SYNOPSIS

       #include <ieee1284.h>


       int ieee1284_read_control (struct parport *port);

       void ieee1284_write_control (struct parport *port, unsigned char ct);

       void ieee1284_frob_control (struct parport *port, unsigned char mask,
                                   unsigned char val);

       int ieee1284_do_nack_handshake (struct parport *port,
                                       unsigned char ct_before,
                                       unsigned char ct_after,
                                       struct timeval *timeout);

DESCRIPTION

       There are four control lines, three of which are  usually  inverted  on
       PC-style  ports.  Where  they  differ, libieee1284 operates on the IEEE
       1284 values, not the PC-style inverted values. The  control  lines  are
       represented by the following enumeration:

       enum ieee1284_control_bits
       {
         C1284_NSTROBE   = 0x01,
         C1284_NAUTOFD   = 0x02,
         C1284_NINIT     = 0x04,
         C1284_NSELECTIN = 0x08,
         /* To convert those values into PC-style register values, use this: */
         C1284_INVERTED = (C1284_NSTROBE|
                           C1284_NAUTOFD|
                           C1284_NSELECTIN),
       };


       These  functions  all  act  on  the parallel port associated with port,
       which must be claimed.


       The current values on  the  control  lines  are  available  by  calling
       ieee1284_read_control,  and  may  be set by calling ieee1284_write_con-
       trol.


       To adjust the values on a set of control lines, use  ieee1284_frob_con-
       trol.  The  effect  of this can be expressed by: ctr = ((ctr & ~mask) ^
       val); that is, the bits in mask are unset, and then those  in  val  are
       inverted.


       On Linux using the ppdev driver, this is performed by the device driver
       in the kernel, and so is faster than normally possible in a  user-space
       library.

RETURN VALUE

       The return value of ieee1284_read_control, if non-negative, is a number
       representing the value on the control lines.


       Possible error codes for ieee1284_read_control:


       E1284_NOTAVAIL
              The control lines of this port are not accessible by the  appli-
              cation.


       E1284_INVALIDPORT
              The  port  parameter is invalid (for instance, perhaps it is not
              claimed).


       Possible error codes for ieee1284_do_nack_handshake:


       E1284_OK
              The handshake was successful.


       E1284_NOTAVAIL
              This operation is not available on this  port  type  or  system.
              This  could be because port interrupts are not available, or be-
              cause the underlying device driver does not support  the  opera-
              tion.


       E1284_INVALIDPORT
              The  port  parameter is invalid (for instance, perhaps it is not
              claimed).

AUTHOR

       Tim Waugh <twaugh@redhat.com>.



                                                           IEEE1284_CONTROL(3)