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310c722cc0
The idea being that bus attachees need not all count time for themselves. They can be very plain finite state machines. New semantics are not yet implemented within the Bus. The plan is to do that, remove the internal counting of time within the NCR, then adjust the Target to be more explicitly stateful.
135 lines
4.1 KiB
C++
135 lines
4.1 KiB
C++
//
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// SCSI.hpp
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// Clock Signal
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//
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// Created by Thomas Harte on 12/08/2019.
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// Copyright © 2019 Thomas Harte. All rights reserved.
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//
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#ifndef SCSI_hpp
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#define SCSI_hpp
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#include <limits>
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#include <vector>
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#include "../../../ClockReceiver/ClockReceiver.hpp"
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#include "../../../ClockReceiver/ClockingHintSource.hpp"
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namespace SCSI {
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typedef int BusState;
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static const BusState DefaultBusState = 0;
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/*!
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SCSI bus state is encoded entirely within an int.
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Bits correlate mostly but not exactly to the real SCSI bus.
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TODO: validate levels below. The bus uses open collector logic,
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so active low needs to be respected.
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*/
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enum Line: BusState {
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/// Provides the value currently on the data lines.
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Data = 0xff,
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/// Parity of the data lines.
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Parity = 1 << 8,
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/// Set if the SEL line is currently selecting a target.
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/// Reset if it is selecting an initiator.
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SelectTarget = 1 << 9,
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/// Set to indicate an attention condition. Reset otherwise.
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Attention = 1 << 10,
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/// Set if control is on the bus. Reset if data is on the bus.
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Control = 1 << 11,
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/// Set if the bus is busy. Reset otherwise.
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Busy = 1 << 12,
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/// Set if acknowledging a data transfer request. Reset otherwise.
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Acknowledge = 1 << 13,
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/// Set if a bus reset is being requested. Reset otherwise.
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Reset = 1 << 14,
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/// Set if data is currently an input to the initiator. Reset if it is an output.
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Input = 1 << 15,
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/// Set during the message phase. Reset otherwise.
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Message = 1 << 16,
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/// Set if requesting a data transfer. Reset otherwise.
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Request = 1 << 17,
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};
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#define us(x) (x) / 1000000.0
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#define ns(x) (x) / 1000000000.0
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/// The minimum amount of time a SCSI device must wait after asserting ::Busy
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/// until the data bus can be inspected to see whether arbitration has been won.
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constexpr double ArbitrationDelay = us(1.7);
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/// The maximum amount of time a SCSI device can take from a detection that the
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/// bus is free until it asserts ::Busy and its ID for the purposes of arbitration.
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constexpr double BusSetDelay = us(1.1);
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/// The maximum amount of time a SCSI device is permitted to take to stop driving
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/// all bus signals after: (i) the release of ::Busy ushering in a bus free phase;
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/// or (ii) some other device has asserted ::Select during an arbitration phase.
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constexpr double BusClearDelay = ns(650.0);
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/// The minimum amount of time to wait for the bus to settle after changing
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/// "certain control signals". TODO: which?
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constexpr double BusSettleDelay = ns(450.0);
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/// The minimum amount of time a SCSI must wait from detecting that the bus is free
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/// and asserting ::Busy if starting an arbitration phase.
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constexpr double BusFreeDelay = ns(100.0);
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/// The minimum amount of time required for deskew of "certain signals". TODO: which?
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constexpr double DeskewDelay = ns(45.0);
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/// The minimum amount of time that reset must be held for.
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constexpr double ResetHoldTime = us(25.0);
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/// The maximum amount of time that propagation of a SCSI bus signal can take between
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/// any two devices.
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constexpr double CableSkew = ns(10.0);
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#undef ns
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#undef us
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class Bus {
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public:
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/*!
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Adds a device to the bus, returning the index it should use
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to refer to itself in subsequent calls to set_device_output.
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*/
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size_t add_device();
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/*!
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Sets the current output for @c device.
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*/
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void set_device_output(size_t device, BusState output);
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/*!
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@returns the current state of the bus.
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*/
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BusState get_state();
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struct Observer {
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/// Reports to an observer that the bus changed from a previous state to @c new_state,
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/// along with the time since that change was observed. The time is in seconds, and is
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/// intended for comparison with the various constants defined at namespace scope:
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/// ArbitrationDelay et al. Observers will be notified each time one of the thresholds
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/// defined by those constants is crossed.
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virtual void scsi_bus_did_change(Bus *, BusState new_state, double time_since_change) = 0;
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};
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/*!
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Adds an observer.
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*/
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void add_observer(Observer *);
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private:
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std::vector<BusState> device_states_;
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BusState state_ = DefaultBusState;
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std::vector<Observer *> observers_;
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};
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}
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#endif /* SCSI_hpp */
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