|PBIO(4)||FreeBSD Kernel Interfaces Manual (i386)||PBIO(4)|
NAMEpbio — 8255 parallel peripheral interface basic I/O driver
#include < dev/pbio/pbioio.h>
DESCRIPTIONThe 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:
- The read or write operation returns immediately after reading or writing the data to the port at bus speed.
- Data is transferred from or to the port at intervals specified by a separate ioctl(2) call.
- (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:
- 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.
- accepts a pointer to an integer as the third argument, and sets the integer to the last set value for differential input.
- accepts a pointer to an integer as the third argument, and sets the driver's input pacing speed to the value of that integer.
- accepts a pointer to an integer as the third argument, and sets the integer to the last set value for the input pace.
- accepts a pointer to an integer as the third argument, and sets the driver's output pacing speed to the value of that integer.
- accepts a pointer to an integer as the third argument, and sets the integer to the last set value for the output pace.
- Port A (8 bit I/O).
- Port B (8 bit I/O).
- Port C upper (4 bit I/O).
- Port C lower (4 bit I/O).
SEE ALSODiomidis Spinellis, The information furnace: Consolidated home control, Personal and Ubiquitous Computing, 1, 7, 53-69, 2003.
HISTORYThe pbio device was first used under FreeBSD 4.1.
BUGSOne of the PCL-724 card's inputs can optionally be wired to generate an interrupt. This feature is not supported.
|January 14, 2005||FreeBSD|