GPIO Binding

Documentation of the GPIO binding bundle

Introduction

Binding for local GPIO subsystem, currently only this exposed to user space by Linux GPIO framework is implemented. Being based on kernel implementation it's hardware agnostic and works on different boards without modification (this is on theory only, not all existing boards can be tested). The difference from other bindings dealing with GPIOs is that it works with GPIO subsystem on the board on which openHAB runs and don't require third-party programs/daemons running. The binding consists of two components: base module (org.openhab.io.gpio) which implements low-level GPIO access and provides API for high-level modules (can be used by other bindings needing to interact directly with GPIOs) and the binding itself (org.openhab.binding.gpio) which introduces hardware GPIO pins as full feature openHAB items capable of generating events or receiving commands depending of their type (input or output).

Prerequisites

1. Linux-based OS with GPIO driver loaded (check whether exists directory /sys/class/gpio), usually it's compiled into the kernel for all recent boards which exposes GPIOs
2. Mounted sysfs pseudo file system, the mount point can be:

• Automatically determined if procfs is mounted under path /proc, this is the default path in almost all configurations
• Manually set in openHAB configuration file, key gpio:sysfs

3. Installed package for native JNA library, e.g. for debian-based OS use apt-get install libjna-java. Version 3.2.7 is used, it's the only available package in Debian currently. If the library isn't in system library path (which is true for most of the cases) you need to add a parameter in command line which starts openHAB and specify the path to JNA library, e.g. edit the last line in "start.sh" and append -Djna.boot.library.path=/usr/lib/jni right after java.

NOTE: Some boards may need additional pin configuration prior using them, for example OMAP-based processors are using pin multiplexing which require changing the mode for some of the pins. Please refer to board's System Reference Manual for more information whether preliminary configuration is needed and how to do it.

Global Binding Configuration

gpio:sysfs - optional directory path where sysfs pseudo file system is mounted. If isn't specified it will be determined automatically (if procfs is mounted under /proc).
gpio:debounce - optional time interval in milliseconds in which pin interrupts for input pins will be ignored to prevent bounce effect seen mainly on buttons. Global option for all pins, can be customized per pin in item configuration. Default value if isn't specified - 0 (zero).

Examples:

gpio:sysfs=/sys
gpio:debounce=10

Item Binding Configuration

Allowed item types are Contact and Switch. Type Contact is used for input pins, Switch - for output pins. The configuration string is following:

gpio="pin:PIN_NUMBER [debounce:DEBOUNCE_INTERVAL] [activelow:yes|no]"

Key-value pairs are separated by space, their order isn't important. Character's case is also insignificant. Key-value pair pin is mandatory, debounce and activelow are optional. If omitted activelow is set to no, debounce - to global option in openHAB configuration file (gpio:debounce) or 0 (zero) if neither is specified. PIN_NUMBER is the number of the pin as seen by the kernel. DEBOUNCE_INTERVAL is the time interval in milliseconds in which pin interrupts for input pins will be ignored to prevent bounce effect seen mainly on buttons. Note that underlying OS isn't real time nor the application is, so debounce implementation isn't something on which you can rely on 100%, you may need to experiment with this value. When activelow is set to no (or omitted) the pins behaves normally: output pins will be set high on ON command and low on OFF, input pins will generate OPEN event when they are high and CLOSED when are low. However, if activelow is set to yes the logic is inverted: when ON command is sent to output pin it will be set to low, on OFF command - to high. Input pins will generate OPEN event when they are low and CLOSED event on high.

Examples:

Switch LED "LED" { gpio="pin:1" }
Switch NormallyClosedRelay "Normally Closed Relay" { gpio="pin:2 activelow:yes" }
Contact NormallyOpenPushButton "Normally Open Push Button" { gpio="pin:3 debounce:10" }
Contact PIR "PIR" { gpio="pin:4 activelow:yes" }
Contact NormallyClosedPushButton "Normally Closed Push Button" { gpio="pin:5 debounce:10 activelow:yes" }