[Lazarus] Portable way to get accurate timestamps?

[Bo Berglund]

On Mon, 21 Feb 2011 07:23:54 +0100, Bo Berglund
<bo.berglund at gmail.com> wrote:

>When I run a test against a fairly accurate GPS time source I see that
>there is an uncertainty of about 16 ms in the time given such that if
>GetTickCount is executed at exactly 1 second intervals the last two
>digits of the value is not the same as it should be.
>Instead it slowly (over a period of 16 seconds) reduces by 16 ms and
>then suddenly restores to a max value.
>It is like a superimposed sawtooth with an amplitude of 16 ms.
>
>The posted variation is apparently a Linux platform compatible version
>that returns a millisecond value the same way as the Windows version
>does, since there is no Windows GetTickCount API call in Linux.
>
>I used this also on Windows in my tests and then the value does not
>exhibit the sawtooth anymore. So I assume that Now() gets its time
>from another source than the timer counter driving GetTickCount and
>this is more accurate.

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.


-- 
Bo Berglund
Developer in Sweden