Difference between revisions of "GPIO Driver"

Revision as of 14:56, 26 August 2009

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

Compilation

Done by default starting from Armadeus-3.0 release. See Talk:GPIO_Driver to know how.

Installation

When compiled, you will 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: The parallel port driver (ppdev) will only work on APF9328 based systems !

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

Driver usage

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

GPIO driver is configurable through /proc interface:

• 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)
• use /proc/drivers/gpio/portXdir to read (with cat) or set (with echo) pin direction (where X is your port name)
• then use /proc/drivers/gpio/portX to read (with cat) or write (with echo) pin status
• /proc/drivers/gpio/portXirq: configure if GPIO should be used as an interruptible one (ie blocking read)
• /proc/drivers/gpio/portXpullup: (de)activate i.MXL internal pull-up for that GPIO

Examples:

• Configure IO-Pin 31 of port A (LCD_OE_ACD on the APF27) as gpio

 # 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

• Blinks the LED on APF9328DevFull (pin 31 of portD):

 # 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

• 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

Directly with C program ( /proc filesystem)

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);

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

Links

• http://soekris.hejl.de/
• http://people.redhat.com/twaugh/parport/html/ppdev.html
• http://www.krugle.com/examples/p-yckfcEKjgfqvsNcB/drivertest.c
• AT91 way of doing it
• AVR32 way of doing it
• JiBee's way of doing it