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114 lines
3.9 KiB
C++
114 lines
3.9 KiB
C++
//
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// Card.h
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// Clock Signal
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//
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// Created by Thomas Harte on 23/04/2018.
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// Copyright 2018 Thomas Harte. All rights reserved.
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//
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#ifndef Card_h
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#define Card_h
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#include "../../Processors/6502/6502.hpp"
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#include "../../ClockReceiver/ClockReceiver.hpp"
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#include "../../Activity/Observer.hpp"
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namespace AppleII {
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/*!
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This provides a small subset of the interface offered to cards installed in
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an Apple II, oriented pragmatically around the cards that are implemented.
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The main underlying rule is as it is elsewhere in the emulator: no
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_inaccurate_ simplifications — no provision of information that shouldn't
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actually commute, no interfaces that say they do one thing but which by both
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both sides are coupled through an unwritten understanding of abuse.
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Special notes:
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Devices that announce a select constraint, being interested in acting only
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when their IO or Device select is active will receive just-in-time @c run_for
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notifications, as well as being updated at the end of each of the Apple's
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@c run_for periods, prior to a @c flush.
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Devices that do not announce a select constraint will prima facie receive a
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@c perform_bus_operation every cycle. They'll also receive a @c flush.
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It is **highly** recomended that such devices also implement @c Sleeper
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as they otherwise prima facie require a virtual method call every
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single cycle.
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*/
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class Card {
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public:
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enum Select: int {
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None = 0, // No select line is active
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IO = 1 << 0, // IO select is active
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Device = 1 << 1, // Device select is active
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};
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/*!
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Advances time by @c cycles, of which @c stretches were stretched.
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This is posted only to cards that announced a select constraint. Cards with
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no constraints, that want to be informed of every machine cycle, will receive
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a call to perform_bus_operation every cycle and should use that for time keeping.
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*/
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virtual void run_for(Cycles half_cycles, int stretches) {}
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/// Requests a flush of any pending audio or video output.
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virtual void flush() {}
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/*!
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Performs a bus operation.
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@param select The state of the card's select lines: indicates whether the Apple II
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thinks this card should respond as though this were an IO access, a Device access,
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or it thinks that the card shouldn't respond.
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@param is_read @c true if this is a read cycle; @c false otherwise.
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@param address The current value of the address bus.
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@param value A pointer to the value of the data bus, not accounting input from cards.
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If this is a read cycle, the card is permitted to replace this value with the value
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output by the card, if any. If this is a write cycle, the card should only read
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this value.
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*/
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virtual void perform_bus_operation(Select select, bool is_read, uint16_t address, uint8_t *value) = 0;
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/*!
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Returns the type of bus selects this card is actually interested in.
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As specified, the default is that cards will ask to receive perform_bus_operation
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only when their select lines are active.
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There's a substantial caveat here: cards that register to receive @c None
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will receive a perform_bus_operation every cycle. To reduce the number of
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virtual method calls, they **will not** receive run_for. run_for will propagate
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only to cards that register for IO and/or Device accesses only.
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*/
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int get_select_constraints() {
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return select_constraints_;
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}
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/*! Cards may supply a target for activity observation if desired. */
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virtual void set_activity_observer(Activity::Observer *observer) {}
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struct Delegate {
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virtual void card_did_change_select_constraints(Card *card) = 0;
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};
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void set_delegate(Delegate *delegate) {
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delegate_ = delegate;
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}
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protected:
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int select_constraints_ = IO | Device;
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Delegate *delegate_ = nullptr;
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void set_select_constraints(int constraints) {
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if(constraints == select_constraints_) return;
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select_constraints_ = constraints;
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if(delegate_) delegate_->card_did_change_select_constraints(this);
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}
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};
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}
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#endif /* Card_h */
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