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114 lines
3.3 KiB
C++
114 lines
3.3 KiB
C++
//
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// Bus.cpp
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// Clock Signal
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//
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// Created by Thomas Harte on 10/02/2021.
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// Copyright © 2021 Thomas Harte. All rights reserved.
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//
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#include "Bus.hpp"
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using namespace Apple::ADB;
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Bus::Bus(HalfCycles clock_speed) : half_cycles_to_microseconds_(1'000'000.0 / clock_speed.as<double>()) {}
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void Bus::run_for(HalfCycles duration) {
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time_in_state_ += duration;
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time_since_get_state_ += duration;
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}
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void Bus::set_device_output(size_t device_id, bool output) {
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// Modify the all-devices bus state.
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bus_state_[device_id] = output;
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// React to signal edges only; don't use get_state here to avoid
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// endless recursion should any reactive devices set new output
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// during the various calls made below.
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const bool data_level = bus_state_.all();
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if(data_level_ != data_level) {
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data_level_ = data_level;
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if(data_level) {
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// This was a transition to high; classify what just happened according to
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// the duration of the low period.
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const double low_microseconds = time_in_state_.as<double>() * half_cycles_to_microseconds_;
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// Low periods:
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// (partly as adapted from the AN591 data sheet; otherwise from the IIgs reference manual)
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//
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// > 1040 µs reset
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// 560–1040 µs attention
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// < 50 µs 1
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// 50–72 µs 0
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// 300 µs service request
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if(low_microseconds > 1040.0) {
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for(auto device: devices_) {
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device->adb_bus_did_observe_event(Event::Reset);
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}
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} else if(low_microseconds >= 560.0) {
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for(auto device: devices_) {
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device->adb_bus_did_observe_event(Event::Attention);
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}
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shift_register_ = 1;
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start_target_ = 9; // Consume the stop bit before posting the next byte.
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phase_ = Phase::AttentionCapture;
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} else if(low_microseconds < 50.0) {
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shift(1);
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} else if(low_microseconds < 72.0) {
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shift(0);
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} else if(low_microseconds >= 291.0 && low_microseconds <= 309.0) {
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for(auto device: devices_) {
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device->adb_bus_did_observe_event(Event::ServiceRequest);
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}
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} else {
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for(auto device: devices_) {
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device->adb_bus_did_observe_event(Event::Unrecognised);
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}
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}
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}
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time_in_state_ = HalfCycles(0);
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}
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}
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void Bus::shift(unsigned int value) {
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shift_register_ = (shift_register_ << 1) | value;
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// Trigger a byte whenever either:
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// * a 'start bit' hits bit 8; or
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// * if this was a command byte, wait for the stop bit (i.e. the start bit hits 9).
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if(shift_register_ & (1 << start_target_)) {
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for(auto device: devices_) {
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device->adb_bus_did_observe_event(Event::Byte, uint8_t(shift_register_ >> (start_target_ - 8)));
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}
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// Expect a real start bit only if moving from attention capture to packet
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// capture. Otherwise adopt an implied start bit.
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shift_register_ = phase_ == Phase::PacketCapture;
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start_target_ = 8;
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phase_ = Phase::PacketCapture;
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}
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}
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bool Bus::get_state() const {
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const auto microseconds = time_since_get_state_.as<double>() * half_cycles_to_microseconds_;
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time_since_get_state_ = HalfCycles(0);
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const bool current_level = bus_state_.all();
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for(auto device: devices_) {
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device->advance_state(microseconds, current_level);
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}
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return bus_state_.all();
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}
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size_t Bus::add_device() {
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const size_t id = next_device_id_;
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++next_device_id_;
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return id;
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}
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size_t Bus::add_device(Device *device) {
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devices_.push_back(device);
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return add_device();
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}
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