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Introducing multitasking to Arduino

blog.arduino.cc

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Re: Introducing multitasking to Arduino

#51

Post by AnonymousPlanet »

gmiller123456 wrote: post #46
xkcd-sucks wrote: post #4

I'm crappy at embedded development but isn't it pretty normal to handle "multitasking" with interrupts instead of using an event loop?

Not really, the processor has to be designed to support it that way to make it practical. With interrupts, execution can be interrupted at any point, and you have to be able to restore the registers to the correct state before letting the process continue from that point. It's technically doable, but with a chip that has only 128 bytes of RAM, you'll be pretty limited in how many processes you can run. Even Windows,…

> Even Windows, prior to Win95, used the event loop style for multitasking.

Even? That's nearly the lowest bar regarding multitasking, compared to other OSes of the time.

Re: Introducing multitasking to Arduino

#52

Post by skybrian »

petsfed wrote: post #45
skybrian wrote: post #20

Earlier quoted context omitted.

It's not quite the same as a while loop, because when you return from the loop() function, how long it takes before it gets called again isn't defined. Using arduino-pico, for example, it does some USB I/O handling (when using TinyUSB). If you write an actual while loop and don't return from the loop function often enough, you might starve the USB port implementation. This adds enough of a delay that I moved some cod…

That's a fair point. I admit, I moved away from the Arduino framework pretty rapidly after embedded development became my job, well before I had to contend with everything else under the hood. I never ran into an issue of quasi-hidden behaviors like that, because I never pushed the thing that hard. It feels a little bit like the Arduino toolset (that is pre IDE 2.0) was designed to discourage people from pushing thin…

Well, it's behavior specific to one board, and perhaps to TinyUSB. But it looks like Arduino has a yield function [1] that you can use to run periodic tasks if you write your own loop. And Teensy calls yield() between calls to loop(). [2]

Since switching to VSCode and PlatformIO, I read the source more. (Arduino 1.x discouraged this due to not having easy ways to navigate between callers and callees.)

[1] https://www.arduino.cc/reference/en/libraries/scheduler/yiel... [2] https://github.com/PaulStoffregen/cores/blob/master/teensy4/...

Re: Introducing multitasking to Arduino

#53

Post by Teknoman117 »

Tajnymag wrote: post #27
ramary wrote: post #25

We've done quite a bit of experimentation with adding preemptive multitasking support to non-hard real time software running on MCUs at my current company. After a lot of head banging and dead ends, I've come to the conclusion personally that the embedded community could really use an implementation of the POSIX threading APIs or some meaningful subset thereof for various platforms. They're already standardized, well…

Threads are already supported by esp-idf on esp32 source: https://docs.espressif.com/projects/esp-idf/en/latest/esp32/...

Do you know how the core scheduling works? Does it migrate tasks between cores? Is there any notable core to core migration penalty?

Re: Introducing multitasking to Arduino

#54

Post by skybrian »

ge96 wrote: post #19
dvh wrote: post #10

Earlier quoted context omitted.

Esp32 boards has 2 cores and cost $5, works fine in Arduino. Try AliExpress.

Showing some Teensy love, crazy the 4.0 has 600MHz base speed.

Teensy is great, but that puts you in the $20 range and doesn't have WiFi.

Re: Introducing multitasking to Arduino

#55

Post by jldugger »

primitivesuave wrote: post #16

A couple years ago, I managed a summer/afterschool program that introduced thousands of kids (age 8-18) to the Arduino. When we would set up a software abstraction to simplify multitasking (something that came up often with more advanced students), we set up something like this: int time = 0; int max_period = 10000; void loop() { if (time % 100 == 0) { everyTenthSecond(); } if (time % 1000 == 0) { everySecond(); } //…

This basically how all of arduino "works". It was quite shocking to see this after working on embedded systems in grad school that used interrupt driven microcontrollers for low power situations to see a while (true) in the core arduino main.c

edit: but it makes sense from the perspective of a education and hobbyist needs to take the simplest option that could work

Re: Introducing multitasking to Arduino

#56

Post by seabird »

Teknoman117 wrote: post #32
gnramires wrote: post #23

Earlier quoted context omitted.

I wonder if it's possible to just interleave statements from k different (loop) functions? Then it would seem mostly equivalent to an arduino at 1/k Clock speed. I think it's not possible to interleave instructions per se (because of registers?), but a compiler should be able to figure out the correct instructions of statement interleaving. This should eliminate problems with blocking.

Anyone know if a barrel-processor microcontroller exists? Propeller is sort of that way at least regarding main memory access.

Padauk makes them (or at least did), and calls them FPPAs. These are the same folks that brought you those infamous 3-cent-at-single-quantities OTP microcontrollers, so they're probably not for the faint of heart, but what you're asking for has been done.

Re: Introducing multitasking to Arduino

#57

Post by HeyLaughingBoy »

botdan wrote: post #47
HeyLaughingBoy wrote: post #26

Earlier quoted context omitted.

> move up to a larger system I'll take this one step further and suggest that beginners not start with the AVR, but instead with a Blue/Black pill (STM32) or ESP32. Leave the AVR for the more advanced people who are trying to squeeze every penny out of a project (even there, in many cases STM32 will cost less!!!). I visit the arduino.cc forums at least once every day and the things that beginners want to do these day…

I'm a casual embedded-electronics user at best, most of my projects haven't advanced much past turn a simple servo, light some LEDs, maybe read a sensor and POST to an endpoint. For these tasks, Arduino has been pretty good for me and removed a lot of the complexity. The `setup()` and `loop()` model makes a lot of intuitive sense. That being said, I've spent no small amount of time on `String` vs `char*` (as an inexp…

The beauty of the Arduino is the ecosystem behind it. The original hardware is verging on obsolescence, to be polite, but the same code and programming methods can be used on STM32 hardware (that's Arduino-compatible, like the Blackpills) or ESP32. The main difference is that now you have much faster, more modern processors, far more Flash and RAM to play with, not to mention a more powerful I/O peripheral structure if you want to dig into it at that level.

FreeRTOS on an ESP32 in the Arduino IDE is effectively free: you don't have to do anything to enable it. It's pulled in by default.

AFAIK, Arduino support for STM32 is limited to the F103 & F4xx series.

I confess that since my entry point is as a professional, I really haven't kept up with what other hobbyist-level entries are still on the market. That said, a good place to start would be with an STM32 Discovery board -- if you can find one these days! Looks like Digi-Key has exactly 1 in stock rn. It's a $19.95 board with an 'F407 and some sensors and output devices. No external tools needed: you can program it through a USB port. All the tools can be downloaded from ST Thomson or its partners for free. This is more entry-level professional than hobbyist, but there's no sharp dividing line there.

The Raspberry Pi pico is also taking off: https://www.raspberrypi.com/products/raspberry-pi-pico/ I haven't used one yet, but they seem to be amazing little devices and the community is rallying around them.

Re: Introducing multitasking to Arduino

#58

Post by flyingcircus3 »

botdan wrote: post #47
HeyLaughingBoy wrote: post #26

Earlier quoted context omitted.

> move up to a larger system I'll take this one step further and suggest that beginners not start with the AVR, but instead with a Blue/Black pill (STM32) or ESP32. Leave the AVR for the more advanced people who are trying to squeeze every penny out of a project (even there, in many cases STM32 will cost less!!!). I visit the arduino.cc forums at least once every day and the things that beginners want to do these day…

I'm a casual embedded-electronics user at best, most of my projects haven't advanced much past turn a simple servo, light some LEDs, maybe read a sensor and POST to an endpoint. For these tasks, Arduino has been pretty good for me and removed a lot of the complexity. The `setup()` and `loop()` model makes a lot of intuitive sense. That being said, I've spent no small amount of time on `String` vs `char*` (as an inexp…

I think AVR is a good architecture to learn on, because the devices are far simpler than ARM or other more modern chips. The main concept to master as an embedded developer is operating a device by its registers. The common arduino device, ATMEGA328, has a total of 84 registers across all peripherals. A simple program to blink the LED is less than 10 lines total. The datasheet is tiny compared to most ARM devices, but is still a complete source of information.

There are lots of libraries online that demonstrate how to set up registers for various peripherals. Avrgcc is an open source toolchain, and avrdude can program devices running the arduino bootloader.

Re: Introducing multitasking to Arduino

#59

Post by seabird »

atoav wrote: post #8
HeyLaughingBoy wrote: post #3

Nice, but pointless addition to an old processor. ESP32's are cheap and readily accessible and they come with FreeRTOS running already. If I absolutely need to multitask on a Mega328 Arduino, I use the protothreads library. But really, for anything heavy, I'll turn to an ESP32 or an STM32. Use the right tool for the job!

Yeah, the art students with miniscule coding experience who just want to get stuff done are probably going to be thrilled to work with FreeRTOS. The truth is, that Arduino always has put in a lot of work to do things that could already be done only to make them more accessible, easier to use and thus more widely available. If you think this is pointless you should consider this might say more about how far you have c…

The art students with minimal coding experience would take FreeRTOS ten times out of ten over trying to figure out what a compare match timer is, what an interrupt is, how bitwise operations work, etc. The OP was dead-on and I'd bet money that the downvotes are from people that have never had somebody's eyes glaze over when they told them that they "just need to calculate their prescaler values, mask the appropriate bits into the config register, set the number of counts in the compare register, enable the timer interrupt, and register an interrupt vector to handle it".

Re: Introducing multitasking to Arduino

#60

Post by NavinF »

gnramires wrote: post #23
primitivesuave wrote: post #16

A couple years ago, I managed a summer/afterschool program that introduced thousands of kids (age 8-18) to the Arduino. When we would set up a software abstraction to simplify multitasking (something that came up often with more advanced students), we set up something like this: int time = 0; int max_period = 10000; void loop() { if (time % 100 == 0) { everyTenthSecond(); } if (time % 1000 == 0) { everySecond(); } //…

I wonder if it's possible to just interleave statements from k different (loop) functions? Then it would seem mostly equivalent to an arduino at 1/k Clock speed. I think it's not possible to interleave instructions per se (because of registers?), but a compiler should be able to figure out the correct instructions of statement interleaving. This should eliminate problems with blocking.

You can do that, but it's not very useful in practice and really breaks down when you want to do something more compute intensive that needs all the registers/cache. Multicore MCUs like the ESP32 are pretty cheap ($2 1pc pricing) so if you really care about realtime performance it makes more sense it do realtime on one core and schedule slower work to be done on the other core.
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