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249 lines
7.5 KiB
C++
249 lines
7.5 KiB
C++
//
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// ncr5380.cpp
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// Clock Signal
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//
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// Created by Thomas Harte on 10/08/2019.
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// Copyright © 2019 Thomas Harte. All rights reserved.
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//
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#include "ncr5380.hpp"
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#include "../../Outputs/Log.hpp"
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using namespace NCR::NCR5380;
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NCR5380::NCR5380(int clock_rate) :
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device_(bus_, 6),
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clock_rate_(clock_rate) {
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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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LOG("[SCSI 1] Initiator command register set: " << PADHEX(2) << int(value));
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initiator_command_ = value;
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bus_output_ &= ~(Line::Reset | Line::Acknowledge | Line::Busy | Line::SelectTarget | Line::Attention);
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if(value & 0x80) bus_output_ |= Line::Reset;
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if(value & 0x10) bus_output_ |= Line::Acknowledge;
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if(value & 0x08) bus_output_ |= Line::Busy;
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if(value & 0x04) bus_output_ |= Line::SelectTarget;
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if(value & 0x02) bus_output_ |= Line::Attention;
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/* bit 5 = differential enable if this were a 5381 */
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test_mode_ = value & 0x40;
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assert_data_bus_ = value & 0x01;
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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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if(mode_ & 1) {
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arbitration_in_progress_ = true;
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if(state_ == ExecutionState::None) {
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set_execution_state(ExecutionState::WatchingBusy);
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lost_arbitration_ = false;
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}
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} else {
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arbitration_in_progress_ = false;
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bus_output_ &= ~SCSI::Line::Busy;
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set_execution_state(ExecutionState::None);
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}
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break;
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case 3: {
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LOG("[SCSI 3] Set target command: " << PADHEX(2) << int(value));
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bus_output_ &= ~(Line::Request | Line::Message | Line::Control | Line::Input);
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if(value & 0x08) bus_output_ |= Line::Request;
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if(value & 0x04) bus_output_ |= Line::Message;
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if(value & 0x02) bus_output_ |= Line::Control;
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if(value & 0x01) bus_output_ |= Line::Input;
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} break;
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case 4:
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LOG("[SCSI 4] Set select enabled: " << PADHEX(2) << int(value));
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break;
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case 5:
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LOG("[SCSI 5] Start DMA send: " << PADHEX(2) << int(value));
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break;
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case 6:
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LOG("[SCSI 6] Start DMA target receive: " << PADHEX(2) << int(value));
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break;
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case 7:
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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 uint8_t(bus_.get_state());
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case 1:
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LOG("[SCSI 1] Initiator command register get: " << (arbitration_in_progress_ ? 'p' : '-') << (lost_arbitration_ ? 'l' : '-'));
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return
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// Bits repeated as they were set.
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(initiator_command_ & ~0x60) |
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// Arbitration in progress.
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(arbitration_in_progress_ ? 0x40 : 0x00) |
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// Lost arbitration.
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(lost_arbitration_ ? 0x20 : 0x00);
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case 2:
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LOG("[SCSI 2] Get mode");
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return mode_;
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case 3: {
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LOG("[SCSI 3] Get target command");
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const auto bus_state = bus_.get_state();
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return
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((bus_state & SCSI::Line::Request) ? 0x08 : 0x00) |
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((bus_state & SCSI::Line::Message) ? 0x04 : 0x00) |
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((bus_state & SCSI::Line::Control) ? 0x02 : 0x00) |
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((bus_state & SCSI::Line::Input) ? 0x01 : 0x00);
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}
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case 4: {
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const auto bus_state = bus_.get_state();
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const uint8_t result =
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((bus_state & SCSI::Line::Reset) ? 0x80 : 0x00) |
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((bus_state & SCSI::Line::Busy) ? 0x40 : 0x00) |
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((bus_state & SCSI::Line::Request) ? 0x20 : 0x00) |
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((bus_state & SCSI::Line::Message) ? 0x10 : 0x00) |
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((bus_state & SCSI::Line::Control) ? 0x08 : 0x00) |
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((bus_state & SCSI::Line::Input) ? 0x04 : 0x00) |
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((bus_state & SCSI::Line::SelectTarget) ? 0x02 : 0x00) |
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((bus_state & SCSI::Line::Parity) ? 0x01 : 0x00);
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LOG("[SCSI 4] Get current bus state: " << PADHEX(2) << int(result));
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return result;
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}
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case 5: {
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const auto bus_state = bus_.get_state();
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const uint8_t result =
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((bus_state & SCSI::Line::Attention) ? 0x02 : 0x00) |
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((bus_state & SCSI::Line::Acknowledge) ? 0x01 : 0x00);
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LOG("[SCSI 5] Get bus and status: " << PADHEX(2) << int(result));
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return result;
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}
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case 6:
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LOG("[SCSI 6] Get input data");
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return 0xff;
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case 7:
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LOG("[SCSI 7] Reset parity/interrupt");
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return 0xff;
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}
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return 0;
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}
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void NCR5380::run_for(Cycles cycles) {
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if(state_ == ExecutionState::None) return;
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++time_in_state_;
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switch(state_) {
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default: break;
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/*
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Official documentation:
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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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Personal notes:
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I'm discounting that "arbitratation is accomplished" opening, and assuming that what needs
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to happen is:
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(i) wait for BSY to be inactive;
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(ii) count 400 nsec;
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(iii) check that BSY and SEL are inactive.
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*/
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case ExecutionState::WatchingBusy:
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if(bus_.get_state() & SCSI::Line::Busy) {
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// Arbitration is lost only if a non-busy state had previously been observed.
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if(time_in_state_ > 1) {
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lost_arbitration_ = true;
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set_execution_state(ExecutionState::None);
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} else {
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time_in_state_ = 0;
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}
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} /* else {
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arbitration_in_progress_ = true;
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}*/
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// Check for having hit 400ns (more or less) since BSY was inactive.
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if(!lost_arbitration_ && time_in_state_ == int(int64_t(400) * int64_t(clock_rate_) / int64_t(1000000000))) {
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// arbitration_in_progress_ = false;
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if(bus_.get_state() & SCSI::Line::SelectTarget) {
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lost_arbitration_ = true;
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set_execution_state(ExecutionState::None);
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} else {
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bus_output_ &= ~SCSI::Line::Busy;
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set_execution_state(ExecutionState::None);
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}
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}
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break;
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}
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}
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void NCR5380::set_execution_state(ExecutionState state) {
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time_in_state_ = 0;
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state_ = state;
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update_clocking_observer();
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}
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ClockingHint::Preference NCR5380::preferred_clocking() {
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// Request real-time clocking if any sort of timed bus watching is ongoing,
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// given that there's no knowledge in here as to what clocking other devices
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// on the SCSI bus might be enjoying.
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return (state_ == ExecutionState::None) ? ClockingHint::Preference::None : ClockingHint::Preference::RealTime;
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}
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