Live programming IoT systems with MsgFlo+Flowhub

Last weekend at FOSDEM I presented in the Internet of Things (IoT) devroom,
showing how one can use MsgFlo with Flowhub to visually live-program devices that talk MQTT.

If the video does not work, try the alternatives here. See also full presentation notes, incl example code.

Background

Since announcing MsgFlo in 2015, it has mostly been used to build scalable backend systems (“cloud”), using AMQP and RabbitMQ. At The Grid we’ve been processing hundred thousands of jobs each week, so that usecase is pretty well tested by now.

However, MsgFlo was designed from the beginning to support multiple messaging systems (including MQTT), as well as other kinds of distributed systems – like a networks of embedded devices working together (one aspect of “IoT”). And in MsgFlo 0.10 this is starting to work pretty nicely.

Visual system architecture

Typical MQTT devices have the topic names hidden in code. Any documentation is typically kept in sync (or not…) by hand.
MsgFlo lets you represent your devices and services as FBP/dataflow “components”, and a system as a connected graph of component instances. Each device periodically sends a discovery message to the broker. This message describing the role name, as well as what ports exists (including the MQTT topic name). This leads to a system architecture which can be visualized easily:

Imaginary solution to a typically Norwegian problem: Avoiding your waterpipes freezing in the winter.

Rewire live system

In most MQTT devices, output is sent directly to the input of another device, by using the same MQTT topic name. This hardcodes the system functionality, reducing encapsulation and reusability.
MsgFlo each device *should* send output and receive inports on topic namespaced to the device.
Connections between devices are handled on the layer above, by the broker/router binding different topics together. With Flowhub, one can change these connections while the system is running.

Change program values on the fly

Changing a parameter or configuration of an embedded device usually requires changing the code and flashing it. This means recompiling and usually being connected to the device over USB. This makes the iteration cycle pretty slow and tedious.
In MsgFlo, devices can (and should!) expose their parameters on MQTT and declare them as inports.
Then they can be changed in Flowhub, the device instantly reflecting the new values.

Great for exploratory coding; quickly trying out different values to find the right one.
Examples are when tweaking animations or game mechanics, as it is near impossible to know up front what feels right.

Add component as adapters

MsgFlo encourages devices to be fairly stupid, focused on a single generally-useful task like providing sensor data, or a way to cause actions in the real world. This lets us define “applications” without touching the individual devices, and adapt the behavior of the system over time.

Imagine we have a device which periodically sends current temperature, as a floating-point number in Celcius unit. And a display device which can display text (for instance a small OLED). To show current temperature, we could wire them directly:

Our display would show something like “22.3333333”. Not very friendly, how does one know what this number means?

Better add a component to do some formatting.

Adding a Python component

Component formatting incoming temperature number to a friendly text string

And then insert it before the display. This will create a new process, and route the data through it.

Our display would now show “Temperature: 22.3 C”

Over time maybe the system grows further

Added another sensor, output now like “Inside 22.2 C Outside: -5.5 C”.

Getting started with MsgFlo

If you have existing “things” that support MQTT, you can start using MsgFlo by either:
1) Modifying the code to also send the discovery message.
2) Use the msgflo-foreign-participant tool to provide discovery without code changes

If you have new things, using one of the MsgFlo libraries is a quick way to support MQTT and MsgFlo. Right now there are libraries for Python, C++11, Node.js, NoFlo and Arduino.

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MicroFlo 0.2.0, visual Arduino programming

Two months after MicroFlo 0.1.0, another important milestone has been reached. This release brings a basic visual programming environment and initial support for all major desktop platforms (Win/OSX/Linux). The project is still very much experimental, but it is now starting to demonstrate potential advantages over traditional Arduino programming.

Official release notes and announcement here.

The start of something visual

The “Hello World” adopted from Arduino, a program that blinks the built-in LED a couple of times per second. Pressing Play (>) uploads the program to the Arduino using MicroFlo.

The IDE shown is NoFlo UI, a visual programming environment which can also be used to program JavaScript for the browser and Node.js using the NoFlo runtime. This project is developed by Henri Bergius and rest of the NoFlo team. For more details about the NoFlo IDE project, check their latest update and follow their Kickstarter project.

Talk

At Piksel 2013 in Bergen, I also presented MicroFlo for the first time, to an audience of mostly new media and experimental sound artists. The talk goes into detail about the motivations behind the project, from the quite practical to the more philosophical considerations. Not my most coherent talk, but it gives some insight.

Link

Next

For the next milestone, MicroFlo 0.3, several things are already planned. Focus is mostly on practical improvements to the system, but I also hope to complete prototype support for “heterogeneous FBP”: Allowing to program systems consisting of both host computer and microcontroller programs in a unified manner using NoFlo+MicroFlo.

I am also planning a MicroFlo workshop at Bitraf some time in December and to demo the project at Maker Faire Oslo.

In the meantime, you can get started with MicroFlo for Arduino by following this tutorial. Feedback and contributions welcomed!

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MicroFlo 0.1.0, and an Arduino powered fridge

Lately I’ve been playing with microcontrollers again; Atmel AVRs with and without Arduino boards. I’ve make a couple of tiny projects myself, helped an artist friend do interactive works and helped to integrated a microcontroller it in an embedded product at work. With Arduino, one does not have to worry about interrupts, registers and custom hardware programmers to get things done using a microcontroller. This has opened the door for many more people that pre-Arduino. But the Arduino language is just a collection of C++ classes and functions, users are still left with telling the microcontroller how to do things; “first do this, then this, then this…”.

I think always having to work on such a a low level limits what people make with Arduino, both in who’s able to use it and what current users are able to achive. So, I created a new experimental project: MicroFlo. It has a couple of goals, the two first being the most important:

People should not need to understand text-based, C style programming to be able to program microcontrollers. But those that do know it should be able to use that knowledge, and be able to mix-and-match it with higher-level paradims within a single program.

It should be possible to verify correctness of a microcontroller program in an automated way, and ideally in a hardware-independent manner.

Inspired by NoFlo, and designed for integration with it, MicroFlo implements Flow-based programming (FBP). In FBP, a program is constructed by connecting a set of independent components. Each component has in-ports and out-ports, and can only communicate with eachother through these. The connections can be defined using programatically, using a declarative text language,  or using a visual editor. 2D/3D artists will recognise this the concept from node compositors like in Blender, sound artists from applications like Reaktor.

Current status: A fridge

I have an old used fridge, by the looks of it made in the GDR some time before I was born. Not long after I got it, the thermostat broke and the cooler would not turn off. Instead of throwing it away and getting a new one, which would be the cool and practical* thing to do, I decided to fix it. Using an Arduino and MicroFlo.
* especially considering that it is several months since it broke…

A fridge is a simple system, something that should be simple for hobbyists to create. So it was a decent first usecase to test the framework on. Principially, such a system looks something like this:

 

The thermostat decides whether to turn the cooler on or off, and the cooler switch realizes this decision. There are many alternative methods of implemening each of these two components. I used a DS1820 digital thermometer IC to read temperature, and a hacked NEXA remote controlled relay for the switch.
All the logic, including temperature threshold is done in software on an Arduino Uno.

The code below for the cooler switch would have been simpler (a oneliner, left as excersise for the reader) if I instead had used a active high relay directly on the mains (illegal if not a certified electrician). Or alternatively reverse-engineered the 433Mhz protocol used.

 

MicroFlo code for the fridge, in the .FBP domain specific language (examples/fridge.fbp)
# Thermostat
timer(Timer) OUT -> TRIGGER thermometer(ReadDallasTemperature)
thermometer() OUT -> IN hysteresis(HysteresisLatch)

# On/Off switch
hysteresis() OUT -> IN switch(BreakBeforeMake)
switch() OUT1 -> IN ia(InvertBoolean) OUT -> IN turnOn(DigitalWrite)
switch() OUT2 -> IN ic(InvertBoolean) OUT -> IN turnOff(DigitalWrite)
# Feedback cycle to switch required for syncronizing break-before-make logic
turnOn() OUT -> IN ib(InvertBoolean) OUT -> MONITOR1 switch()
turnOff() OUT -> IN id(InvertBoolean) OUT -> MONITOR2 switch()

# Config
‘5000’ -> INTERVAL timer() # milliseconds
‘2’ -> LOWTHRESHOLD hysteresis() # Celcius
‘5’ -> HIGHTHRESHOLD hysteresis() # Celcius
‘[“0x28”, “0xAF”, “0x1C”, “0xB2”, “0x04”, “0x00”, “0x00”, “0x33”]’ -> ADDRESS thermometer()
board(ArduinoUno) PIN9 -> PIN thermometer()
board() PIN12 -> PIN turnOff()
board() PIN11 -> PIN turnOn()

Is the above solution nicer than using the Arduino IDE and writing in C++? At the moment maybe not significantly so. But it does prove that this kind of high-level dynamic programming model is feasible to implement also on devices with 2kB RAM and 32kB program memory. And it is a starting point for more interesting exploration.

Next steps

I will continue to experiment with using MicroFlo for new projects, to develop more components and test/validate the architecture and programming model. I also need to read through all of the canonical book on FBP by J. Paul Morrison.

Some bigger things that I want to add include:

  • Ability to introspect the graph running on the device, in particular the packets moving between components.
  • Automated testing (of the framework, individual components and application graphs)  using  JavaScript BDD test frameworks like Mocha or Vows.
  • Ability to change graphs at runtime,  and then persist it to EEPROM so it will be loaded on next reset.

And eventually: Allowing to manipulate and monitor running graphs visually, using the NoFlo development environment. See bug #1.

Curious still? Check out the code, and ask on the FBP mailing list if you have any questions!

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