[C][PPDEV] read parallel port status

From: yvespiel (yvespielusenet_at_free.fr)
Date: 11/23/05

  • Next message: Sebastian Kloska: "Re: Request for Recomandation: Looking for a simple web based costumer relation software" 
    Date: Wed, 23 Nov 2005 12:57:03 +0100

    Hello,
    I'm programming a library in C language in order to read parallel port
    status.
    I use the kernel module ppdev which allow this in userland.
    This library is to be linked with Java through JNI.

    Doc about PPDEV :
    http://people.redhat.com/twaugh/parport/html/ppdev.html
    http://people.redhat.com/twaugh/parport/html/x623.html

    In ppdev programming interface, there is a IOCTL parameter, PPCLAIM.
    IOCTL must be called with this parameter before I can use PPRSTATUS
    which do what I want. With PPCLAIM, I must use PPRELEASE to release the
    port.

    My problem Is that I call PPCLAIM when I open the /dev/parportX ppdev
    device file, and I call PPRELEASE just before I close it. But I see that
    between the PPCLAIM call and the PPRELEASE one, I can send data to /dev/lpX.

    So, now I use PPCLAIM and PPRELEASE just before and after each PPRSTATUS
    call.

    So I wonder if it good to CLAIM and RELEASE the port so often times (I
    read the port status each 100ms) :

    -----------------------------------------------------
    // CLAIM the port
    p.ioct = ioctl(p.fd , PPCLAIM);
                    if(p.ioct != 0){
                            printf("Erreur lors de la réclamation du port parallèle avant
    l'écoute.\nioctl renvoie '%d'\n", p.ioct);
                    }
                    
    // READ the status
                    p.ioct = ioctl(p.fd, PPRSTATUS, &p.status);
                    if(p.ioct != 0){
                            printf("Erreur lors de la récupération du status du port
    parallèle.\nioctl renvoie '%d'\n", p.ioct);
                            p.status = 0;
                    }

    // RELEASE the port
                    p.ioct = ioctl(p.fd, PPRELEASE);
                    if(p.ioct != 0){
                            printf("Erreur lors de la libération du port parallèle après
    l'écoute.\nioctl renvoie '%d'\n", p.ioct);
                    }
    ---------------------------------------------------------------

    is it a good way (it solves my problem since I can send data now while
    I'm listening port) CLAIM and RELEASE port so often ?

    thanks :)

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