Ubuntu Manpage: pbio — 8255 parallel peripheral interface basic I/O driver

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NAME

       pbio — 8255 parallel peripheral interface basic I/O driver

SYNOPSIS

       device pbio

       In /boot/device.hints:
       hint.pbio.0.at="isa"
       hint.pbio.0.port="0x360"

       #include <dev/pbio/pbioio.h>

DESCRIPTION

The pbio driver supports direct access to the Intel 8255A programmable peripheral interface (PPI) chip
running in mode 0 (simple I/O). Such an interface provides 24 digital I/O lines. The driver is designed
for performing I/O under program control using peripherals such as the Advantech PCL-724 card, which
emulates the Intel 8255A PPI in mode 0. Other 8255A-based peripherals such as the BMC Messsysteme
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 I/O address.

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 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.

A set of 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 I/O in three different
ways:

Basic The read or write operation returns immediately after reading or writing the data to the
port at bus speed.

Paced Data is transferred from or to the port at intervals specified by a separate ioctl(2) call.

Differential (Input only.) Only port values that differ from the previous port value are returned.

The pacing interval is specified in Hz unit increments. Setting a pace of n seconds will result in no
more than one value being read or written every n seconds. Single byte read/write operations will take
at least n seconds to complete.

The following ioctl(2) calls are supported:

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.

PBIO_GETDIFF accepts a pointer to an integer as the third argument, and sets the integer to the last
set value for differential input.

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.

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.

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.

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.

FILES

       /dev/pbio0a   Port A (8 bit I/O).
       /dev/pbio0b   Port B (8 bit I/O).
       /dev/pbio0ch  Port C upper (4 bit I/O).
       /dev/pbio0cl  Port C lower (4 bit I/O).

HISTORY

       The pbio device was first used under FreeBSD 4.1.

AUTHORS

       Diomidis D. Spinellis <dds@aueb.gr>

BUGS

       One of the PCL-724 card's inputs can optionally be wired to generate an interrupt.  This feature  is  not
       supported.

Debian                                          January 14, 2005                                         PBIO(4)