188 lines
5.5 KiB
Groff
188 lines
5.5 KiB
Groff
.\" Copyright (c) 2000-2002
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.\" Diomidis D. Spinellis, Athens, Greece
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.\" All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer as
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.\" the first lines of this file unmodified.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY Diomidis D. Spinellis ``AS IS'' AND ANY
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.\" EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
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.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL Diomidis D. Spinellis BE
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.\" LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR
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.\" BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
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.\" WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE
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.\" OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE,
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.\" EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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.\"
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.\" $FreeBSD$
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.\"
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.Dd January 14, 2005
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.Dt PBIO 4 i386
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.Os
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.Sh NAME
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.Nm pbio
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.Nd 8255 parallel peripheral interface basic
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.Tn I/O
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driver
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.Sh SYNOPSIS
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.Cd "device pbio"
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.Pp
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In
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.Pa /boot/device.hints :
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.Cd hint.pbio.0.at="isa"
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.Cd hint.pbio.0.port="0x360"
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.Pp
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.In dev/pbio/pbioio.h
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.Sh DESCRIPTION
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The
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.Nm
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driver supports direct access to the Intel 8255A programmable
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peripheral interface (PPI) chip running in mode 0 (simple
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.Tn I/O ) .
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Such an interface provides 24 digital
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.Tn I/O
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lines.
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The driver is designed for performing
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.Tn I/O
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under program control using
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peripherals such as the
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.Tn Advantech
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.Tn PCL-724
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card, which emulates the Intel 8255A PPI in mode 0.
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Other 8255A-based peripherals such as the
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.Tn BMC
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Messsysteme
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.Tn PIO24II
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card have also been reported to work.
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.Pp
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The PPI provides two 8-bit ports (port A and port B) and
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two 4-bit ports (port C upper, port C lower).
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Each port can be individually programmed for input and
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(latched) output,
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and appears at a different offset of the device's base
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.Tn I/O
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address.
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.Pp
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A separate register allows the configuration of ports for input
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or output.
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The device is so simple, that reliably probing for it when
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input data arrives at its terminals is impossible;
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therefore the kernel configuration has to specify the
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device's base address.
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The device driver provides four character devices that
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correspond to the peripheral's
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.Tn I/O
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ports.
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Opening a device for read or write automatically configures
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the corresponding hardware port for input or output.
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At boot time all ports are set configured for input to avoid damaging
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external circuitry.
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.Pp
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A set of
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.Xr ioctl 2
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requests allow polled input and paced output to be
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efficiently performed at the driver level without expensive
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user/kernel context switching.
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The driver can perform
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.Tn I/O
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in three different ways:
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.Bl -tag -width ".No Differential"
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.It Basic
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The read or write operation returns immediately after reading
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or writing the data to the port at bus speed.
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.It Paced
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Data is transferred from or to the port at intervals specified
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by a separate
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.Xr ioctl 2
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call.
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.It Differential
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(Input only.)
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Only port values that differ from the previous port value are returned.
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.El
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.Pp
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The pacing interval is specified in
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.Em Hz
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unit increments.
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Setting a pace of
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.Ar n
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seconds
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will result in no more than one value being read or written every
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.Ar n
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seconds.
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Single byte read/write operations will take at least
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.Ar n
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seconds to complete.
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.Pp
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The following
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.Xr ioctl 2
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calls are supported:
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.Bl -tag -width ".Dv PBIO_SETIPACE"
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.It Dv PBIO_SETDIFF
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accepts a pointer to an integer as the third argument,
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and sets the driver for differential input if the integer is non-zero.
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The input pace speed determines the periodic interval the driver will use to
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examine the port for a changed value.
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.It Dv PBIO_GETDIFF
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accepts a pointer to an integer as the third argument,
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and sets the integer to the last set value for differential input.
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.It Dv PBIO_SETIPACE
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accepts a pointer to an integer as the third argument,
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and sets the driver's input pacing speed to the value of that integer.
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.It Dv PBIO_GETIPACE
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accepts a pointer to an integer as the third argument,
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and sets the integer to the last set value for the input pace.
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.It Dv PBIO_SETOPACE
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accepts a pointer to an integer as the third argument,
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and sets the driver's output pacing speed to the value of that integer.
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.It Dv PBIO_GETOPACE
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accepts a pointer to an integer as the third argument,
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and sets the integer to the last set value for the output pace.
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.El
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.Sh FILES
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.Bl -tag -width ".Pa /dev/pbio0ch" -compact
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.It Pa /dev/pbio0a
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Port A (8 bit
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.Tn I/O ) .
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.It Pa /dev/pbio0b
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Port B (8 bit
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.Tn I/O ) .
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.It Pa /dev/pbio0ch
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Port C upper (4 bit
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.Tn I/O ) .
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.It Pa /dev/pbio0cl
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Port C lower (4 bit
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.Tn I/O ) .
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.El
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.Sh SEE ALSO
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.Rs
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.%A "Diomidis Spinellis"
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.%T "The information furnace: Consolidated home control"
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.%D "2003"
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.%J "Personal and Ubiquitous Computing"
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.%N 1
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.%V 7
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.%P "53-69"
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.Re
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.Sh HISTORY
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The
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.Nm
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device was first used under
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.Fx 4.1 .
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.Sh AUTHORS
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.An Diomidis D. Spinellis Aq Mt dds@aueb.gr
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.Sh BUGS
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One of the
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.Tn PCL-724
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card's inputs can optionally be wired to generate an interrupt.
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This feature is not supported.
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