[fpc-pascal] Microsecond Delay Suggestions?

[Dmitry Boyarintsev]

On Tue, Jul 26, 2016 at 12:38 PM, James Richters <
james at productionautomation.net> wrote:

> What I need is a timer that I can specify in microseconds, a millisecond
> is too long.   I am using it for timing to read in a string on a serial
> connection.  My fastest baudrate is 250000, so at that rate I would need to
> delay only 36 microseconds.  So I can’t use sleep () or delay () because
> they only go down to 1mS and that’s too slow.
>

Here's an example of Sleep with microseconds that I came up with

procedure SleepMcs(mcs: Int64);
var
  ct : TLargeInteger;
  fr : TLargeInteger;
  af  : TLargeInteger;
  trg : TLargeInteger;
const
  NanoInMicro = 1000;
begin
  QueryPerformanceCounter(ct);
  QueryPerformanceFrequency(fr);
  trg:=round(mcs * NanoInMicro / (NSInSec/fr));
  repeat
    QueryPerformanceCounter(af);
  until trg<=(af-ct);
end;

I'm hoping that there's a better solution out there, because this procedure
will end up with 100% CPU load.
I doubt it's possible to unload the CPU, since the windows scheduler is in
milliseconds accuracy.
May be a lower (kernel/driver) level allows that.

thanks,
Dmitry
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