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86 lines
2.9 KiB
C++
86 lines
2.9 KiB
C++
//
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// ClockingHintSource.h
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// Clock Signal
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//
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// Created by Thomas Harte on 20/08/2017.
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// Copyright 2017 Thomas Harte. All rights reserved.
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//
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#pragma once
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namespace ClockingHint {
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enum class Preference {
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/// The component doesn't currently require a clock signal.
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None,
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/// The component can be clocked only immediate prior to (explicit) accesses.
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JustInTime,
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/// The component require real-time clocking.
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RealTime
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};
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class Source;
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struct Observer {
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/// Called to inform an observer that the component @c component has changed its clocking requirements.
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virtual void set_component_prefers_clocking(Source *component, Preference clocking) = 0;
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};
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/*!
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An clocking hint source is any component that can provide hints as to the type of
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clocking required for accurate emulation. A disk controller is an archetypal example.
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Types of clocking are:
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- none:
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a component that acts and reacts to direct contact but does not have a state that autonomously evolves.
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E.g. a ROM, RAM, or some kinds of disk controller when not in the process of performing a command.
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- just-in-time:
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a component that has an evolving state but can receive clock updates only immediately before a
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direct contact. This is possibly the most common kind of component.
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- real-time:
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a component that needs to be clocked in 'real time' (i.e. in terms of the emulated machine). For example
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so that it can announce an interrupt at the proper moment, because it is monitoring some aspect of
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the machine rather than waiting to be called upon, or because there's some other non-obvious relationship
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at play.
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A clocking hint source can signal changes in preferred clocking to an observer.
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This is intended to allow for performance improvements to machines with components that can be messaged selectively.
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The observer callout is virtual so the intended use case is that a machine holds a component that might go through
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periods of different clocking requirements.
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Transitions should be sufficiently infrequent that a virtual call to announce them costs little enough that
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the saved or deferred ::run_fors add up to a substantial amount.
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The hint provided is just that: a hint. Owners may perform ::run_for at a greater frequency.
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*/
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class Source {
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public:
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/// Registers @c observer as the new clocking observer.
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void set_clocking_hint_observer(Observer *observer) {
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observer_ = observer;
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update_clocking_observer();
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}
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/// @returns the current preferred clocking strategy.
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virtual Preference preferred_clocking() const = 0;
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private:
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Observer *observer_ = nullptr;
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protected:
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/*!
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Provided for subclasses; call this whenever the clocking preference might have changed.
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This will notify the observer if there is one.
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*/
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void update_clocking_observer() {
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if(!observer_) return;
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observer_->set_component_prefers_clocking(this, preferred_clocking());
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}
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};
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}
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