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IEEE1284_CONTROL(3) IEEE1284_CONTROL(3)
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_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.
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 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)
Man(1) output converted with
man2html and wrapped by fishsponge
This page was generated on Sat Sep 8 16:37:39 GMT 2007
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