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home | helpPBIO(4) FreeBSD/i386 Kernel Interfaces Manual PBIO(4) 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 per- forming 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 out- put. The device is so simple, that reliably probing for it when input data arrives at its terminals is impossible; therefore the kernel config- uration has to specify the device's base address. The device driver pro- vides 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 read- ing or writing the data to the port at bus speed. Paced Data is transferred from or to the port at intervals speci- fied by a separate ioctl(2) call. Differential (Input only.) Only port values that differ from the previ- ous 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", Personal and Ubiquitous Computing, 1, 7, 53-69, 2003. 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. FreeBSD 6.0 January 14, 2005 FreeBSD 6.0
NAME | SYNOPSIS | DESCRIPTION | FILES | SEE ALSO | HISTORY | AUTHORS | BUGS
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