function RaspberryPiGPIODemo
% RaspberryPiGPIODemo - Show basic use of GPIO's on RaspberryPi.
%
% Demos full access to the Pi GPIOs.
%
% Accessing the GPIOs as non-root requires the user account
% to be a member of the Unix group 'gpio'. PsychLinuxConfiguration
% should take care of adding your account if you let it do that
% setup for you. The 'gpio' command line utility allows to configure
% aspects of the GPIOs which your code can't control as non-root,
% therefore you'll see multiple system() callouts in this script
% to that helper utility. If the RPiGPIOMex mex file doesn't work
% then you will need to install the 'wiringPi' package to provide
% the required libwiringPi runtime library. On RaspberryPi OS 11 and
% later, wiringPi does not exist anymore, but you may be able to find
% an alternative Debian (armhf) package from the following link:
%
% https://github.com/WiringPi/WiringPi/releases
%
% The demo shows digital i/o by flashing/alternating the two
% LEDs on the RPi 2B, Red power, and green status.
%
% It shows how to efficiently wait for a rising edge
% trigger on Broadcom pin 17, a real GPIO pin on the
% connector. To avoid the need to actually connect
% a switch to the connector, uses internal programmable
% pullup and pulldown resistors to simulate external
% trigger input to the pin.
%
% Please note that the RPiGPIOMex file is just meant as
% a temporary stop-gap solution to get things going, until
% PTB gains a universal I/O driver. Development and support
% of RPiGPIOMex may cease at a future point in time, it may
% even get removed from the distro! Plan accordingly, maybe
% use a M-File wrapper around it to simplify transition to a
% future better I/O driver.
%
% All pin numbers used with RPiGPIOMex are Broadcom GPIO pin
% numbers, not pin numbers on the connector or wiringPi pin numbers!
%
% A nice translation table between connector pins and Broadcom GPIO
% pins can be found on the following website: https://pinout.xyz
% The command 'pinout' in a terminal will also print the pin mapping.
%

% History:
% 26-Jun-2016 mk  Written.
% 22-Jul-2016 mk  Clarify pin numbering more, reference https://pinout.xyz
% 18-Aug-2023 mk  Update for current libwiringPi, remove now defunct demo code.

if ~IsARM || ~exist('RPiGPIOMex', 'file')
  fprintf('This demo only works on the RaspberryPi. Bye.\n');
  return;
end

% Get Pi revision. We only handle > 1 at the moment:
revision = RPiGPIOMex

if revision < 2
  error('Sorry, RaspberryPi models before revision 2 are not yet supported. ');
end

% Broadcom GPIO pin numbers for the led's on the RPi 2B and
% maybe later models? First gen had different pin numbers, hence
% the 2nd gen check above:
redled = 35;
greenled = 47;

% Decouple OS from LEDs so we are alone in the driver seat:
% Not needed for real GPIO pins on the connector...
fprintf('Please enter your sudo password if prompted, to allow LED control on RPi.\n');
system('sudo -S /bin/bash -c ''echo none > /sys/class/leds/led0/trigger''');
system('sudo -S /bin/bash -c ''echo none > /sys/class/leds/led1/trigger''');

% List all pins which are exported for use by non-root applications,
% and their configuration:
system('gpio exports')

% Switch pins to output mode:
RPiGPIOMex(3, redled, 1);
RPiGPIOMex(3, greenled, 1);

% Remember current LED state for restore at end:
oldRed = RPiGPIOMex(0, redled)
oldGreen = RPiGPIOMex(0, greenled)

% Alternate between red and green led for 10 seconds:
timeout = GetSecs + 10;
while GetSecs < timeout
  RPiGPIOMex(1, redled, 1);
  RPiGPIOMex(1, greenled, 0);
  WaitSecs(0.5);
  RPiGPIOMex(1, redled, 0);
  RPiGPIOMex(1, greenled, 1);
  WaitSecs(0.5);
end

% Restore original LED states:
RPiGPIOMex(1, redled, oldRed);
RPiGPIOMex(1, greenled, oldGreen);

% Restore OS control of leds, displaying disc activity
% and state of power supply and system health:
system('sudo -S /bin/bash -c ''echo mmc0 > /sys/class/leds/led0/trigger''');
system('sudo -S /bin/bash -c ''echo input > /sys/class/leds/led1/trigger''');

% Test for efficiently waiting for reception of a trigger
% signal on an input pin.

% Switch pin 17 to input:
RPiGPIOMex(3, 17, 0);

% Pull it low:
RPiGPIOMex(4, 17, -1);
statelow = RPiGPIOMex(0, 17)

% Pull it high to simulate an external rising edge trigger:
RPiGPIOMex(4, 17, +1);
statehi = RPiGPIOMex(0, 17)

% Pull it low again:
RPiGPIOMex(4, 17, -1);
statelow = RPiGPIOMex(0, 17)

% Wait for a rising edge trigger for up to 10 seconds,
% three times in a row:
trigger1 = RPiGPIOMex(5, 17, 10000)
trigger2 = RPiGPIOMex(5, 17, 10000)
trigger3 = RPiGPIOMex(5, 17, 10000)

% Should be high after trigger:
posthi = RPiGPIOMex(0, 17)

% Tristate it:
RPiGPIOMex(4, 17, 0);
statetri = RPiGPIOMex(0, 17)

return;