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https://github.com/kopera/erlang-gpio
An Erlang application for interfacing with GPIOs on Linux systems.
https://github.com/kopera/erlang-gpio
embedded erlang gpio linux
Last synced: 27 days ago
JSON representation
An Erlang application for interfacing with GPIOs on Linux systems.
- Host: GitHub
- URL: https://github.com/kopera/erlang-gpio
- Owner: kopera
- License: apache-2.0
- Created: 2020-07-06T08:45:55.000Z (over 4 years ago)
- Default Branch: main
- Last Pushed: 2023-04-03T04:32:58.000Z (over 1 year ago)
- Last Synced: 2024-09-16T17:46:13.190Z (about 2 months ago)
- Topics: embedded, erlang, gpio, linux
- Language: Erlang
- Homepage:
- Size: 39.1 KB
- Stars: 12
- Watchers: 3
- Forks: 2
- Open Issues: 4
-
Metadata Files:
- Readme: README.md
- License: LICENSE
Awesome Lists containing this project
README
# gpio
An Erlang application for interfacing with GPIOs on Linux systems.
This GPIO application allows for reading and writing to GPIO pins as well as
monitoring input GPIO pins.
# Setup
You need to add `gpio` as a dependency to your project. If you are using
`rebar3`, you can add the following to your `rebar.config`:
```erlang
{deps, [
{gpio, "0.6.3"}
]}.
```
Also ensure that `gpio` is added as a dependency to your application, by
updating your `.app.src` file:
```erlang
{application, my_app, [
{applications, [
kernel,
stdlib,
gpio % <- You need this in your applications list
]}
]}.
```
# Usage
## Opening the gpio chip
The following will open gpiochip2 (typically called GPIO3):
```erlang
> {ok, Chip} = gpio:open_chip("/dev/gpiochip2").
{ok, #Ref<0.3061467712.2848194561.68326>}
```
Once the chip is open you need to either use `gpio:open_lines/5` if you want
to read/write values to/from the lines, or `gpio:open_line_events/5` if you want
to monitor a line.
## Opening gpio lines
The following will open a single line `IO1` from the previously open
chip (typically this would be `GPIO3_IO1`). The opened line is configured as an
output with a default value of `0`. The last parameter is used to communicate
to the kernel a description of the chip use. If `debugfs` is enabled, this
information is visible in `/sys/kernel/debug/gpio`.
```erlang
> {ok, SingleLine} = gpio:open_lines(Chip, [1], [output], [0], "my-application").
{ok, #Ref<0.3061467712.2848194561.68334>}
```
To write a `0` to the GPIO line, you can use:
```erlang
ok = gpio:write_lines(SingleLine, {0}).
```
Alternatively, to write a `1` to the GPIO line, you can use:
```erlang
ok = gpio:write_lines(SingleLine, {1}).
```
The `gpio:write_lines/2` function takes a tuple of `0` and `1` values. The arity
of this tuple must be equal to the width of the lines. Previously, we opened a
single line, which is why we use a single element tuple. If instead, we opened
2 lines, we would need to provide a 2 element tuple like below:
```erlang
> {ok, MultiLines} = gpio:open_lines(Chip, [1, 2, 5], [output], [0, 0, 0], "my-application").
{ok, #Ref<0.3061467712.2848194561.68339>}
> ok = gpio:write_lines(MultiLines, {1, 1, 1}). % Set all pins to 1
ok
> ok = gpio:write_lines(MultiLines, {1, 0, 1}). % Set IO1 and IO5 to 1, IO2 is set to 0
ok
```
## Monitoring line events
The following will monitor the pin `IO10` (`GPIO3_I10`) for rising values
(changes from 0 to 1).
```erlang
> {ok, LineEvents} = gpio:open_line_events(Chip, 10, [], [rising_edge], "my-application").
{ok, {#Ref<0.3061467712.2848194561.68344>, <0.340.0>}}
```
The monitoring process will then receive messages like the following:
```erlang
{gpio, LineEvents, {event, Timestamp, Type}}
```
Where `Timestamp` is a system timestamp in nanosecond, and `Type` is either
`rising_edge` or `falling_edge`.
In case of an error, the process might receive a message like the following:
```erlang
{gpio, LineEvents, {error, Error}}
```