ieee1284_do_nack_handshake (3)
Leading comments
Title: ieee1284_control
Author: Tim Waugh <twaugh@redhat.com>
Generator: DocBook XSL Stylesheets v1.72.0 <http://docbook.sf.net/>
Date: 09/18/2007
Manual: Functions
Source:
NAME
ieee1284_read_control, ieee1284_write_control, ieee1284_frob_control, ieee1284_do_nack_handshake - manipulate control linesSYNOPSIS
#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);
- void ieee1284_write_control(struct parport *port, unsigned char ct);
DESCRIPTION
-
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.