pbio (4)
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Copyright (c) 2000-2002
Diomidis D. Spinellis, Athens, Greece
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NAME
pbio - 8255 parallel peripheral interface basic I/O driverSYNOPSIS
device pbioIn /boot/device.hints hint.pbio.0.at=isa hint.pbio.0.port=0x360
In dev/pbio/pbioio.h
DESCRIPTION
The ifconfig 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 )
SEE ALSO
- "Diomidis Spinellis" "The information furnace: Consolidated home control" "2003" "Personal and Ubiquitous Computing" 1 7 "53-69"