Diomidis D. Spinellis, Athens, Greece
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$FreeBSD: releng/11.0/share/man/man4/man4.i386/pbio.4 267938 2014-06-26 21:46:14Z bapt $
.Dd January 14, 2005 .Dt PBIO 4 i386 .Os .Sh NAME .Nm pbio .Nd 8255 parallel peripheral interface basic .Tn I/O driver .Sh SYNOPSIS .Cd "device pbio"
p In
a /boot/device.hints : .Cd hint.pbio.0.at="isa" .Cd hint.pbio.0.port="0x360"
p n dev/pbio/pbioio.h .Sh DESCRIPTION The .Nm 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 BMC Messsysteme .Tn PIO24II card have also been reported to work.
p 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.
p 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.
p 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: l -tag -width ".No Differential" t Basic The read or write operation returns immediately after reading or writing the data to the port at bus speed. t Paced Data is transferred from or to the port at intervals specified by a separate .Xr ioctl 2 call. t Differential (Input only.) Only port values that differ from the previous port value are returned. .El
p The pacing interval is specified in .Em Hz unit increments. Setting a pace of .Ar n seconds will result in no more than one value being read or written every .Ar n seconds. Single byte read/write operations will take at least .Ar n seconds to complete.
p The following .Xr ioctl 2 calls are supported: l -tag -width ".Dv PBIO_SETIPACE" t 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. t 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. t 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. t 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. t 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. t 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 l -tag -width ".Pa /dev/pbio0ch" -compact t Pa /dev/pbio0a Port A (8 bit .Tn I/O ) . t Pa /dev/pbio0b Port B (8 bit .Tn I/O ) . t Pa /dev/pbio0ch Port C upper (4 bit .Tn I/O ) . t Pa /dev/pbio0cl Port C lower (4 bit .Tn I/O ) . .El .Sh SEE ALSO .Rs .%A "Diomidis Spinellis" .%T "The information furnace: Consolidated home control" .%D "2003" .%J "Personal and Ubiquitous Computing" .%N 1 .%V 7 .%P "53-69" .Re .Sh HISTORY The .Nm device was first used under .Fx 4.1 . .Sh AUTHORS .An Diomidis D. Spinellis Aq Mt 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.