NAME
ieee1284_read_control, ieee1284_write_control, ieee1284_frob_control,
ieee1284_do_nack_handshake - manipulate control lines
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_control.
To adjust the values on a set of control lines, use
ieee1284_frob_control. 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.
The special function ieee1284_do_nack_handshake is for responding very
quickly in a protocol where the peripheral sets nAck and the host must
respond by setting a control line. Its operation, which relies on the
host machine knowing which interrupt nAck generates, is as follows:
1. Set the control lines as indicated in ct_before.
2. Wait for nAck interrupt. If timeout elapses, return
E1284_TIMEDOUT.
3. Set the control lines as indicated in ct_after.
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
application.
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 because the
underlying device driver does not support the operation.
E1284_INVALIDPORT
The port parameter is invalid (for instance, perhaps it is not
claimed).
AUTHOR
Tim Waugh <twaugh@redhat.com>
Author.
COPYRIGHT
Copyright © 2001-2003 Tim Waugh
09/18/2007 IEEE1284_CONTROL(3)