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159 lines
3.6 KiB
C++
159 lines
3.6 KiB
C++
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//
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// RealTimeClock.hpp
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// Clock Signal
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//
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// Created by Thomas Harte on 07/05/2019.
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// Copyright © 2019 Thomas Harte. All rights reserved.
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//
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#ifndef RealTimeClock_hpp
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#define RealTimeClock_hpp
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namespace Apple {
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namespace Macintosh {
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/*!
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Models the storage component of Apple's real-time clock.
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Since tracking of time is pushed to this class, it is assumed
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that whomever is translating real time into emulated time
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will notify the VIA of a potential interrupt.
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*/
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class RealTimeClock {
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public:
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/*!
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Advances the clock by 1 second.
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The caller should also notify the VIA.
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*/
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void update() {
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for(int c = 0; c < 4; ++c) {
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++seconds_[c];
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if(seconds_[c]) break;
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}
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}
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/*!
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Sets the current clock and data inputs to the clock.
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*/
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void set_input(bool clock, bool data) {
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/*
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Documented commands:
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z0000001 Seconds register 0 (lowest order byte)
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z0000101 Seconds register 1
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z0001001 Seconds register 2
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z0001101 Seconds register 3
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00110001 Test register (write only)
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00110101 Write-protect register (write only)
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z010aa01 RAM addresses 0x10 - 0x13
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z1aaaa01 RAM addresses 0x00 – 0x0f
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z = 1 => a read; z = 0 => a write.
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The top bit of the write-protect register enables (0) or disables (1)
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writes to other locations.
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All the documentation says about the test register is to set the top
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two bits to 0 for normal operation. Abnormal operation is undefined.
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The data line is valid when the clock transitions to level 0.
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*/
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if(clock && !previous_clock_) {
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// Shift into the command_ register, no matter what.
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command_ = uint16_t((command_ << 1) | (data ? 1 : 0));
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result_ <<= 1;
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// Increment phase.
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++phase_;
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// When phase hits 8, inspect the command.
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// If it's a read, prepare a result.
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if(phase_ == 8) {
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if(command_ & 0x80) {
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// A read.
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const auto address = (command_ >> 2) & 0x1f;
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// Begin pessimistically.
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result_ = 0xff;
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if(address < 4) {
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result_ = seconds_[address];
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} else if(address >= 0x10) {
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result_ = data_[address & 0xf];
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} else if(address >= 0x8 && address < 0xb) {
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result_ = data_[0x10 + (address & 0x3)];
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}
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}
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}
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// If phase hits 16 and this was a read command,
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// just stop. If it was a write command, do the
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// actual write.
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if(phase_ == 16) {
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if(!(command_ & 0x8000)) {
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// A write.
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const auto address = (command_ >> 10) & 0x1f;
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const uint8_t value = uint8_t(command_ & 0xff);
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// First test: is this to the write-protect register?
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if(address == 0xd) {
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write_protect_ = value;
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}
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// No other writing is permitted if the write protect
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// register won't allow it.
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if(!(write_protect_ & 0x80)) {
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if(address < 4) {
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seconds_[address] = value;
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} else if(address >= 0x10) {
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data_[address & 0xf] = value;
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} else if(address >= 0x8 && address < 0xb) {
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data_[0x10 + (address & 0x3)] = value;
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}
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}
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}
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// A phase of 16 always ends the command, so reset here.
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abort();
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}
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}
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previous_clock_ = clock;
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}
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/*!
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Reads the current data output level from the clock.
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*/
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bool get_data() {
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return !!(result_ & 0x80);
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}
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/*!
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Announces that a serial command has been aborted.
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*/
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void abort() {
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result_ = 0;
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phase_ = 0;
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command_ = 0;
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}
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private:
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uint8_t data_[0x14];
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uint8_t seconds_[4];
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uint8_t write_protect_;
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int phase_ = 0;
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uint16_t command_;
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uint8_t result_ = 0;
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bool previous_clock_ = false;
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};
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}
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}
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#endif /* RealTimeClock_hpp */
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