Copyright (c) 2000-2002 Diomidis D. Spinellis, Athens, Greece All rights reserved. Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met: 1. Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer as the first lines of this file unmodified. 2. Redistributions in binary form must reproduce the above copyright notice, t...
NAMEpbio - 8255 parallel peripheral interface basic I/O driver
In /boot/device.hints hint.pbio.0.at=isa hint.pbio.0.port=0x360
DESCRIPTIONThe 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:
- 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 )
- "Diomidis Spinellis" "The information furnace: Consolidated home control" "2003" "Personal and Ubiquitous Computing" 1 7 "53-69"