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171 lines
4.2 KiB
C++
171 lines
4.2 KiB
C++
//
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// Keyboard.h
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// Clock Signal
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//
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// Created by Thomas Harte on 08/05/2019.
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// Copyright © 2019 Thomas Harte. All rights reserved.
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//
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#ifndef Keyboard_hpp
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#define Keyboard_hpp
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namespace Apple {
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namespace Macintosh {
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class Keyboard {
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public:
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void set_input(bool data) {
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switch(mode_) {
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case Mode::Waiting:
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/*
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"Only the computer can initiate communication over the keyboard lines. When the computer and keyboard
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are turned on, the computer is in charge of the keyboard interface and the keyboard is passive. The
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computer signals that it is ready to begin communication by pulling the Keyboard Data line low."
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*/
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if(!data) {
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mode_ = Mode::AcceptingCommand;
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phase_ = 0;
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command_ = 0;
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}
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break;
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case Mode::AcceptingCommand:
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/* Note value, so that it can be latched upon a clock transition. */
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data_input_ = data;
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break;
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case Mode::AwaitingEndOfCommand:
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/*
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The last bit of the command leaves the Keyboard Data line low; the computer then indicates that it is ready
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to receive the keyboard's response by setting the Keyboard Data line high.
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*/
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if(data) {
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mode_ = Mode::PerformingCommand;
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phase_ = 0;
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}
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break;
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default:
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case Mode::SendingResponse:
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/* This line isn't currently an input; do nothing. */
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break;
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}
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}
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bool get_clock() {
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return clock_output_;
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}
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bool get_data() {
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return !!(response_ & 0x80);
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}
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/*!
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The keyboard expects ~10 µs-frequency ticks, i.e. a clock rate of just around 100 kHz.
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*/
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void run_for(HalfCycles cycle) {
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switch(mode_) {
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default:
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case Mode::AwaitingEndOfCommand:
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case Mode::Waiting: return;
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case Mode::AcceptingCommand: {
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/*
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"When the computer is sending data to the keyboard, the keyboard transmits eight cycles of 400 µS each (180 µS low,
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220 µS high) on the Keyboard Clock line. On the falling edge of each keyboard clock cycle, the Macintosh Plus places
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a data bit on the data line and holds it there for 400 µS. The keyboard reads the data bit 80 µS after the rising edge
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of the Keyboard Clock signal."
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*/
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const auto offset = phase_ % 40;
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clock_output_ = offset >= 18;
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if(offset == 26) {
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command_ = (command_ << 1) | (data_input_ ? 1 : 0);
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}
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++phase_;
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if(phase_ == 8*40) {
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mode_ = Mode::AwaitingEndOfCommand;
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phase_ = 0;
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clock_output_ = false;
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}
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} break;
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case Mode::PerformingCommand: {
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response_ = perform_command(command_);
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// Inquiry has a 0.25-second timeout; everything else is instant.
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++phase_;
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if(phase_ == 25000 || command_ != 0x10 || response_ != 0x7b) {
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mode_ = Mode::SendingResponse;
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phase_ = 0;
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}
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} break;
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case Mode::SendingResponse: {
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/*
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"When sending data to the computer, the keyboard transmits eight cycles of 330 µS each (160 µS low, 170 µS high)
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on the normally high Keyboard Clock line. It places a data bit on the data line 40 µS before the falling edge of each
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clock cycle and maintains it for 330 µS. The VIA in the computer latches the data bit into its shift register on the
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rising edge of the Keyboard Clock signal."
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*/
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const auto offset = phase_ % 33;
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clock_output_ = offset >= 16;
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if(offset == 29) {
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response_ <<= 1;
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}
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++phase_;
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if(phase_ == 8*33) {
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clock_output_ = false;
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mode_ = Mode::Waiting;
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phase_ = 0;
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}
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} break;
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}
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}
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private:
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int perform_command(int command) {
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switch(command) {
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case 0x10: // Inquiry.
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break;
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case 0x14: // Instant.
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break;
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case 0x16: // Model number.
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return
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0x01 | // b0: always 1
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(1 << 1) | // keyboard model number
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(1 << 4); // next device number
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// (b7 not set => no next device)
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case 0x36: // Test
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return 0x7d; // 0x7d = ACK, 0x77 = not ACK.
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}
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return 0x7b; // No key transition.
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}
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enum class Mode {
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Waiting,
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AcceptingCommand,
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AwaitingEndOfCommand,
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SendingResponse,
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PerformingCommand
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} mode_ = Mode::Waiting;
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int phase_ = 0;
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int command_ = 0;
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int response_ = 0;
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bool data_input_ = false;
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bool clock_output_ = false;
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};
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}
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}
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#endif /* Keyboard_h */
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