[Lazarus] Portable way to get accurate timestamps?

[Michael Van Canneyt]

On Tue, 22 Feb 2011, Bo Berglund wrote:

> On Tue, 22 Feb 2011 08:50:33 +0100 (CET), Michael Van Canneyt
> <michael at freepascal.org> wrote:
>
>>> I should have added that instead of a sawtooth like noise component
>>> using Frac(Now()) * 24*3600 to get the second since midnight gives
>>> random noise in the seconds values of about 3-4 ms.
>>> Another observation is that there seems to be no data smaller than ms.
>>> If I format this value as a float with more decimals than 3 I always
>>> only see zeroes.
>>
>> That is logical, since TDateTime only is accurate to millisecond precision.
>>
>
> Granted that, but right now I am mostly interested in finding a way to
> time an external event source such that I can measure the time between
> events.
>
> After googling a bit I have come up with the following, which is a
> variation of a delay function that I created years ago in Delphi to
> enable me to output pulses that are timed to milliseconds.
> The delay is now converted to a time retrieval function:
>
> function TForm1.GetMillisecondTime: Int64;
> var
>  Freq,
>  Ts: Int64;
> begin
>  QueryPerformanceCounter(Ts);
>  QueryPerformanceFrequency(Freq);
>  if (Ts = 0) or (Freq = 0) then exit;
>  Freq := Freq div 1000;
>  Result := TS div Freq;
> end;
>
> When I try this in Lazarus I get an "Identifier not found" error (not
> surprising).
> What should I do in order to get this to compile?
> Any suitable unit to add to the uses clause?

If you are on windows: add the windows unit.

If you are on another platform: these functions simply do not exist on other platforms.

Michael.