)\n");
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inputs_ |= 0x1;
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data_register_ = value;
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}
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uint8_t DiskII::get_shift_register() {
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printf("[%02x] ", shift_register_);
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inputs_ &= ~0x1;
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return shift_register_;
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}
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void DiskII::run_for(const Cycles cycles) {
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/*
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... address the P6 ROM with an index byte built up as:
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+-------+-------+-------+-------+-------+-------+-------+-------+
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| STATE | STATE | STATE | PULSE | Q7 | Q6 | SR | STATE |
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| bit 0 | bit 2 | bit 3 | | | | MSB | bit 1 |
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+-------+-------+-------+-------+-------+-------+-------+-------+
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7 6 5 4 3 2 1 0
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...
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The bytes in the P6 ROM has the high four bits reversed compared to the BAPD charts, so you will have to reverse them after fetching the byte.
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*/
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// TODO: optimise the resting state.
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int integer_cycles = cycles.as_int();
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while(integer_cycles--) {
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const int address =
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(inputs_ << 2) |
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((shift_register_&0x80) >> 6) |
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((state_&0x2) >> 1) |
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((state_&0x1) << 7) |
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((state_&0x4) << 4) |
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((state_&0x8) << 2);
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// TODO: add pulse state in bit 4.
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const uint8_t update = state_machine_[static_cast<std::size_t>(address)];
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state_ = update >> 4;
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state_ = ((state_ & 0x8) ? 0x1 : 0x0) | ((state_ & 0x4) ? 0x2 : 0x0) | ((state_ & 0x2) ? 0x4 : 0x0) | ((state_ & 0x1) ? 0x8 : 0x0);
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uint8_t command = update & 0xf;
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switch(command) {
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case 0x0: shift_register_ = 0; break; // clear
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case 0x9: shift_register_ = static_cast<uint8_t>(shift_register_ << 1); break; // shift left, bringing in a zero
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case 0xd: shift_register_ = static_cast<uint8_t>((shift_register_ << 1) | 1); break; // shift left, bringing in a one
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case 0xb: shift_register_ = data_register_; break; // load
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case 0xa:
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shift_register_ = (shift_register_ >> 1) | (is_write_protected() ? 0x80 : 0x00);
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break; // shift right, bringing in write protected status
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default: break;
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}
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}
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}
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bool DiskII::is_write_protected() {
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return true;
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}
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void DiskII::set_state_machine(const std::vector<uint8_t> &state_machine) {
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state_machine_ = state_machine;
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// TODO: shuffle ordering here?
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}
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