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https://github.com/TomHarte/CLK.git
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Starts thinking out the mechanics of emulating a SCSI-1 bus.
This commit is contained in:
Thomas Harte
parent
0f67e490e8
commit
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34
Components/5380/SCSI.cpp
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34
Components/5380/SCSI.cpp
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@ -0,0 +1,34 @@
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//
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// SCSI.cpp
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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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#include "SCSI.hpp"
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using namespace SCSI;
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size_t Bus::add_device() {
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const auto slot = device_states_.size();
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device_states_.push_back(DefaultBusState);
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return slot;
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}
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void Bus::set_device_output(size_t device, BusState output) {
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device_states_[device] = output;
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state_is_valid_ = false;
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}
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BusState Bus::get_state() {
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if(!state_is_valid_) return state_;
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state_is_valid_ = true;
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state_ = DefaultBusState;
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for(auto state: device_states_) {
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state_ &= state;
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}
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return state_;
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}
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79
Components/5380/SCSI.hpp
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79
Components/5380/SCSI.hpp
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@ -0,0 +1,79 @@
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//
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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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namespace SCSI {
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typedef int BusState;
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static const BusState DefaultBusState = std::numeric_limits<BusState>::max();
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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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/// Reset to indicate an attention condition. Set 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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/// Reset if the bus is busy. Set otherwise.
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Busy = 1 << 12,
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/// Reset if acknowledging a data transfer request. Set otherwise.
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Acknowledge = 1 << 13,
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/// Reset if a bus reset is being requested. Set otherwise.
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Reset = 1 << 14,
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/// Set if data is currently input. 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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MessagePhase = 1 << 16
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};
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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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private:
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std::vector<BusState> device_states_;
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BusState state_ = DefaultBusState;
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bool state_is_valid_ = false;
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};
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}
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#endif /* SCSI_hpp */
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@ -12,19 +12,56 @@
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using namespace NCR::NCR5380;
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NCR5380::NCR5380() {
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device_id_ = bus_.add_device();
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}
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void NCR5380::write(int address, uint8_t value) {
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using Line = SCSI::Line;
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switch(address & 7) {
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case 0:
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LOG("[SCSI 0] Set current SCSI bus state to " << PADHEX(2) << int(value));
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data_bus_ = value;
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break;
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case 1:
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case 1: {
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LOG("[SCSI 1] Initiator command register set: " << PADHEX(2) << int(value));
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break;
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initiator_command_ = value;
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SCSI::BusState mask = SCSI::DefaultBusState;
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if(value & 0x80) mask &= ~Line::Reset;
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test_mode_ = !!(value & 0x40);
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/* bit 5 = differential enable if this were a 5381 */
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if(value & 0x10) mask &= ~Line::Acknowledge;
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if(value & 0x08) mask &= ~Line::Busy;
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if(value & 0x04) mask &= ~Line::SelectTarget;
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if(value & 0x02) mask &= ~Line::Attention;
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assert_data_bus_ = (value & 0x01);
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bus_output_ = (bus_output_ | Line::Reset | Line::Acknowledge | Line::Busy | Line::SelectTarget | Line::Attention) & mask;
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} break;
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case 2:
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LOG("[SCSI 2] Set mode: " << PADHEX(2) << int(value));
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mode_ = value;
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// bit 7: 1 = use block mode DMA mode (if DMA mode is also enabled)
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// bit 6: 1 = be a SCSI target; 0 = be an initiator
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// bit 5: 1 = check parity
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// bit 4: 1 = generate an interrupt if parity checking is enabled and an error is found
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// bit 3: 1 = generate an interrupt when an EOP is received from the DMA controller
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// bit 2: 1 = generate an interrupt and reset low 6 bits of register 1 if an unexpected loss of Line::Busy occurs
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// bit 1: 1 = use DMA mode
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// bit 0: 1 = begin arbitration mode (device ID should be in register 0)
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/*
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Arbitration is accomplished using a bus-free filter to continuously monitor BSY.
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If BSY remains inactive for at least 400 nsec then the SCSI bus is considered free
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and arbitration may begin. Arbitration will begin if the bus is free, SEL is inactive
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and the ARBITRATION bit (port 2, bit 0) is active. Once arbitration has begun
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(BSY asserted), an arbitration delay of 2.2 /Lsec must elapse before the data bus
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can be examined to deter- mine if arbitration has been won. This delay must be
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implemented in the controlling software driver.
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*/
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break;
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case 3:
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@ -47,17 +84,32 @@ void NCR5380::write(int address, uint8_t value) {
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LOG("[SCSI 7] Start DMA initiator receive: " << PADHEX(2) << int(value));
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break;
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}
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// Data is output only if the data bus is asserted.
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if(assert_data_bus_) {
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bus_output_ &= data_bus_;
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} else {
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bus_output_ |= SCSI::Line::Data;
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}
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// In test mode, still nothing is output. Otherwise throw out
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// the current value of bus_output_.
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if(test_mode_) {
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bus_.set_device_output(device_id_, SCSI::DefaultBusState);
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} else {
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bus_.set_device_output(device_id_, bus_output_);
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}
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}
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uint8_t NCR5380::read(int address) {
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switch(address & 7) {
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case 0:
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LOG("[SCSI 0] Get current SCSI bus state");
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return 0xff;
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return uint8_t(bus_.get_state());
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case 1:
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LOG("[SCSI 1] Initiator command register get");
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return 0xff;
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return initiator_command_;
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case 2:
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LOG("[SCSI 2] Get mode");
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@ -11,6 +11,10 @@
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#include <cstdint>
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#include "SCSI.hpp"
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#include "../../ClockReceiver/ClockReceiver.hpp"
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namespace NCR {
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namespace NCR5380 {
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@ -19,14 +23,40 @@ namespace NCR5380 {
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*/
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class NCR5380 {
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public:
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NCR5380();
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/*! Writes @c value to @c address. */
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void write(int address, uint8_t value);
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/*! Reads from @c address. */
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uint8_t read(int address);
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/*!
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As per its design manual:
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"The NCR 5380 is a clockless device. Delays such as bus
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free delay, bus set delay and bus settle delay are
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implemented using gate delays."
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Therefore this fictitious implementation of an NCR5380 needs
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a way to track time even though the real one doesn't take in
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a clock. This is provided by `run_for`.
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Nevertheless, the clocking doesn't need to be very precise.
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Please provide a clock that is close to 200,000 Hz.
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*/
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void run_for(Cycles);
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private:
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SCSI::Bus bus_;
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size_t device_id_;
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SCSI::BusState bus_output_ = SCSI::DefaultBusState;
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uint8_t mode_ = 0xff;
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uint8_t initiator_command_ = 0xff;
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uint8_t data_bus_ = 0xff;
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bool test_mode_ = false;
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bool assert_data_bus_ = false;
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};
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}
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@ -300,6 +300,8 @@
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4B89453F201967B4007DE474 /* StaticAnalyser.cpp in Sources */ = {isa = PBXBuildFile; fileRef = 4B894517201967B4007DE474 /* StaticAnalyser.cpp */; };
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4B89BCFC23024BB500EA0782 /* SCSI.cpp in Sources */ = {isa = PBXBuildFile; fileRef = 4B89BCFA23024BB500EA0782 /* SCSI.cpp */; };
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4B89BCFD23024BB500EA0782 /* SCSI.cpp in Sources */ = {isa = PBXBuildFile; fileRef = 4B89BCFA23024BB500EA0782 /* SCSI.cpp */; };
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@ -1057,6 +1059,8 @@
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4B894516201967B4007DE474 /* StaticAnalyser.cpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.cpp; path = StaticAnalyser.cpp; sourceTree = "<group>"; };
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4B894517201967B4007DE474 /* StaticAnalyser.cpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.cpp; path = StaticAnalyser.cpp; sourceTree = "<group>"; };
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4B894540201967D6007DE474 /* Machines.hpp */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.cpp.h; path = Machines.hpp; sourceTree = "<group>"; };
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@ -3327,6 +3331,8 @@
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children = (
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4BDACBEA22FFA5D20045EF7E /* ncr5380.cpp */,
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4BDACBEB22FFA5D20045EF7E /* ncr5380.hpp */,
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4B89BCFA23024BB500EA0782 /* SCSI.cpp */,
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4B89BCFB23024BB500EA0782 /* SCSI.hpp */,
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);
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path = 5380;
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sourceTree = "<group>";
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@ -4037,6 +4043,7 @@
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4B8318B822D3E566006DB630 /* IWM.cpp in Sources */,
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4B0333B02094081A0050B93D /* AppleDSK.cpp in Sources */,
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4B894535201967B4007DE474 /* AddressMapper.cpp in Sources */,
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4B89BCFD23024BB500EA0782 /* SCSI.cpp in Sources */,
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4B055AD41FAE9B0B0060FFFF /* Oric.cpp in Sources */,
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4B055A921FAE85B50060FFFF /* PRG.cpp in Sources */,
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4B055AAF1FAE85FD0060FFFF /* UnformattedTrack.cpp in Sources */,
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@ -4194,6 +4201,7 @@
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4B894528201967B4007DE474 /* Disk.cpp in Sources */,
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4BBB70A4202011C2002FE009 /* MultiMediaTarget.cpp in Sources */,
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||||
4B89453A201967B4007DE474 /* StaticAnalyser.cpp in Sources */,
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4B89BCFC23024BB500EA0782 /* SCSI.cpp in Sources */,
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||||
4BB697CB1D4B6D3E00248BDF /* TimedEventLoop.cpp in Sources */,
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4BDACBEC22FFA5D20045EF7E /* ncr5380.cpp in Sources */,
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4B54C0C21F8D91CD0050900F /* Keyboard.cpp in Sources */,
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||||
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||||
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