Working with Microseconds
lazarus / 8-Other

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enko · 2017-08-18 19:13

Im starting to work with Rasperry Pi3 devices and I'm study this C
code :
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i
/********************************    Ultra Sonic Raning module Pin VCC
should*  be connected to 5V
power.******************************/#include <wiringPi.h>#include
<stdio.h>#include <sys/time.h> #define Trig    0#define Echo    1 void
ultraInit(void){        pinMode(Echo, INPUT);        pinMode(Trig,
OUTPUT);} float disMeasure(void){        struct timeval tv1;       
struct timeval tv2;        long time1, time2;    float dis;        
digitalWrite(Trig, LOW);        delayMicroseconds(2);        
digitalWrite(Trig, HIGH);        delayMicroseconds(10);    
 //发出超声波脉冲        digitalWrite(Trig, LOW);                           
                                           while(!(digitalRead(Echo)
== 1));        gettimeofday(&tv1, NULL);           //获取当前时间        
while(!(digitalRead(Echo) == 0));        gettimeofday(&tv2, NULL);   
      //获取当前时间         time1 = tv1.tv_sec * 1000000 + tv1.tv_usec;  
//微秒级的时间        time2  = tv2.tv_sec * 1000000 + tv2.tv_usec;        
dis = (float)(time2 - time1) / 1000000 * 34000 / 2;  //求出距离        
return dis;} int main(void){        float dis;        
if(wiringPiSetup() == -1){ //when initialize wiring failed,print
messageto screen                printf("setup wiringPi failed !");   
           return 1;         }         ultraInit();               
while(1){                dis = disMeasure();               
printf("%0.2f cm\n\n",dis);                delay(300);        }      
 return 0;} 
to interact with gpio i'm using h2wiringpi.pas (digitalWrite,
DigitalRead, delayMicroseconds), to calcolate time difference I'm
using a function found in this forum :
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i function
GetTickCount: Cardinal;var  tv: ptimeval;begin  fpgettimeofday(tv,
nil);  Result := int64(tv.tv_sec) * 1000000 + tv.tv_usec;end; 
when the programm execute GetTickCount I've an Access Violation
Can anyone help me ?

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Thaddy · 2017-08-18 19:24

GetTickCount64 is standard in sysutils... example RPi3 code:
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i uses
sysutils;beginwriteln(GetTickCount64);end.
Your own code contains lots of mistakes, btw:
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i //  use the
above code instead because it faster, monotonic and cross-platform..
but this is your corrected code.function GetTickCount:qword;  // it is
twice the size of a cardinal!! And unsigned!var  tv: ptimeval;begin 
fpgettimeofday(tv, nil); // sure about nil?......?? Also wrong anyway
fpgettimeofday returns microsecond resolution NOT nanoseconds. This is
also the acces violation...   Result := tv.tv_sec * 1000000 +
tv.tv_usec; // is enough. You cast to a signed int64 and return a 32
bit type cardinal.... Won't overflow for a couple of million yearsend;

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enko · 2017-08-19 10:38

Thanks Thaddy for your answer

Using your function GetTickCount revisited I continue to have Access
Violation.

I copy and paste your function GetTickCount revisited in a new console
program
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i program
Project1;uses SysUtils, Unix, baseunix; function GetTickCount:qword;
 // it is twice the size of a cardinal!! And unsigned!var  tv:
PTimeVal;  tz: PTimeZone;begin  tz := nil;  fpgettimeofday(tv, tz); //
sure about nil?......?? Also wrong anyway fpgettimeofday returns
microsecond resolution NOT nanoseconds. This is also the acces
violation...  Result := tv.tv_sec * 1000000 + tv.tv_usec; // is
enough. You cast to a signed int64 and return a 32 bit type
cardinal.... Won't overflow for a couple of million yearsend; begin 
writeln(GetTickCount);end.     
I have some error and warning on compiling

project1.lpr(10,20) Warning: Local variable "tv" does not seem to be
initialized
project1.lpr(11,16) Error: Illegal qualifier
project1.lpr(11,16) Hint: may be pointer dereference is missing
project1.lpr(11,15) Error: Incompatible types: got "ptimeval" expected
"QWord"
project1.lpr(11,16) Fatal: Syntax error, ";" expected but "identifier
TV_SEC" found

googling "free pascal  fpgettimeofday" ALL examples / code are passing
to the fpgettimeofday function the PTimeZone = nil

Note i'm using lazarus version installed on a Raspberry Pi3

Have you any precious suggestion ?
Thanks

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enko · 2017-08-19 10:44

Also
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i uses
sysutils;beginwriteln(GetTickCount64);end. 
On compiling I have Error: Identifier not found "GetTickCount64"

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Thaddy · 2017-08-19 11:12

Quote from: enko on August 19, 2017, 12:44:18 pmAlso
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i uses
sysutils;beginwriteln(GetTickCount64);end. 
On compiling I have Error: Identifier not found "GetTickCount64"

That's very very strange because I wrote the example (and this reply!)
from a Raspberry Pi 3. Are you sure you are not using an old version?
Did you upgrade to Stretch already? (That has FPC 3.0.0)..
That should not be necessary, but at least 3 is still a supported
version:
Code: [Select]pi@raspberrypi:~/fpcdemos $ fpc -CX -XXs counter.pas
Free Pascal Compiler version 3.1.1-r36940 [2017/08/18] for arm
Copyright (c) 1993-2017 by Florian Klaempfl and others
Target OS: Linux for ARMHF
Compiling counter.pas
Linking counter
7 lines compiled, 0.9 sec
pi@raspberrypi:~/fpcdemos $ ./counter
20724027

Anyway, your homebrew gettickkount is wrong, I am not going to debug
that any further.

The standard implementation in sysutils looks like this:
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i function
GetTickCount64: QWord;var  tp: TTimeVal;  {$IFDEF HAVECLOCKGETTIME} 
ts: TTimeSpec;  {$ENDIF}  begin {$IFDEF HAVECLOCKGETTIME}   if
clock_gettime(CLOCK_MONOTONIC, @ts)=0 then     begin     Result :=
(Int64(ts.tv_sec) * 1000) + (ts.tv_nsec div 1000000);     exit;   
 end; {$ENDIF}  fpgettimeofday(@tp, nil);  Result := (Int64(tp.tv_sec)
* 1000) + (tp.tv_usec div 1000);  // look here!end;
Since RPi does have HAVECLOCKGETTIME that is the version that gets
executed.

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enko · 2017-08-19 11:35

It seems I have an old version ...

pi@raspberrypi:~ $ fpc
Free Pascal Compiler version 2.6.4+dfsg-4+rpi1 [2014/10/21] for arm

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Eugene Loza · 2017-08-19 11:48

You may do it this way (don't mix records with pointers to records):
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i function
GetTickCount: Int64;var  tv: TTimeval;begin  FpGettimeofday(@tv,
nil);  Result := Int64(tv.tv_sec) * 1000000 + Int64(tv.tv_usec);end;
or
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i function
GetTickCount: Int64;var  tv: PTimeval;begin  FpGettimeofday(tv, nil); 
Result := Int64(tv^.tv_sec) * 1000000 + Int64(tv^.tv_usec);end;
Similar code works fine for me.

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enko · 2017-08-19 12:08

Thaddy
can you tell me what I must to do to upgrade FPC e Lazarus IDE to
lastest release for RaspBerry ??
Thanks a lot for your patience.

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Thaddy · 2017-08-19 14:03

See Raspberry.org
The new Raspbian Stretch comes with fpc 3.0.0 and Lazarus 1.6.2
From fpc 3.0 it is easy to build a new Lazarus from source and also a
new FPC 3.0.4.

So first advice is to update to latest RaspBian stretch.
Then sudo apt-get purge fpc && apt-get  autoremove && sudo apt-get
install fpc

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Thaddy · 2017-08-19 14:09

Quote from: Eugene Loza on August 19, 2017, 01:48:31 pmYou may do it
this way (don't mix records with pointers to records):
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i function
GetTickCount: Int64;var  tv: TTimeval;begin  FpGettimeofday(@tv,
nil);  Result := Int64(tv.tv_sec) * 1000000 + Int64(tv.tv_usec);end;
or
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i function
GetTickCount: Int64;var  tv: PTimeval;begin  FpGettimeofday(tv, nil); 
Result := Int64(tv^.tv_sec) * 1000000 + Int64(tv^.tv_usec);end;
Similar code works fine for me.

Both are wrong. I already gave the correct calculation from the
official sources (sysutils).
Yours are prone to range checks and overflow.! You should use the
version from sysutils.
Code: [Select]// for if there is no CLOCK*
  fpgettimeofday(@tp, nil);
  Result := (Int64(tp.tv_sec) * 1000) + (tp.tv_usec div 1000);  //
look here!