livingcomputermuseum.ContrAlto/Contralto/CPU/Tasks/TridentTask.cs

/*  
    This file is part of ContrAlto.

    ContrAlto is free software: you can redistribute it and/or modify
    it under the terms of the GNU Affero General Public License as published by
    the Free Software Foundation, either version 3 of the License, or
    (at your option) any later version.

    ContrAlto is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU Affero General Public License for more details.

    You should have received a copy of the GNU Affero General Public License
    along with ContrAlto.  If not, see <http://www.gnu.org/licenses/>.
*/

using Contralto.IO;
using System;

namespace Contralto.CPU
{
    public partial class AltoCPU
    {
        /// <summary>
        /// TridentTask implements the microcode special functions for the Trident
        /// disk controller (for both the read and write tasks).
        /// </summary>
        private sealed class TridentTask : Task
        {
            public TridentTask(AltoCPU cpu, bool input) : base(cpu)
            {
                _taskType = input ? TaskType.TridentInput : TaskType.TridentOutput;
                _wakeup = false;

                _tridentController = cpu._system.TridentController;

                // Both Trident tasks are RAM-related
                _ramTask = true;
            }

            public override void SoftReset()
            {
                //
                // Stop the controller.
                //
                _tridentController.Stop();

                base.SoftReset();
            }

            protected override ushort GetBusSource(MicroInstruction instruction)
            {
                //
                // The Trident tasks are wired to be RAM-enabled tasks so they can use
                // S registers.
                // This code is stolen from the Emulator task; we should REALLY refactor this
                // since both this and the Orbit Task need it.
                //
                EmulatorBusSource ebs = (EmulatorBusSource)instruction.BS;

                switch (ebs)
                {
                    case EmulatorBusSource.ReadSLocation:
                        if (instruction.RSELECT != 0)
                        {
                            return _cpu._s[_rb][instruction.RSELECT];
                        }
                        else
                        {
                            // "...when reading data from the S registers onto the processor bus,
                            //  the RSELECT value 0 causes the current value of the M register to
                            //  appear on the bus..."
                            return _cpu._m;
                        }

                    case EmulatorBusSource.LoadSLocation:
                        // "When an S register is being loaded from M, the processor bus receives an
                        // undefined value rather than being set to zero."
                        _loadS = true;
                        return 0xffff;       // Technically this is an "undefined value," we're defining it as -1.

                    default:
                        throw new InvalidOperationException(String.Format("Unhandled bus source {0}", instruction.BS));
                }
            }

            protected override void ExecuteSpecialFunction2PostBusSource(MicroInstruction instruction)
            {
                TridentF2 tf2 = (TridentF2)instruction.F2;

                switch (tf2)
                {
                    case TridentF2.ReadKDTA:
                        //
                        // <-KDTA is actually MD<- (SF 6), repurposed to gate disk data onto the bus
                        // iff BS is None.  Otherwise it behaves like a normal MD<-.  We'll let
                        // the normal Task implementation handle the actual MD<- operation.
                        //
                        if (instruction.BS == BusSource.None)
                        {
                            // _busData at this point should be 0xffff.  We could technically
                            // just directly assign the bits...
                            _busData &= _tridentController.KDTA;
                        }
                        break;

                    case TridentF2.STATUS:
                        _busData &= _tridentController.STATUS;
                        break;

                    case TridentF2.EMPTY:
                        _tridentController.WaitForEmpty();
                        break;

                }
            }

            protected override void ExecuteSpecialFunction2(MicroInstruction instruction)
            {
                TridentF2 tf2 = (TridentF2)instruction.F2;

                switch (tf2)
                {
                    case TridentF2.KTAG:
                        _tridentController.TagInstruction(_busData);
                        break;

                    case TridentF2.WriteKDTA:
                        _tridentController.KDTA = _busData;
                        break;

                    case TridentF2.WAIT:
                    case TridentF2.WAIT2:
                        // Identical to BLOCK
                        this.BlockTask();
                        break;

                    case TridentF2.RESET:
                        _tridentController.ControllerReset();
                        break;

                    case TridentF2.STATUS:
                    case TridentF2.EMPTY:
                        // Handled in PostBusSource override.
                        break;

                    default:
                        throw new InvalidOperationException(String.Format("Unhandled trident special function 2 {0}", tf2));
                }
            }

            private TridentController _tridentController;

        }        
    }
}