toptensoftware

// Manages allocations within an "address space".
public class RangeAllocator<T>
{
  // Constructor
  public RangeAllocator(int addressSpaceSize);

  // Info accessors
  public int AddressSpaceSize { get; set; }
  public int FreeSpace { get; }
  public int EntryCount { get; }

toptensoftware

// Read a byte from the global heap
public byte ReadByte(ushort seg, ushort offset)
{
    // Crack the selector
    var sel = GetSelector(seg);

    try
    {
        // Read it
        return sel.allocation.buffer[((seg >> 3) - sel.selectorIndex) << 16 | offset];

toptensoftware

// Setup the CPU's instruction pointer
_cpu.cs = selectorFromSegmentIndex(_module.NeHeader.entryPointCS);
_cpu.ip = _module.NeHeader.entryPointIP;

// Run till done
while (!_stopCondition)
{
    _cpu.Step()
}

toptensoftware

public override void RaiseInterrupt(byte interruptNumber)
{
    if (interruptNumber == 0x21 && _cpu.ah == 0x4C)
    {
        _stopCondition = true;
    }
}

toptensoftware

public override void RaiseInterrupt(byte interruptNumber)
{
    switch (interruptNumber)
    {
        case 0x21:
            // DOS Call
            if (_cpu.ah == 0x4C)
                _stopCondition = true;
            break;

toptensoftware

List<Action> _systemThunkHanders = new List<Action>();
public uint CreateSystemThunk(Action handler, ushort popStack)
{
    // Capture address of this thunk
    ushort address = _systemCodeGenPos;

    // Store the handler
    ushort thunkIndex = (ushort)_systemThunkHanders.Count;
    _systemThunkHanders.Add(handler);

toptensoftware

uint _sysRetThunk;
void CreateSysRetThunk()
{
    // Store address
    _sysRetThunk = (uint)(_systemCodeSelector << 16 | _systemCodeGenPos);

    // Get memory buffer
    byte[] mem = _globalHeap.GetBuffer(_systemCodeSelector);

    // INT 81h

toptensoftware

public void CallVM(uint lpfnProc)
{
    // Save the old IP
    var oldCS = cs;
    var oldIP = ip;

    // Setup the new IP
    cs = lpfnProc.Hiword();
    ip = lpfnProc.Loword();

toptensoftware

// Base functionality common to all modules
abstract class ModuleBase
{
}

// Module loaded from 16-bit .exe or .dll
class Module16 : ModuleBase
{
}

toptensoftware

// Locate the module (append ".dll" + look in search path)
var locatedModule = LocateModule(fileOrModuleName, parentPath);
if (locatedModule == null)
    throw new VirtualException(string.Format("Can't find module '{0}'", fileOrModuleName));

// Load it
var nativeModule = new Module16(locatedModule);


// elsewhere....