GPIO Driver

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Warning 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.

Contents

Installation

Compilation

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).
Note Note: The parallel port driver (ppdev) will only work on APF9328 based systems for now !


Loading driver

 # /usr/bin/loadgpio.sh

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,

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


Driver usage

As_devices

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

Examples

  • 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
 00000000000011111111000000000000
 #
  • 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:
 setbit()
 {
     PORT=$1
     NB=$2
     VAL=$3
     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
  • A test script is available in target/test/ : test_gpio.sh

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

Note 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;
    FILE *GPIO,*GPIODIR, *GPIOMODE;
    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");
    setvbuf(GPIOMODE,buffer,_IONBF,32);
    fwrite(bufferMode, sizeof(char), strlen(bufferMode), GPIOMODE);
    fclose(GPIOMODE);
    GPIODIR = fopen("/proc/driver/gpio/portDdir","w");
    setvbuf(GPIODIR,buffer,_IONBF,32);
    fwrite(bufferDir, sizeof(char), strlen(bufferDir), GPIODIR);
    fclose(GPIODIR);
    GPIO = fopen("/proc/driver/gpio/portD","w");
    setvbuf(GPIO,buffer,_IONBF,32);
    while(1) {            
        fwrite(buffer1, sizeof(char), strlen(buffer1), GPIO);
        sleep(1);
        fwrite(buffer2, sizeof(char), strlen(buffer2), GPIO);
        sleep(1);
        fwrite(buffer3, sizeof(char), strlen(buffer3), GPIO);
        sleep(1);
        fwrite(buffer4, sizeof(char), strlen(buffer4), GPIO);
        sleep(1);
    }
    fclose(GPIO);
    return (0);

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