How to create a high resolution timer

Problem/Question/Abstract:

How to create a high resolution timer

Answer:

Windows is not a real time operating system so it is not really able to reliably achieve high accuracy timing without using a device driver. The best I have been able to get is a few nanoseconds using QueryPerformanceCounter. This is the procedure I use:

var
  WaitCal: Int64;

procedure Wait(ns: Integer);
var
  Counter, Freq, WaitUntil: Int64;
begin
  if QueryPerformanceCounter(Counter) then
  begin
    QueryPerformanceFrequency(Freq);
    WaitUntil := Counter + WaitCal + (ns * (Freq div 1000000));
    while Counter < WaitUntil do
      QueryPerformanceCounter(Counter);
  end
  else
    Sleep(ns div 1000);
end;

To get improved accuracy do this a little while before using Wait()

var
  Start, Finish: Int64;

Application.ProcessMessages;
Sleep(10);
QueryPerformanceCounter(Start);
Wait(0);
QueryPerformanceCounter(Finish);
WaitCal := Start - Finish;

A trick I have found to increase the reliability of this on my computer is to call Wait like this:

Application.ProcessMessages;
Sleep(0);
DoSomething;
Wait(10);
DoSomethingElse;