[Lazarus] Where is hwiringPi?

Dennis dec12 at avidsoft.com.hk
Sat Sep 19 06:55:00 CEST 2015

I have written a small program using FPC to run on Rasp Pi to connect, 
via i2c, to a temperature/humidity sensor and save the readings into a 
MySQL database.
Initially, I tried to use wiringPi, but I later found out it was very 
simple to directly connect to i2c via fpRead() . It was as simple as:

   I2C_SLAVE = 1795;
   CMD_SOFT_RESET : byte = $FE;
   CMD_READ_TEMP_NOHOLD : byte = $F3;
   CMD_READ_HUM_NOHOLD : Byte =  $F5;

var TheDeviceNo : integer = $40;
     ThePath : String = '/dev/i2c-1';
     DeviceHandle : integer;

    DeviceHandle := fpopen(ThePath,O_RDWR); //Open the I2C bus in 
Read/Write mode
    iio:= FpIOCtl(DeviceHandle, I2C_SLAVE, pointer(TheDeviceNo)); //Set 

    If (iio <> 0) or (DeviceHandle < 0) Then begin
       DeviceHandle := 0;
       raise Exception.Create('Failed to open '+ThePath+' device# 

//to read a floating variable:
function ReadFloat(const TheRegNo: byte; TheOffset,  TheSlope: double): 
var aBytes : array[0..3] of byte;
   i : integer;
  fpwrite(DeviceHandle, TheRegNo, 1);
  Sleep(100); //for safety only. not sure if needed

  Fillchar(aBytes, sizeof(aBytes), 0);
  fpread(DeviceHandle, aBytes, 3);

//the following is only specific to the themometer which requires some 
conversion in the data read.
  if IsCRC8Ok(aBytes) then begin
    result := ((aBytes[0] shl 8) or aBytes[1] ) and ($FFFC);
    result  :=result/65536;
    result := result * TheSlope + TheOffset;
  end else
    raise ECRCError.Create('');

//to reset the themometer
   fpwrite(DeviceHandle, CMD_SOFT_RESET, 1);

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