GPIO Input value won't change from Userspace

[Saad Zia]

Dear Experts

I am using Petalinux 2015.4 and Zedboard. I am reading a GPIO which is supposed to go from 0 to 1 and in commandline, I can see that it happens. But when I execute it in the code, the value always remain 0 as initial value is 0. My code is as follows:

int number=-1;
    unsigned char error = 0;
    int fd_done;
    //Export GPIO
    fd_done = open("/sys/class/gpio/export", O_WRONLY);
    if(fd_done < 0)
    {
#if DEBUG_GPIOBit
        printf("ERROR:\tGPIO Export Failed\n\r");
#endif
        error=1;
    }
    write(fd_done,"903",3);
    close(fd_done);
    //Set GPIO as input
    fd_done = open("/sys/class/gpio/gpio903/direction", O_WRONLY);
    if(fd_done < 0)
    {
#if DEBUG_GPIOBit
        printf("ERROR:\tGPIO Direction Failed\n\r");
#endif
        error=1;
    }
    write(fd_done,"in",2);
    close(fd_done);
    
    char value;
    fd_done = open("/sys/class/gpio/gpio903/value", O_WRONLY);
    lseek(fd_done, 0, SEEK_SET);
    read(fd_done, &value, 8);
    printf("Done Value: \t %d \n",value);
    close(fd_done);
    fd_done = open("/sys/class/gpio/unexport", O_WRONLY);
    write( fd_done,"903",3);
    close(fd_done);
    return number;

[Saad Zia]

the issue was solved by changing fd_done = open("/sys/class/gpio/gpio903/value", O_WRONLY); to fd_done = open("/sys/class/gpio/gpio903/value", 2);

[jpeyron]

Hi @Saad Zia,

Here is a link to the Xilinx Wiki- GPIO User space app that has should help with your code.

cheers,

Jon

[jpeyron]

Hi @Saad Zia,

Glad to hear you solved the issue. Thank you for sharing the solution!

cheers,

Jon