chardevgpio

chardevgpio

chardevgio is a pure Go library for access the Linux GPIO character device user API.

Usage

import gpio "github.com/vinymeuh/chardevgpio"

In following examples, error handling will be ommited.

Chip

A Chip object must be open before to request lines or lines informations from a GPIO chip.

chip, _ := gpio.NewChip("/dev/gpiochip0")
...
defer chip.Close()

Closing a chip does not invalidate any previously requested lines that can still be used.

LineInfo

Lines information can be requested from the chip at any moment as long as it is open.

li, _ := chip.LineInfo(0)
line0Name := li.Name()

HandleRequest

An HandleRequest is mandatory to setup a request an input line or an output line from the chip. The request should at minimum define the offsets of requested lines and the communication direction.

lineIn_0, _    := chip.NewHandleRequest([]int{0}, gpio.HandleRequestInput)
lineOut_8_9, _ := chip.NewHandleRequest([]int{8, 9}, gpio.HandleRequestOutput)

Consumer name or default values can be set on the HandleRequest:

lineIn_0.WithConsumer("myapp")
lineOut_8_9.WithDefaults([]int{1, 1})

Requesting lines to the chip is done passing a reference to the HandleRequest to Chip.RequestLines():

c.RequestLines(lineIn_0)
c.RequestLines(lineOut_8_9) 

If no errors, the returned HandleRequest can then be used to read from or write to the lines:

val0 := lineIn_0.Read()
lineOut_8_9.Write(0, 0)

Note that HandleRequest.Read() returns 3 values:

• first one is the read value for the first line managed by the HandleRequest. It is useful when working on a request with only one line.
• second one is an array containing read values for all lines managed by the HandleRequest
• last one is the error if any

LineWatcher

Event on an input line can be trapped using a LineWatcher:

watcher, _ := gpio.NewLineWatcher()

Add to it lines and events to be watched:

watcher.Add(c, 0, gpio.RisingEdge, "wait rising edge on line 0")
watcher.Add(c, 1, gpio.FallingEdge, "wait falling edge on line 1")
watcher.Add(c, 2, gpio.BothEdges, "wait state change on line 2")

The watcher can then run indefinitely and call a handler function for each event trapped:

func myFuncHandler(evd Event) { ... }
watcher.WaitForEver(myFuncHandler)

For simpler cases, the watcher can be used to block waiting for the first event occurrence:

event, _ := watcher.Wait()

Tests

During development, the library is tested using the Linux kernel module gpio-mockup on an x86_64 environment.

> ./setup-test.sh   # to be run once, prompts for sudo password
> make test

For real world tests on a Raspberry, see command line utilities provided under cmd directory.