Aim of this tutorials is about raspberryp pi gpis with c codes. writing some arduino examples with c language.
my test board is raspberrypi B model rev.P2
I have installed raspian to my machine. I will test on it. raspian is easy to install, and a full linux distrubition. preparing a test on raspian is so fast. at the end, I have to say that, raspian is a big embedded installation. starting a raspian is long about 5 seconds. using raspian at a commercial project, is not a good decision. compiling a custom kernel,and create a custom linux can be better. of course I must say that, linux is not a RTOS. some linux RTOS distribution exits. search them for better results.
as you know raspberry have some different configured boards. all boards have a model name and revision number. because of this you must correct your pin number from internet.
I will use B model rev P2.
my raspi has 26 total pins. 2 of them 5V, 2 of them 3.3V, 5 of them GROUND, at the end 26-9=17 gpio pins I have.
as you see above, 17 gpio pins.
of course some of them can be use for different functionalities. sample
for serial connection RxD ve Txd, for I2C ……
as you see below some of them can be assigned for different functionalities.
I will change above table a little. I will give from left to right a number. And I will define pins with that names
with linux it is so easy to test this pins. for testing you don’t need to code.
at linux console
if you cannot enter , kernel does not support gpio sysfs. compile kernel with gpio sysfs.
in linux there is lots of file systems like devpts, sysfs, proc etc….
with these files and directiories you can get lots of information about linux,working processes, devices etc… these file systems are a bridge with kernel space and user space. (search kernel space, user space)
kernel documentation about gpio sysfs
if everything is good, lets continues
you will see 3 files below
export unexport gpiochip0
export you can open a pin
unexport you can close a pin
opening pin 2
echo 2 > export
echo 2 > unexport
echo 2 >export
you will see a directory -> gpio2
ls -> you will see below
active_low device direction edge power subsystem uevent value
some of them file some of directories
direction-> values accepted “in” or “out”
echo “in” > direction pin is input mode
echo “out”> direction pin is output mode
value-> 0 (low) or 1 (high)
echo “1” >value
active_low-> default 0 low 1 high means
edge->“none”, “rising”, “falling”, or “both” getting information about pin. expecialy using with poll or select etc…
uevent-> ? I could not find any information, Anyone knows?
I have added linux pin numbers to table.
example GPIO_3 pin is 14 linux pin number
you can control GPIO_3 with
echo 14 >export
cd gpio etc ………
lets create a simple led circuit below
restart your raspi for a fresh start
echo 14 > export
echo “out” > direction
echo 1 >value
echo 1 >value