livingcomputermuseum.ContrAlto/Contralto/IO/TridentDrive.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.Logging;
using System;

namespace Contralto.IO
{
    /// <summary>
    /// Encapsulates logic that belongs to a Trident drive, including loading/saving packs,
    /// seeking, and parceling out sector data.
    /// </summary>
    public class TridentDrive
    {
        public TridentDrive(AltoSystem system)
        {
            _system = system;

            _seekEvent = new Event(0, null, SeekCallback);
            Reset();
        }

        public void Reset()
        {
            _sector = 0;
            _cylinder = 0;
            _head = 0;

            _notReady = false;

            UpdateTrackCache();
        }

        public void NewPack(string path, DiskGeometry geometry)
        {
            if (_pack != null)
            {
                UpdateTrackCache();
                _pack.Dispose();
            }

            _pack = FileBackedDiskPack.CreateEmpty(geometry, path);
            Reset();
        }

        public void LoadPack(IDiskPack pack)
        {
            if (_pack != null)
            {
                UpdateTrackCache();
                _pack.Dispose();
            }

            _pack = pack;
            Reset();
        }

        public void UnloadPack()
        {
            if (_pack != null)
            {
                UpdateTrackCache();
                _pack.Dispose();
            }

            _pack = null;
            Reset();
        }

        public bool IsLoaded
        {
            get { return _pack != null; }
        }

        public bool NotReady
        {
            get { return _notReady; }
        }

        public IDiskPack Pack
        {
            get { return _pack; }
        }

        public int Sector
        {
            get { return _sector; }
            set { _sector = value; }
        }       

        public int Head
        {
            get { return _head; }
            set
            {
                if (_head != value)
                {
                    _head = value;
                    UpdateTrackCache();
                }
            }
        }
        
        public int Cylinder
        {
            get { return _cylinder; }
            set
            {
                if (_cylinder != value)
                {
                    _cylinder = value;
                    UpdateTrackCache();
                }
            }
        }

        public bool ReadOnly
        {
            get { return false; }
        }

        public bool Seek(int destCylinder)
        {
            if (destCylinder > _pack.Geometry.Cylinders - 1)
            {
                Log.Write(LogType.Error, LogComponent.TridentController, "Specified cylinder {0} is out of range.  Seek aborted, device check raised.", destCylinder);                
                return false;
            }

            int currentCylinder = _cylinder;
            if (destCylinder != currentCylinder)
            {
                // Do a seek.
                _notReady = true;

                _destCylinder = destCylinder;

                //
                // I can't find a specific formula for seek timing; the Century manual says:
                // "Positioning time for seeking to the next cylinder is normally 6ms, and
                //  for full seeks (814 cylinder differerence) it is 55ms."
                //
                // I'm just going to fudge this for now and assume a linear ramp; this is not
                // accurate but it's not all that important.
                //
                _seekDuration = (ulong)((6.0 + 0.602 * Math.Abs(currentCylinder - destCylinder)) * Conversion.MsecToNsec);

                Log.Write(LogComponent.TridentController, "Commencing seek from {0} to {1}.  Seek time is {2}ns", destCylinder, currentCylinder, _seekDuration);

                _seekEvent.TimestampNsec = _seekDuration;
                _system.Scheduler.Schedule(_seekEvent);
            }
            else
            {
                Log.Write(LogComponent.TridentController, "Seek is a no-op.");
            }

            return true;
        }        

        public ushort ReadHeader(int wordOffset)
        {
            if (wordOffset >= SectorGeometry.Trident.HeaderSize)
            {
                //
                // We just ignore this; the microcode may read extra words
                // and the controller was expected to ignore them.
                //
                Log.Write(LogType.Warning, LogComponent.TridentDisk, "Extra header word read, offset {0}", wordOffset);
                return 0;
            }
            else
            {
                return CurrentSector.ReadHeader(wordOffset);
            }
        }

        public ushort ReadLabel(int wordOffset)
        {
            if (wordOffset >= SectorGeometry.Trident.LabelSize)
            {
                //
                // We just ignore this; the microcode may read extra words
                // and the controller was expected to ignore them.
                //
                Log.Write(LogType.Warning, LogComponent.TridentDisk, "Extra label word read, offset {0}", wordOffset);
                return 0;
            }
            else
            {
                return CurrentSector.ReadLabel(wordOffset);
            }
        }

        public ushort ReadData(int wordOffset)
        {
            if (wordOffset >= SectorGeometry.Trident.DataSize)
            {
                //
                // We just ignore this; the microcode may read extra words
                // and the controller was expected to ignore them.
                //
                Log.Write(LogType.Warning, LogComponent.TridentDisk, "Extra data word read, offset {0 }", wordOffset);
                return 0;
            }
            else
            {
                return CurrentSector.ReadData(wordOffset);
            }
        }

        public void WriteHeader(int wordOffset, ushort word)
        {            
            if (wordOffset >= SectorGeometry.Trident.HeaderSize)
            {
                //
                // We just ignore this; the microcode may send extra words
                // and the controller was expected to ignore them.
                //
                Log.Write(LogType.Warning, LogComponent.TridentDisk, "Extra header word ({0}) written, offset {1}", Conversion.ToOctal(word), wordOffset);
            }
            else
            {
                CurrentSector.WriteHeader(wordOffset, word);
            }
        }

        public void WriteLabel(int wordOffset, ushort word)
        {
            if (wordOffset >= SectorGeometry.Trident.LabelSize)
            {
                //
                // We just ignore this; the microcode may send extra words
                // and the controller was expected to ignore them.
                //
                Log.Write(LogType.Warning, LogComponent.TridentDisk, "Extra label word ({0}) written, offset {1}", Conversion.ToOctal(word), wordOffset);
            }
            else
            {
                CurrentSector.WriteLabel(wordOffset, word);
            }
        }

        public void WriteData(int wordOffset, ushort word)
        {
            if (wordOffset >= SectorGeometry.Trident.DataSize)
            {
                //
                // We just ignore this; the microcode may send extra words
                // and the controller was expected to ignore them.
                //
                Log.Write(LogType.Warning, LogComponent.TridentDisk, "Extra data word ({0}) written, offset {1}", Conversion.ToOctal(word), wordOffset);
            }
            else
            {
                CurrentSector.WriteData(wordOffset, word);
            }
        }

        private void SeekCallback(ulong skewNsec, object context)
        {
            Log.Write(LogComponent.TridentDisk, "Seek to {0} complete.", _destCylinder);

            Cylinder = _destCylinder;
            _notReady = false;
        }

        //
        // Sector management.  We load in an entire track's worth of sectors at a time.
        // When the head or cylinder changes, UpdateTrackCache must be called.
        //
        private void UpdateTrackCache()
        {
            if (_pack != null)
            {
                if (_trackCache == null)
                {
                    //
                    // First time through, initialize the cache.
                    //
                    _trackCache = new DiskSector[_pack.Geometry.Sectors];
                }
                else
                {
                    //
                    // Commit the sectors back to disk before loading in the new ones.
                    //
                    for (int i = 0; i < _trackCache.Length; i++)
                    {
                        _pack.CommitSector(_trackCache[i]);
                    }
                }

                //
                // Load the new sectors for this track.
                //
                for (int i = 0; i < _trackCache.Length; i++)
                {
                    _trackCache[i] = _pack.GetSector(_cylinder, _head, i);
                }
            }
        }

        private DiskSector CurrentSector
        {
            get { return _trackCache[_sector]; }
        }

        private AltoSystem _system;

        //
        // Current disk position
        //
        private int _cylinder;
        private int _head;
        private int _sector;

        // The pack loaded into the drive
        IDiskPack _pack;

        // Drive status
        private bool _notReady;

        // Seek status and control
        private static ulong _seekDuration;
        private Event _seekEvent;
        private int _destCylinder;


        //
        // The track cache
        //
        private DiskSector[] _trackCache;
    }
}