GPIO Driver

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Warning: This article describe the method to use gpio with armadeus version < 4.0. To use gpio on armadeus version 4.0 or more see GPIOlib

On this page, you will find all the informations needed to use the Armadeus GPIO driver.



Since Armadeus-3.0 release, gpio driver is compiled and installed by default in rootfs. See Talk:GPIO_Driver to know how.

You have 2 modules:

  • gpio: this is the main driver. It should be loaded first and will allow you to easily control GPIO pins from user space,
  • ppdev: this is an extension driver to add PPDEV emulation to gpio.ko. This way you will be able to emulate a standard parallel port on one GPIO port (to connect a textual LCD, for example).
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Note: The parallel port driver (ppdev) will only work on APF9328 based systems for now !

Loading driver

 # /usr/bin/

or look inside this script if you want to manually enter the module parameters:

 # modprobe gpio portB_init=0,0,0x00FFFF00,0,0,0,0,0,0x0FF00000,0,0,0,0,0,0,0x0FF00000

gpio module parameters are values for PORTA, PORTB, PORTC, PORTD configuration registers in following order: DDIR, OCR1, OCR2, ICONFA1, ICONFA2, ICONFB1, ICONFB2, DR, GIUS, SSR, ICR1, ICR2, IMR, GPR, SWR, PUEN,

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Warning: If you don't know what these registers means, load the module without parameters !!

Driver usage


GPIO can be use with library AsDevices.

Directly with shell commands (through /proc & /dev filesystem)

GPIO driver is usable through its /proc interface:

  1. use /proc/drivers/gpio/portXmode to configure a pin as a gpio (with echo) and where X is your port name: A, B, C or D (E,F for apf27)
  2. use /proc/drivers/gpio/portXdir to read (with cat) or set (with echo) pin direction (where X is your port name)
  3. then use /proc/drivers/gpio/portX to read (with cat) or write (with echo) pin status
  4. /proc/drivers/gpio/portXirq: to configure GPIO as an interrupt (blocking read); 0-> no interrupt, 1-> rising edge, 2-> falling edge, 3-> both edges
  5. /proc/drivers/gpio/portXpullup: (de)activate i.MX internal pull-up for that GPIO


  • Configure IO-Pin 31 of port A (LCD_OE_ACD on the APF27) as GPIO (not reversible):
 # echo -n 10000000000000000000000000000000 > /proc/driver/gpio/portAmode
  • See which IO-Pins of PortD are configured as inputs, and which one are outputs ('1' = output, '0' = input):
 # cat /proc/driver/gpio/portDdir
 01101100111100000110110011110000       pins order: [31...0]
  • Configure the IO-Pins 30, 28, 23, 22 and 21 of PortB as outputs ('1'), all others as inputs ('0'):
 # echo -n 01010000111000000000000000000000 > /proc/driver/gpio/portBdir
  • Read the status/values of the IOs of PortB:
 # cat /proc/driver/gpio/portB
  • Set bits 30, 28 and 23 of PortB to '1', all other outputs to '0': <-- DEPRECATED, use /dev/gpio/ instead !
 # echo -n 01010000100000000000000000000000 > /proc/driver/gpio/portB
 # cat /proc/driver/gpio/portDmode | sed "s/[0-1]\([0-1]\{31\}\)$/1\1/" > /proc/driver/gpio/portDmode
 # cat /proc/driver/gpio/portDdir | sed "s/[0-1]\([0-1]\{31\}\)$/1\1/" > /proc/driver/gpio/portDdir
 # echo -ne "\x00" > /dev/gpio/PD31
 # echo -ne "\x01" > /dev/gpio/PD31
  • Blinks the LED on APF27Dev (pin 14 of portF):
 # cat /proc/driver/gpio/portFmode | sed "s/[0-1]\([0-1]\{14\}\)$/1\1/" > /proc/driver/gpio/portFmode
 # cat /proc/driver/gpio/portFdir | sed "s/[0-1]\([0-1]\{14\}\)$/1\1/" > /proc/driver/gpio/portFdir
 # echo -ne "\x01" > /dev/gpio/PF14
 # echo -ne "\x00" > /dev/gpio/PF14
  • Sets only bit 5 of portADir to 1:
 # cat /proc/driver/gpio/portAdir | sed "s/[0-1]\([0-1]\{'''5'''\}\)$/'''1'''\1/" > /proc/driver/gpio/portAdir
  • Sets only bit 5 of portADir to 0:
 # cat /proc/driver/gpio/portAdir | sed "s/[0-1]\([0-1]\{'''5'''\}\)$/'''0'''\1/" > /proc/driver/gpio/portAdir
  • You can put it in a shell function:
     cat $PORT | sed "s/[0-1]\([0-1]\{$NB\}\)$/$VAL\1/" > $PORT

 # setbit /proc/driver/gpio/portAdir 5 0
  • Blocking read on the PortD pin 0:
 # cat /dev/gpio/PD0 | less

Directly from a C program with IOCTLs

There is another way to drive GPIO module: with IOCTLs on the right device node (full port).
ioctl() function is using flags to say what must be done:

  • GPIORDDIRECTION for reading direction settings of the corresponding port
  • GPIOWRDIRECTION for writing direction settings
  • GPIORDDATA for reading data on the corresponding port
  • GPIOWRDATA for writing data
  • Etc...

There is a small C example in target/demos/gpio/ that will give you more explanation: blink_led.c

Directly with C program: /proc filesystem

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Note: For performance please use IOCTL instead (see above)

After inserting the GPIO module, /proc entries are created in the filesystem, and so it's possible to directly use some Linux standard functions inside a C program, such as:

  • fopen
  • fwrite
  • fread
  • fclose

A little piece of code is the best way to understand quickly:

    int i;
    unsigned char dummy;
    char buffer[32];
    char * bufferMode="00000000011111111000000000000000";
    char * bufferDir= "00000000011111111000000000000000";
    char * buffer1=   "00000000000000011000000000000000";
    char * buffer2=   "00000000000001100000000000000000";
    char * buffer3=   "00000000000110000000000000000000";
    char * buffer4=   "00000000011000000000000000000000";
    GPIOMODE = fopen("/proc/driver/gpio/portDmode","w");
    fwrite(bufferMode, sizeof(char), strlen(bufferMode), GPIOMODE);
    GPIODIR = fopen("/proc/driver/gpio/portDdir","w");
    fwrite(bufferDir, sizeof(char), strlen(bufferDir), GPIODIR);
    GPIO = fopen("/proc/driver/gpio/portD","w");
    while(1) {            
        fwrite(buffer1, sizeof(char), strlen(buffer1), GPIO);
        fwrite(buffer2, sizeof(char), strlen(buffer2), GPIO);
        fwrite(buffer3, sizeof(char), strlen(buffer3), GPIO);
        fwrite(buffer4, sizeof(char), strlen(buffer4), GPIO);
    return (0);