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139 lines
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139 lines
7.1 KiB
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[#]: subject: "Control your Raspberry Pi with Lua"
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[#]: via: "https://opensource.com/article/23/3/control-your-raspberry-pi-lua"
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[#]: author: "Alan Smithee https://opensource.com/users/alansmithee"
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[#]: collector: "lkxed"
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[#]: translator: " "
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[#]: reviewer: " "
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[#]: publisher: " "
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[#]: url: " "
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Control your Raspberry Pi with Lua
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======
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Lua is a sometimes misunderstood language. It’s different from other languages, like Python, but it’s a versatile extension language that’s widely used in game engines, frameworks, and more. Overall, I find Lua to be a valuable tool for developers, letting them enhance and expand their projects in some powerful ways.
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You can download and run stock Lua as Seth Kenlon explained in his article [Is Lua worth learning][1], which includes simple Lua code examples. However, to get the most out of Lua, it’s best to use it with a framework that has already adopted the language. In this tutorial, I demonstrate how to use a framework called Mako Server, which is designed for enabling Lua programmers to easily code IoT and web applications. I also show you how to extend this framework with an API for working with the Raspberry Pi’s GPIO pins.
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### Requirements
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Before following this tutorial, you need a running Raspberry Pi that you can log into. While I will be compiling C code in this tutorial, you do not need any prior experience with C code. However, you do need some experience with a [POSIX][2] terminal.
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### Install
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To start, open a terminal window on your Raspberry Pi and install the following tools for downloading code using Git and for compiling C code:
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```
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$ sudo apt install git unzip gcc make
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```
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Next, compile the open source Mako Server code and the Lua-periphery library (the Raspberry Pi GPIO library) by running the following command:
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```
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$ wget -O Mako-Server-Build.sh
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https://raw.githubusercontent.com/RealTimeLogic/BAS/main/LinuxBuild.sh \
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```
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Review the script to see what it does, and run it once you’re comfortable with it:
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```
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$ sh ./Mako-Server-Build.sh
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```
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The compilation process may take some time, especially on an older Raspberry Pi. Once the compilation is complete, the script asks you to install the Mako Server and the lua-periphery module to `/usr/local/bin/`. I recommend installing it to simplify using the software. Don’t worry, if you no longer need it, you can uninstall it:
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```
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$ cd /usr/local/bin/
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$ sudo rm mako mako.zip periphery.so
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```
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To test the installation, type `mako` into your terminal. This starts the Mako Server, and see some output in your terminal. You can stop the server by pressing **CTRL+C**.
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### IoT and Lua
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Now that the Mako Server is set up on your Raspberry Pi, you can start programming IoT and web applications and working with the Raspberry Pi’s GPIO pins using Lua. The Mako Server framework provides a powerful and easy API for Lua developers to create IoT applications and the lua-periphery module lets Lua developers interact with the Raspberry Pi’s GPIO pins and other peripheral devices.
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Start by creating an application directory and a `.preload` script, which inserts Lua code for testing the GPIO. The `.preload` script is a Mako Server extension that’s loaded and run as a Lua script when an application is started.
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```
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$ mkdir gpiotst
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$ nano gpiotst/.preload
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```
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Copy the following into the [Nano editor][3] and save the file:
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```
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-- Load periphery.so and access the LED interface
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local LED = require('periphery').LED
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local function doled()
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local led = LED("led0") -- Open LED led0
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trace"Turn LED on"
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led:write(true) -- Turn on LED (set max brightness)
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ba.sleep(3000) -- 3 seconds
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trace"Turn LED off"
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led:write(false) -- Turn off LED (set zero brightness)
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led:close()
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end
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ba.thread.run(doled) -- Defer execution
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-- to after Mako has started
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```
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The above Lua code controls the main Raspberry Pi LED using the Lua-periphery library you compiled and included with the Mako Server. The script defines a single function called `doled` that controls the LED. The script begins by loading the `periphery` library (the shared library periphery.so) using the Lua `require` function. The returned data is a [Lua table][4] with all GPIO API functions. However, you only need the LED API, and you directly access that by appending `.LED` after calling `require`. Next, the code defines a function called `doled` that does the following:
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- Opens the Raspberry Pi main LED identified as `led0` by calling the `LED` function from the `periphery` library and by passing it the string `led0`.
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- Prints the message `Turn LED on` to the trace (the console).
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- Activates the LED by calling the `write` method on the LED object and passing it the Boolean value `true`, which sets the maximum brightness of the LED.
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- Waits for 3 seconds by calling `ba.sleep(3000)`.
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- Prints the message `Turn LED off` to the trace.
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- Deactivates the LED by calling the `write` method on the LED object and passing it the Boolean value `false`, which sets zero brightness of the LED.
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- Closes the `LED` by calling the `close` function on the LED object.
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At the end of the `.preload` script, the `doled` function is passed in as argument to function `ba.thread.run`. This allows the execution of the `doled` function to be deferred until after Mako Server has started.
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To start the `gpiotst` application, run the Mako Server as follows:
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```
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$ mako -l::gpiotst
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```
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The following text is printed in the console:
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```
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Opening LED:
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opening 'brightness': Permission denied.
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```
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Accessing GPIO requires root access, so stop the server by pressing **CTRL+C** and restart the Mako Server as follows:
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```
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$ sudo mako -l::gpiotst
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```
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Now the Raspberry Pi LED turns on for 3 seconds. Success!
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### Lua unlocks IoT
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In this primer, you learned how to compile the Mako Server, including the GPIO Lua module, and how to write a basic Lua script for turning the Raspberry Pi LED on and off. I’ll cover further IoT functions, building upon this article, in future articles.
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You may in the meantime delve deeper into the Lua-periphery GPIO library by reading its [documentation][5] to understand more about its functions and how to use it with different peripherals. To get the most out of this tutorial, consider following the [interactive Mako Server Lua tutorial][6] to get a better understanding of Lua, web, and IoT. Happy coding!
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--------------------------------------------------------------------------------
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via: https://opensource.com/article/23/3/control-your-raspberry-pi-lua
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作者：[Alan Smithee][a]
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选题：[lkxed][b]
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译者：[译者ID](https://github.com/译者ID)
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校对：[校对者ID](https://github.com/校对者ID)
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本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出
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[a]: https://opensource.com/users/alansmithee
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[b]: https://github.com/lkxed/
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[1]: https://opensource.com/article/22/11/lua-worth-learning
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[2]: https://opensource.com/article/19/7/what-posix-richard-stallman-explains
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[3]: https://opensource.com/article/20/12/gnu-nano
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[4]: https://opensource.com/article/22/11/iterate-over-tables-lua
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[5]: https://github.com/vsergeev/lua-periphery/tree/master/docs
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[6]: https://tutorial.realtimelogic.com/Introduction.lsp |