mirror of
https://github.com/TomHarte/CLK.git
synced 2024-11-30 04:50:08 +00:00
114 lines
3.3 KiB
C++
114 lines
3.3 KiB
C++
//
|
||
// Bus.cpp
|
||
// Clock Signal
|
||
//
|
||
// Created by Thomas Harte on 10/02/2021.
|
||
// Copyright © 2021 Thomas Harte. All rights reserved.
|
||
//
|
||
|
||
#include "Bus.hpp"
|
||
|
||
using namespace Apple::ADB;
|
||
|
||
Bus::Bus(HalfCycles clock_speed) : half_cycles_to_microseconds_(1'000'000.0 / clock_speed.as<double>()) {}
|
||
|
||
void Bus::run_for(HalfCycles duration) {
|
||
time_in_state_ += duration;
|
||
time_since_get_state_ += duration;
|
||
}
|
||
|
||
void Bus::set_device_output(size_t device_id, bool output) {
|
||
// Modify the all-devices bus state.
|
||
bus_state_[device_id] = output;
|
||
|
||
// React to signal edges only; don't use get_state here to avoid
|
||
// endless recursion should any reactive devices set new output
|
||
// during the various calls made below.
|
||
const bool data_level = bus_state_.all();
|
||
if(data_level_ != data_level) {
|
||
data_level_ = data_level;
|
||
|
||
if(data_level) {
|
||
// This was a transition to high; classify what just happened according to
|
||
// the duration of the low period.
|
||
const double low_microseconds = time_in_state_.as<double>() * half_cycles_to_microseconds_;
|
||
|
||
// Low periods:
|
||
// (partly as adapted from the AN591 data sheet; otherwise from the IIgs reference manual)
|
||
//
|
||
// > 1040 µs reset
|
||
// 560–1040 µs attention
|
||
// < 50 µs 1
|
||
// 50–72 µs 0
|
||
// 300 µs service request
|
||
if(low_microseconds > 1040.0) {
|
||
for(auto device: devices_) {
|
||
device->adb_bus_did_observe_event(Event::Reset);
|
||
}
|
||
} else if(low_microseconds >= 560.0) {
|
||
for(auto device: devices_) {
|
||
device->adb_bus_did_observe_event(Event::Attention);
|
||
}
|
||
shift_register_ = 1;
|
||
start_target_ = 9; // Consume the stop bit before posting the next byte.
|
||
phase_ = Phase::AttentionCapture;
|
||
} else if(low_microseconds < 50.0) {
|
||
shift(1);
|
||
} else if(low_microseconds < 72.0) {
|
||
shift(0);
|
||
} else if(low_microseconds >= 291.0 && low_microseconds <= 309.0) {
|
||
for(auto device: devices_) {
|
||
device->adb_bus_did_observe_event(Event::ServiceRequest);
|
||
}
|
||
} else {
|
||
for(auto device: devices_) {
|
||
device->adb_bus_did_observe_event(Event::Unrecognised);
|
||
}
|
||
}
|
||
}
|
||
|
||
time_in_state_ = HalfCycles(0);
|
||
}
|
||
}
|
||
|
||
void Bus::shift(unsigned int value) {
|
||
shift_register_ = (shift_register_ << 1) | value;
|
||
|
||
// Trigger a byte whenever either:
|
||
// * a 'start bit' hits bit 8; or
|
||
// * if this was a command byte, wait for the stop bit (i.e. the start bit hits 9).
|
||
if(shift_register_ & (1 << start_target_)) {
|
||
for(auto device: devices_) {
|
||
device->adb_bus_did_observe_event(Event::Byte, uint8_t(shift_register_ >> (start_target_ - 8)));
|
||
}
|
||
|
||
// Expect a real start bit only if moving from attention capture to packet
|
||
// capture. Otherwise adopt an implied start bit.
|
||
shift_register_ = phase_ == Phase::PacketCapture;
|
||
start_target_ = 8;
|
||
phase_ = Phase::PacketCapture;
|
||
}
|
||
}
|
||
|
||
bool Bus::get_state() const {
|
||
const auto microseconds = time_since_get_state_.as<double>() * half_cycles_to_microseconds_;
|
||
time_since_get_state_ = HalfCycles(0);
|
||
|
||
const bool current_level = bus_state_.all();
|
||
for(auto device: devices_) {
|
||
device->advance_state(microseconds, current_level);
|
||
}
|
||
return bus_state_.all();
|
||
}
|
||
|
||
size_t Bus::add_device() {
|
||
const size_t id = next_device_id_;
|
||
++next_device_id_;
|
||
return id;
|
||
}
|
||
|
||
size_t Bus::add_device(Device *device) {
|
||
devices_.push_back(device);
|
||
return add_device();
|
||
}
|