[fpc-other] [fpc-pascal] Access GPIO pins on RPi2 without root?

[Bo Berglund]

>If it would be a FPC specific usage question then it would be a bad idea to
post it to fpc-other.
>However as others have already stated accessing GPIOs on RPi is non
specific to FPC and thus it doesn't need to be on fpc-pascal or even
fpc-devel.

OK, I understand.
I have researched a bit more now given the input I received.
Apparently on a Raspberry Pi there are several defined user groups with
specific permissions on the /dev/xxx device files.
It seems like the user pi is member of a lot of these groups and thus would
not really need root to run a program accessing the hardware.
However, when I look at the unit pigpio.pas I found in the lazarus wiki
following a link in one of the responses I got I see this:

function TIoDriver.MapIo: boolean;
begin
 Result := True;
 fd := fpopen('/dev/mem', O_RdWr or O_Sync); // Open the master /dev/memory
device
  if fd < 0 then
  begin
    Result := False; // unsuccessful memory mapping
  end;
 //
end;

Notice that the file used is /dev/mem

I don't know if there exists a user group named mem, but in any case the
user pi is not member of any such group.
Could this be the cause for root to be required?

pi at rpi2-jessie ~ $ groups pi
pi : pi adm dialout cdrom sudo audio video plugdev games users input netdev
spi i2c gpio

I asked a similar question in the Raspberry Pi forum and got a reply telling
me to modify this to become:

fd := fpopen('/dev/gpiomem', O_RdWr or O_Sync);

While writing this the final compile of lazarus just finished (I have
started from scratch using Raspbian Jessie and installed trunk of both fpc
and lazarus from svn).
So now I will soon be able to check this....

Best Regards, 

Bo Berglund