Enable an RPi to serve as an ioT gateway for our P2 Hardware - while dedicating only 2 pins for serial communication
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Additional pages:
- Main Page
- Technology/Tools Used (this page)
- Developing your own P2 Application using IoT gateway services
We use a simple Full-duplex serial link between your P2 board and the Raspberry Pi. We've crafted two .spin2 objects which are compiled into your code (The gateway object and a serial line-receiving queue object.) To configure the gateway you specify which two P2 pins are to be used when communicating with the RPi and iidenitfy the application running the gateway.
To use this in your own project you simply compile-in the gateway objects, start it and then make calls to it.
The following objects are compiled into your app.
- isp_rpi_iot_gw.spin2
- isp_queue_serial.spin2
- jm_serial.spin2
- jm_nstrings.spin2
I have two different approaches when developing Spin2/Pasm2 code. When I'm working on a new project doing stuff that I've not done before I'll do my compilation and download/flashing with Propeller Tool and/or PNut running on windows. When I'm expanding a project or making minor tweaks I'll then use FlexProp on my mac desktop or on one of my RPi's for compilation and download/flashing.
But, I'm doing all of my Spin2/Pasm2 editing in Visual Studio Code (VSCode) which I run on my desktop. But where are the files I'm editing??
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If I'm targeting my Windows machine for compile and download I place my project files in a Dropbox folder which the windows machine also shares. I save my changes from my VSCode and then on the Windows machine I run Propeller Tool/PNut to compile and download.
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If, instead, I'm running with my P2 hardware attached to my Mac or an RPi then I'm editing in VSCode and I've configured the VSCode to compile and download the code using the FlexProp compiler/downloader. My Spin2/Pasm2 source files are on the RPi or on my Mac (along with FlexProp). If my files are on the RPi then my VSCode is remoted into the RPi working on files on the RPi itself.
VSCode extensions supporting my efforts:
| VSCode Extension | Purpose |
|---|---|
| Spin2 | Spin2/Pasm2 syntax/semantic hightlighting |
| Remote - SSH | work remotely via SSH |
| Remote - SSH: Editing Configuration Files | Edit config files remotely via SSH |
On the RPi we have a single Python3 script which is run interactively (or from power-on as Daemon) which listens to the serial traffic arriving from the P2. It validates the requests coming from the P2, and then acts on the request. Validation status and, optionally, requested data are returned to the P2 for each request.
The Daemon script also watches for directory changes (files to be modified or new files appearing) in the Control directory. Web pages that want to send values to our P2 write to this Control directory. The P2 application tells the RPi if it wants to be told of changes to specific files on the RPi. If the RPi knows that the P2 is listening and the file is changed the RPi sends each KV pair found in the changed file to the waiting P2.
I'm doing all of my Python editing in Visual Studio Code (VSCode) which I run on my desktop and remote into my RPi containing the python scripts using SSH. In order to use SSH to get into my RPi's I have the following extensions installed into VSCode:
VSCode extensions supporting my efforts:
| VSCode Extension | Purpose |
|---|---|
| Remote - SSH | work remotely via SSH |
| Remote - SSH: Editing Configuration Files | Edit config files remotely via SSH |
| Python | |
| Python Extension Pack | |
| Python Indent |
I use the following references when needing to do something I haven't before in the Python language:
| Language | References |
|---|---|
| Python | |
| Python Tutorial/Ref. at W3 Schools | |
| python.org docs | |
| Python Package Index for when I need new libraries/frameworks for use with python |
Now that you've set up your RPi per our instructions you have the Apache2 web server running on the RPi and you have the PHP interpreter installed.
In order to provide interaction with our P2 we write our RPi web pages in PHP. In most simple cases we have a single index.php file (web page interpreted source) placed in a directory under the web server. But what is a php file?
- PHP files can contain text, HTML, CSS, JavaScript, and PHP code
- PHP code is executed on the server, and the result is returned to the browser as plain HTML
- PHP files have extension ".php"
In other words, the index.php file is comprised of HTML code styled using CSS (typically as included files) and has PHP code intermixed with the HTML. This entire file when requested by a browser is first interpreted by the PHP Interpreter and the resulting HTML is returned to the browser.
In our gateway web pages we use PHP to:
- Load
statusfiles which contain 1 or more KV pairs - Load
procfiles which contain 1 or more KV pairs - Write
controlfiles which also contain 1 or more KV pairs - Retrieve values from HTML/PHP forms
As an example (taken from our web-control demo) here are the actions behind the web page controlling the LED string attached to the P2
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The PHP code loads the values sent from the P2 and uses them as default values for the form it presents. It also loads details about the host RPi on which it is running and shows these details.
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When you adjust the controls on the form and then press [Submit] all values you have set are then written into a control file as key-value pairs. The values placed in the file are shown below the form so you can see what is written to the file.
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The P2, when it started up, notified the RPi that it wanted to hear about any changes made to the control file (which the web-page writes to.)
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The Daemon sees that the file changed (since the web page just wrote to it), loads the KV pairs from the file and then sends them to the P2.
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Lastly the P2 evaluates the change as they arrive and tells the LED string what to change (Color, light pattern, delay, etc.)
I run on a Mac desktop. My favorite tool for creating web pages is Bootstrap Studio This tool provides easy WYSIWYG editing, easy CSS styling, good responsive layout code (pages you create can display well on mobile devices), and exports tiny files for you to place on your server.
However, I edit the PHP and make final tweaks to the HTML/CSS by hand. Yes I'm doing all of the "by hand editing" in Visual Studio Code (VSCode) which I run on my desktop and remote into my RPi containing the pages using SSH. In order to use SSH to get into my RPi's I have the following extensions installed into VSCode:
VSCode extensions supporting my efforts:
| VSCode Extension | Purpose |
|---|---|
| Remote - SSH | work remotely via SSH |
| Remote - SSH: Editing Configuration Files | Edit config files remotely via SSH |
I use the following references when needing to do something I haven't before in each language:
| Language | References |
|---|---|
| HTML | |
| HTML Tutorial/Ref. at W3 Schools | |
| JavaScript Tutorial/Ref. at W3 Schools | |
| Bootstrap Tutorial/Ref. at W3 Schools (Pick the version you use) | |
| CSS | |
| CSS Tutorial/Ref. at W3 Schools | |
| PHP | |
| PHP Tutorial/Ref. at W3 Schools |
If you like my work and/or this has helped you in some way then feel free to help me out for a couple of ☕'s or 🍕 slices!
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This project is a community project not for commercial use.
This project is in no way affiliated with, authorized, maintained, sponsored or endorsed by Raspberry Pi (Trading) Ltd. or any of its affiliates or subsidiaries.
Likewise, This project is in no way affiliated with, authorized, maintained, sponsored or endorsed by Parallax Inc., dba Parallax Semiconductor or any of its affiliates or subsidiaries.
Licensed under the MIT License.
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