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

[Bo Berglund]

OK,
I have now subscribed to the fpc-other list.
Hopefully I can ask "stupid" fpc usage questuions there... 


Best Regards, 

Bo Berglund 

-Original Message-
You just mentioned that you don't like to subscribe to mailing lists 
because you already receive many mails. By posting mails on a list that 
are not really on topic, you make that exact same problem worse for 
other people that do prefer to use email rather than use a web or nntp 
interface.


Jonas

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Re: [fpc-pascal] Access GPIO pins on RPi2 without root? [lenghty and very [OT] ]

[Lukasz Sokol]

On 09/10/15 08:50, Bo Berglund wrote:
> On Thu, 08 Oct 2015 22:01:49 +, Mark Morgan Lloyd
>  wrote:
>>> Sorry for causing a problem here...
>>> The lists you refer to are not present in the Gmane newsserver as a
>>> newsgroup so I cannot access it.
>>
>> I suggest setting up a direct subscription using the instructions given 
>> at http://www.freepascal.org/maillist.var  Things like Gmane are really 
>> only useful as long-term archives.
> 
> Well, I don't like to have my inbox receive the number of emails on a
> list like this. The new interface is a much better way in my view.
> I already receive 100+ emails every day so doubling this seems not to
> be a good way for me
> 
I second that,
especially thread.gmane.org is nice - also one can use the mail to news gateway,
through any news/reader/mua (like I use thunderbird).

Bo, how about if we petition the gmane admins to subscribe to fpc-other?
There is a lot of discussion that seems to be going on there. 
 If you write one like that, you've got my vote too.

(and sorry to the list admins, for bringing it on this list/topic, 
gmane tries to obfuscate senders emails when using the mail-to-news gateway)

>>> I will try to locate an updated pigpio.pas file by asking in the
>>> Lazarus forum instead.
>>
>> I would strongly suggest going through /sys/class/gpio first, since you 
>> can exercise it using  echo  and there are fewer things to get wrong.
> 
> I have seen you mention "echo" a number of times and I have gone back
> (in the Gmane gmane.comp.compilers.free-pascal.general news archive in
> my newsreader) to locate the exact method for this but I failed.

(again sorry to the admins here that this may be lengthy and ot, but Bo's email 
has been garbled by Gmane)

'echo' is a distribution-contained (usually a separate program, but that 
depends on the distribution)
that writes its given parameters to std-output, as text, then the '>' redirects 
it to a file.

Long story short, most you need to remember, in unix-like systems everything 
that can be, is treated as a file,
placed under the single virtual file system (VFS) hierarchy. No 'drive 
letters', etc.

When you issue a command 'echo something > /path/to/file' there are several 
things that may happen;
The '>' operation tells the shell to take the echo's std-output and write it to 
the file.
  (OT: if you used >> instead, it would have been added/appended to file; only 
really works on disk for this reason)

In higher-level compiled languages like c or pascal you achieve this by
opening the file, writing to it (possibly preceded by doing a 'rewrite' it, but 
not sure) and then closing.
(remember that either of these 3 operations may throw an error which you need 
to handle)

in case of GPIO, the in-kernel driver has VFS hooks that tell it :
 - someone has 'just' replaced the content of the file
in its virtual filesystem hierarchy under /sys/class/gpio/* with 'something', 
so it intercepts that write, interprets/sanitizes what it has been given, 
and handles the userspace programs writing to that file.

It also detects 'reads' from the file similarly, 
some drivers support just reading from a file in a loop, 
by means of likes of: 'open-repeat-read-sleep-untilneeded-close';
but some may need an 'repeat-open-read-close-sleep-untilneeded' pattern; 

there is also a family of *notify system functions/calls, 
but that seems to not be as loved by the system/kernel developers as the 
simpl(istic) open-read-close chain.

It really can't be done any simpler to the userspace, at least in 
Unix-like/Linux world.
it also has interesting implications (regarding permissions)
that this space is really too small and off-topic to contain.

> And I am a total noob in this low level handling of Linux...
> I will continue searching for your echo examples after I return home
> again.
> 

It's not as low-level as kernel, so don't worry ;) 
and yes the information is all over the place and incredibly scattered.
But that's the 'feature' with all the FOSS stuff, it's a myriad of independent 
projects.

el es

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

[Marc Santhoff]

On Fr, 2015-10-09 at 09:50 +0200, Bo Berglund wrote:
> On Thu, 08 Oct 2015 22:01:49 +, Mark Morgan Lloyd
>  wrote:

> >> I will try to locate an updated pigpio.pas file by asking in the
> >> Lazarus forum instead.
> >
> >I would strongly suggest going through /sys/class/gpio first, since you 
> >can exercise it using  echo  and there are fewer things to get wrong.
> 
> I have seen you mention "echo" a number of times and I have gone back
> (in the Gmane gmane.comp.compilers.free-pascal.general news archive in
> my newsreader) to locate the exact method for this but I failed.
> And I am a total noob in this low level handling of Linux...
> I will continue searching for your echo examples after I return home
> again.

A starting point for understanding and finding additional information
about udev is there:

https://en.wikipedia.org/wiki/Udev

Another issue of interest would be basic user management. I suggest
going to the documentation pages of the distro you use and reading some
basic administration docs.

Short pre-info:

Each user on your RPi can be member of multiple groups. This is managed
in the file /etc/group.

Group membership is for giving rights regarding software and hardware
access to users. E.g. by making a user a member of the group
"dialer" (or similar) this user is allowed to use modems attached to the
computer. Each file and directory has an owner and a set of flags for
managing access allowance. Try "man chown" and "man chmod" on the pi's
console window. And since hardware devices are made usable via device
nodes, which are files in the /dev hierarchie, anything is a file in
Linux/Unix and this rights management work for anything.

To map hardware access rights to groups, udev is used. Udev is
instructed to do this by rules. I assume RPi has those udev rules built
in, because the special gpio hardware has to be managed somehow.

-- 
Marc Santhoff 

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

[Mark Morgan Lloyd]

Jonas Maebe wrote:

Bo Berglund wrote:

I have asked about this on the Pi forum instead, but I fear noone
(almost) over there use free-pascal so I have no high hopes.


The point is that this question is completely unrelated to Pascal or 
Free Pascal. It's a basic Unix/Linux usage question, which is 
independent of the used programming language. If you ask how to access 
"GPIO pins on RPi2 without root" on a Linux/Raspberry forum, any answer 
you will get will equally apply to FPC as to any other language. You 
already have the Pascal code to access the pins from the wiki, per a 
previous post of yours, so you don't have to mention FPC/Pascal at all.


You just mentioned that you don't like to subscribe to mailing lists 
because you already receive many mails. By posting mails on a list that 
are not really on topic, you make that exact same problem worse for 
other people that do prefer to use email rather than use a web or nntp 
interface.


FWIW, I agree and I'd like to apologise for making things slightly 
worse. However I was doing my best to help somebody who obviously still 
had problems, even though I anticipated that he'd eventually put himself 
in the position where I had no choice but to stop.


--
Mark Morgan Lloyd
markMLl .AT. telemetry.co .DOT. uk

[Opinions above are the author's, not those of his employers or colleagues]
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Re: [fpc-pascal] Access GPIO pins on RPi2 without root?

[Lukasz Sokol]

On 09/10/15 09:33, Jonas Maebe wrote:
> Bo Berglund wrote:
>> I have asked about this on the Pi forum instead, but I fear noone 
>> (almost) over there use free-pascal so I have no high hopes.
> 
> The point is that this question is completely unrelated to Pascal or
> Free Pascal. It's a basic Unix/Linux usage question, which is
> independent of the used programming language. If you ask how to
> access "GPIO pins on RPi2 without root" on a Linux/Raspberry forum,
> any answer you will get will equally apply to FPC as to any other
> language. You already have the Pascal code to access the pins from
> the wiki, per a previous post of yours, so you don't have to mention
> FPC/Pascal at all.
> 
> You just mentioned that you don't like to subscribe to mailing lists
> because you already receive many mails. By posting mails on a list
> that are not really on topic, you make that exact same problem worse
> for other people that do prefer to use email rather than use a web or
> nntp interface.
> 

Hi Jonas,

would you support us, writing to Gmane to actually subscribe to
fpc-other mailing list ? 

Gmane is nice not just for storage, I just more like separation of traffic
between my emails and the actual discussions; like in the olden days...
and I'm sorry but forums don't really cut it for me, for various reasons.

el es

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

[Jonas Maebe]

Bo Berglund wrote:

I have asked about this on the Pi forum instead, but I fear noone
(almost) over there use free-pascal so I have no high hopes.


The point is that this question is completely unrelated to Pascal or 
Free Pascal. It's a basic Unix/Linux usage question, which is 
independent of the used programming language. If you ask how to access 
"GPIO pins on RPi2 without root" on a Linux/Raspberry forum, any answer 
you will get will equally apply to FPC as to any other language. You 
already have the Pascal code to access the pins from the wiki, per a 
previous post of yours, so you don't have to mention FPC/Pascal at all.


You just mentioned that you don't like to subscribe to mailing lists 
because you already receive many mails. By posting mails on a list that 
are not really on topic, you make that exact same problem worse for 
other people that do prefer to use email rather than use a web or nntp 
interface.



Jonas
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Re: [fpc-pascal] Access GPIO pins on RPi2 without root?

[Bo Berglund]

On Thu, 08 Oct 2015 22:01:49 +, Mark Morgan Lloyd
 wrote:
>> Sorry for causing a problem here...
>> The lists you refer to are not present in the Gmane newsserver as a
>> newsgroup so I cannot access it.
>
>I suggest setting up a direct subscription using the instructions given 
>at http://www.freepascal.org/maillist.var  Things like Gmane are really 
>only useful as long-term archives.

Well, I don't like to have my inbox receive the number of emails on a
list like this. The new interface is a much better way in my view.
I already receive 100+ emails every day so doubling this seems not to
be a good way for me

>> I will try to locate an updated pigpio.pas file by asking in the
>> Lazarus forum instead.
>
>I would strongly suggest going through /sys/class/gpio first, since you 
>can exercise it using  echo  and there are fewer things to get wrong.

I have seen you mention "echo" a number of times and I have gone back
(in the Gmane gmane.comp.compilers.free-pascal.general news archive in
my newsreader) to locate the exact method for this but I failed.
And I am a total noob in this low level handling of Linux...
I will continue searching for your echo examples after I return home
again.

-- 
Bo Berglund
Developer in Sweden

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

[Henry Vermaak]

On Wed, Oct 07, 2015 at 01:09:58PM +0200, Bo Berglund wrote:
> On Wed, 07 Oct 2015 10:05:03 +0200, Jonas Maebe
>  wrote:
> >Bo Berglund wrote on Wed, 07 Oct 2015:
> >
> >> How can one control the GPIO outputs on a Raspberry Pi2 without
> >> needing the program to run as root? I am using Raspbian Wheezy and I
> >> need to add two relays controls to my program.
> >
> >This really has nothing to do with either FPC or Pascal programming in  
> >general. Please ask such questions on the fpc-other list in the future.
> >
> I think that it really does because there must be some interface
> between the FPC system and the underlying operating system managing
> the hardware.

You access the GPIOs via the kernel's sysfs interface.  The files are
all under /sys/class/gpio.  I'd be pretty amazed if your distro doesn't
already have a udev rule to set a certain group for those files.  You
probably just have to add your user to that group.

Henry
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Re: [fpc-pascal] Access GPIO pins on RPi2 without root?

[Mark Morgan Lloyd]

Henry Vermaak wrote:

On Wed, Oct 07, 2015 at 01:09:58PM +0200, Bo Berglund wrote:

On Wed, 07 Oct 2015 10:05:03 +0200, Jonas Maebe
 wrote:

Bo Berglund wrote on Wed, 07 Oct 2015:


How can one control the GPIO outputs on a Raspberry Pi2 without
needing the program to run as root? I am using Raspbian Wheezy and I
need to add two relays controls to my program.
This really has nothing to do with either FPC or Pascal programming in  
general. Please ask such questions on the fpc-other list in the future.



I think that it really does because there must be some interface
between the FPC system and the underlying operating system managing
the hardware.


You access the GPIOs via the kernel's sysfs interface.  The files are
all under /sys/class/gpio.  I'd be pretty amazed if your distro doesn't
already have a udev rule to set a certain group for those files.  You
probably just have to add your user to that group.


Yes, it's the gpio group. I worked through the first couple of steps as 
described on the Lazarus wiki page manually (i.e. using echo from the 
command line), so can confirm that it's broadly accurate as of Raspbian 
"Wheezy".


--
Mark Morgan Lloyd
markMLl .AT. telemetry.co .DOT. uk

[Opinions above are the author's, not those of his employers or colleagues]
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Re: [fpc-pascal] Access GPIO pins on RPi2 without root?

[Bo Berglund]

On Thu, 08 Oct 2015 13:15:10 +, Mark Morgan Lloyd
 wrote:

>> You access the GPIOs via the kernel's sysfs interface.  The files are
>> all under /sys/class/gpio.  I'd be pretty amazed if your distro doesn't
>> already have a udev rule to set a certain group for those files.  You
>> probably just have to add your user to that group.
>
>Yes, it's the gpio group. I worked through the first couple of steps as 
>described on the Lazarus wiki page manually (i.e. using echo from the 
>command line), so can confirm that it's broadly accurate as of Raspbian 
>"Wheezy".
Did you mean this page:
http://wiki.freepascal.org/Lazarus_on_Raspberry_Pi#5._PiGpio_Low-level_native_pascal_unit_.28GPIO_control_instead_of_wiringPi_c_library.29

It contains a unit PiGpio for the Broadcom chip on the original Pi.
Is this some the fpc wrapper that handles what has been described in
this thread so an fpc program can actually read and write the GPIO
pins?

It seems easy enough to use were it not for the discussion here
talking about modifying user permissions on Linux to make the program
run...

This is what I see in the gpio dir:
root@rpi2b-wheezy:/sys/class/gpio# ls -la
total 0
drwxrwx---  2 root gpio0 Jan  1  1970 .
drwxr-xr-x 44 root root0 Oct  8 20:38 ..
-rwxrwx---  1 root gpio 4096 Jan  1  1970 export
lrwxrwxrwx  1 root gpio0 Jan  1  1970 gpiochip0 ->
../../devices/soc/3f20.gpio/gpio/gpiochip0
-rwxrwx---  1 root gpio 4096 Jan  1  1970 unexport


-- 
Bo Berglund
Developer in Sweden

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

[Mark Morgan Lloyd]

Bo Berglund wrote:

On Thu, 08 Oct 2015 19:48:54 +, Mark Morgan Lloyd
 wrote:

Do not, under any circumstances, try to fiddle with the permission of 
those files/directories. Instead, add the gpio group to your normal user 
(as I have already said).


Jonas has already asked us to discuss this elsewhere, i.e. either the 
fpc-other or lazarus-other mailing list, and I really do not want to 
upset the list managers by going into basic unix management or into 
things which are specific to managing the RPi.


Having said that, by analogy if you want to drive one of the serial 
ports on a Linux system you usually end up adding the dialout group to 
your normal user ID. If you aren't prepared to discuss this in one of 
the more general MLs, then I suggest researching that and then extending 
what you learn to adding the gpio group to your normal user.


Sorry for causing a problem here...
The lists you refer to are not present in the Gmane newsserver as a
newsgroup so I cannot access it.


I suggest setting up a direct subscription using the instructions given 
at http://www.freepascal.org/maillist.var  Things like Gmane are really 
only useful as long-term archives.



I have asked about this on the Pi forum instead, but I fear noone
(almost) over there use free-pascal so I have no high hopes.

The user pi seems to be in the required group so I take it there is no
need to sudo any execution of the program for user pi?
pi@rpi2b-wheezy ~ $ groups pi
pi : pi adm dialout cdrom sudo audio video plugdev games users netdev
input spi i2c gpio


Or add the gpio group to your normal userid. However the "right" way of 
doing this usually relies on a system-specific user management program 
(the "wrong" way, which most people use in practice, is to edit 
/etc/group and /etc/gshadow).



I will try to locate an updated pigpio.pas file by asking in the
Lazarus forum instead.


I would strongly suggest going through /sys/class/gpio first, since you 
can exercise it using  echo  and there are fewer things to get wrong.


--
Mark Morgan Lloyd
markMLl .AT. telemetry.co .DOT. uk

[Opinions above are the author's, not those of his employers or colleagues]
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Re: [fpc-pascal] Access GPIO pins on RPi2 without root?

[Bo Berglund]

On Thu, 08 Oct 2015 19:48:54 +, Mark Morgan Lloyd
 wrote:

>Do not, under any circumstances, try to fiddle with the permission of 
>those files/directories. Instead, add the gpio group to your normal user 
>(as I have already said).
>
>Jonas has already asked us to discuss this elsewhere, i.e. either the 
>fpc-other or lazarus-other mailing list, and I really do not want to 
>upset the list managers by going into basic unix management or into 
>things which are specific to managing the RPi.
>
>Having said that, by analogy if you want to drive one of the serial 
>ports on a Linux system you usually end up adding the dialout group to 
>your normal user ID. If you aren't prepared to discuss this in one of 
>the more general MLs, then I suggest researching that and then extending 
>what you learn to adding the gpio group to your normal user.

Sorry for causing a problem here...
The lists you refer to are not present in the Gmane newsserver as a
newsgroup so I cannot access it.
I have asked about this on the Pi forum instead, but I fear noone
(almost) over there use free-pascal so I have no high hopes.

The user pi seems to be in the required group so I take it there is no
need to sudo any execution of the program for user pi?
pi@rpi2b-wheezy ~ $ groups pi
pi : pi adm dialout cdrom sudo audio video plugdev games users netdev
input spi i2c gpio

I will try to locate an updated pigpio.pas file by asking in the
Lazarus forum instead.
Bye!

-- 
Bo Berglund
Developer in Sweden

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

[Mark Morgan Lloyd]

Bo Berglund wrote:

On Thu, 08 Oct 2015 13:15:10 +, Mark Morgan Lloyd
 wrote:


You access the GPIOs via the kernel's sysfs interface.  The files are
all under /sys/class/gpio.  I'd be pretty amazed if your distro doesn't
already have a udev rule to set a certain group for those files.  You
probably just have to add your user to that group.


Yes, it's the gpio group. I worked through the first couple of steps as 
described on the Lazarus wiki page manually (i.e. using echo from the 
command line), so can confirm that it's broadly accurate as of Raspbian 
"Wheezy".

Did you mean this page:
http://wiki.freepascal.org/Lazarus_on_Raspberry_Pi#5._PiGpio_Low-level_native_pascal_unit_.28GPIO_control_instead_of_wiringPi_c_library.29

It contains a unit PiGpio for the Broadcom chip on the original Pi.
Is this some the fpc wrapper that handles what has been described in
this thread so an fpc program can actually read and write the GPIO
pins?

It seems easy enough to use were it not for the discussion here
talking about modifying user permissions on Linux to make the program
run...

This is what I see in the gpio dir:
root@rpi2b-wheezy:/sys/class/gpio# ls -la
total 0
drwxrwx---  2 root gpio0 Jan  1  1970 .
drwxr-xr-x 44 root root0 Oct  8 20:38 ..
-rwxrwx---  1 root gpio 4096 Jan  1  1970 export
lrwxrwxrwx  1 root gpio0 Jan  1  1970 gpiochip0 ->
./../devices/soc/3f20.gpio/gpio/gpiochip0
-rwxrwx---  1 root gpio 4096 Jan  1  1970 unexport


Do not, under any circumstances, try to fiddle with the permission of 
those files/directories. Instead, add the gpio group to your normal user 
(as I have already said).


Jonas has already asked us to discuss this elsewhere, i.e. either the 
fpc-other or lazarus-other mailing list, and I really do not want to 
upset the list managers by going into basic unix management or into 
things which are specific to managing the RPi.


Having said that, by analogy if you want to drive one of the serial 
ports on a Linux system you usually end up adding the dialout group to 
your normal user ID. If you aren't prepared to discuss this in one of 
the more general MLs, then I suggest researching that and then extending 
what you learn to adding the gpio group to your normal user.


--
Mark Morgan Lloyd
markMLl .AT. telemetry.co .DOT. uk

[Opinions above are the author's, not those of his employers or colleagues]
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Re: [fpc-pascal] Access GPIO pins on RPi2 without root?

[leledumbo]

>How can one control the GPIO outputs on a Raspberry Pi2 without needing the
program to run as root?

sudo chown root 
sudo chmod 4755 

The 4 is setuid bit, which will allow normal users to run the program but
the program itself has root privilege.



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

[Lukasz Sokol]

On 07/10/15 08:02, Bo Berglund wrote:
> How can one control the GPIO outputs on a Raspberry Pi2 without
> needing the program to run as root? I am using Raspbian Wheezy and I
> need to add two relays controls to my program.
> The pages I have found with google are for the original Pi so the
> connector referenced is the wrong size and it is also always mentioned
> that the program must be run as root.
> My program must be started every minute by cron so I don't know how
> this will happen...
> (Not so used to Linux)
> 
> Do I need to install some driver in Raspbian to allow access to the
> GPIO ports from FPC?
> 
> 

Apart from running SUID Root, which is generally discouraged (there is lots of 
answers on why setuid root is bad)

I'd probably search for some udev rules to make up - to chown the gpio
devices in /dev to root:gpio, (for example) and your unprivileged user to
be a member of group gpio;

( possibly https://www.raspberrypi.org/forums/viewtopic.php?f=29=9667, but
also worth checking out other 
https://www.google.com/search?q=raspberry+pi+udev+gpio+user=utf-8=utf-8 
results.)

el es

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

[Jonas Maebe]

Bo Berglund wrote on Wed, 07 Oct 2015:


How can one control the GPIO outputs on a Raspberry Pi2 without
needing the program to run as root? I am using Raspbian Wheezy and I
need to add two relays controls to my program.


This really has nothing to do with either FPC or Pascal programming in  
general. Please ask such questions on the fpc-other list in the future.


Thanks,


Jonas
FPC mailing lists admin

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

[Michael Van Canneyt]

On Wed, 7 Oct 2015, Mark Morgan Lloyd wrote:


Jonas Maebe wrote:

Bo Berglund wrote on Wed, 07 Oct 2015:


I think that it really does because there must be some interface
between the FPC system and the underlying operating system managing
the hardware.


On Linux/Unix, every interface to hardware gets exposed as a file 
(generally under /dev). Sometimes you have libraries that provide a higher 
level interface, but in the end it will always access that file. If you 
need root permissions to perform actions on this file with language X, you 
will also need them with language Y and also if you use library Z to access 
it. The file operations are basic POSIX operations (open, read, write, 
ioctl, close), which are available with an "fp" prefix via the baseunix and 
unix units, and which are the same in C or other languages.


If you have a library that you want to use, then you can of course ask here 
whether anyone has translated the headers for it (which will probably be in 
C) to Pascal or so.


I've just been taking a look and I don't immediately see a kernel module that 
provides an interface to GPIO via /dev. I think there's things for I2C etc.


GPIO is managed via a mmap-ped file, which means the usual access mechanisms 
apply.

Michael.
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Re: [fpc-pascal] Access GPIO pins on RPi2 without root?

[Mark Morgan Lloyd]

Jonas Maebe wrote:

Bo Berglund wrote on Wed, 07 Oct 2015:


I think that it really does because there must be some interface
between the FPC system and the underlying operating system managing
the hardware.


On Linux/Unix, every interface to hardware gets exposed as a file 
(generally under /dev). Sometimes you have libraries that provide a 
higher level interface, but in the end it will always access that file. 
If you need root permissions to perform actions on this file with 
language X, you will also need them with language Y and also if you use 
library Z to access it. The file operations are basic POSIX operations 
(open, read, write, ioctl, close), which are available with an "fp" 
prefix via the baseunix and unix units, and which are the same in C or 
other languages.


If you have a library that you want to use, then you can of course ask 
here whether anyone has translated the headers for it (which will 
probably be in C) to Pascal or so.


I've just been taking a look and I don't immediately see a kernel module 
that provides an interface to GPIO via /dev. I think there's things for 
I2C etc.


Via 
http://wiki.freepascal.org/Lazarus_on_Raspberry_Pi#1._Native_hardware_access 
I see mention of /sys/class/gpio etc. although I've not looked to see 
what's implemented as standard. Using this interface requires membership 
of the gpio group, which in principle answers Bo's question.


--
Mark Morgan Lloyd
markMLl .AT. telemetry.co .DOT. uk

[Opinions above are the author's, not those of his employers or colleagues]
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