IEEE1284_CONTROL

Section: Functions (3)
Updated: 07/26/2009
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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.