.\"  Copyright (c) 2000-2002
.\"          Diomidis D. Spinellis, Athens, Greece
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.Dd February 19, 2003
.Dt PBIO 4 i386
.Os
.Sh NAME
.Nm pbio
.Nd 8255 parallel peripheral interface basic
.Tn I/O
driver
.Sh SYNOPSIS
.Cd "device pbio0 at isa? port 0x360"
.In machine/pbioio.h
.Sh DESCRIPTION
The
.Xr pbio 4
driver supports direct access to the Intel 8255A programmable
peripheral interface (PPI) chip running in mode 0 (simple
.Tn I/O ) .
Such an interface provides 24 digital
.Tn I/O
lines.
The driver is designed for performing
.Tn I/O
under program control using
peripherals such as the
.Tn Advantech
.Tn PCL-724
card, which emulates the Intel 8255A PPI in mode 0.
Other 8255A-based peripherals such as the
.Tn bmcm
.Tn PIO24II
card have also been reported to work.
The PPI provides two 8-bit ports (port A and port B) and
two 4-bit ports (port C upper, port C lower).
Each port can be individually programmed for input and
(latched) output and appears at a different offset of the device's
base
.Tn I/O
address.
.Pp
A separate register allows the configuration of ports for input
or output.
The device is so simple, that reliably probing for it when
input data arrives at its terminals is impossible;
therefore the kernel configuration has to specify the
device's base address.
The device driver provides four character devices that
correspond to the peripheral's
.Tn I/O
ports.
Opening a device for read or write, automatically configures
the corresponding hardware port for input or output.
At boot time all ports are set configured for input to avoid damaging
external circuitry.
.Pp
A set of
.Xr ioctl 2
requests allow polled input and paced output to be
efficiently performed at the driver level without expensive
user/kernel context switching.
The driver can perform
.Tn I/O
in three different ways:
.Bl -tag -width Differential
.It Basic
The read or write operation returns immediately after reading
or writing the data to the port at bus speed.
.It Paced
Data is transferred from or to the port at intervals specified
by a separate
.Xr ioctl 2
call.
.It Differential
(Input only.)
Only port values that differ from the previous port value are returned.
.El
.Pp
The pacing interval is specified in
.Em Hz
unit increments.
Setting a pace of
.Sy n
seconds
will result in no more than one value being read or written every
.Sy n
seconds.
Single byte read/write opeations will take at least
.Sy n
seconds to complete.
.Pp
The following
.Xr ioctl 2
calls are currently supported:
.Bl -tag -width "PBIO_SETIPACE"
.It Dv PBIO_SETDIFF
accepts a pointer to an integer as the third argument and sets
the driver for differential input if the integer is non-zero.
The input pace speed determines the periodic interval the driver will use to
examine the port for a changed value.
.It Dv PBIO_GETDIFF
accepts a pointer to an integer as the third argument and sets
the integer to the last set value for differential input.
.It Dv PBIO_SETIPACE
accepts a pointer to an integer as the third argument and sets
the driver's input pacing speed to the value of that integer.
.It Dv PBIO_GETIPACE
accepts a pointer to an integer as the third argument and sets
the integer to the last set value for the input pace.
.It Dv PBIO_SETOPACE
accepts a pointer to an integer as the third argument and sets
the driver's output pacing speed to the value of that integer.
.It Dv PBIO_GETOPACE
accepts a pointer to an integer as the third argument and sets
the integer to the last set value for the output pace.
.El
.Sh FILES
.Bl -tag -width "/dev/pbioxxx"
.It Pa /dev/pbio0a
Port A (8 bit
.Tn I/O ) .
.It Pa /dev/pbio0b
Port B (8 bit
.Tn I/O ) .
.It Pa /dev/pbio0ch
Port C upper (4 bit
.Tn I/O ) .
.It Pa /dev/pbio0cl
Port C lower (4 bit
.Tn I/O ) .
.El
.Sh SEE ALSO
.Rs
.%A "Diomidis Spinellis"
.%T "The information furnace: User-friendly home control"
.%B "Proceedings of the  3rd International System Administration and Networking Conference SANE 2002"
.%P "145-174"
.%O "Maastricht, The Netherlands"
.%D "May 2002"
.Re
.Sh HISTORY
The
.Nm
device was first used under
.Fx 4.1 .
.Sh AUTHOR
.An "Diomidis D. Spinellis" Aq dds@aueb.gr
.Sh BUGS
One of the
.Tn PCL-724
card's inputs can optionally be wired to generate an interrupt.
This feature is not supported.