Piccolo OS, a Small Multitasking OS for the Raspberry Pi Pico

https://github.com/garyexplains/piccolo_os_v1

by todsacerdoti • 2 years ago

208 51 2 years ago

bsimpson2• 2 years ago

Since the Internet seems to be full of people with way too much time on their hands, I would just like to kindly shoo away any C/C++ pedants out there. Yes, I am sure there are a million different ways to achieve many of the same results. Yes, I am sure there are some fine points of language semantics that could be argued about. Yes, I am sure you have a more efficient way of writing some of the functions.
To be honest, I am not interested.

I respect this so much.

andai• 2 years ago

Piccolo OS [...] is designed primarily as a teaching tool.

This means you must carefully balance teaching the right thing (a realistic system implemented skillfully) against teaching the right way (simplification for didactic purposes).

KerrAvon2• 2 years ago

You shouldn't. This is what hardware people always say, and then when the result is an unmaintainable mess, they want software people to bail them out.

KerrAvon2• 2 years ago

that said, there's not really a lot here, so I'm not sure what anyone would take issue with

bsimpson2• 2 years ago

It's a totally fine and respectable boundary to have: "I'm going to share some stuff I did for free for other people to learn from, but not if I get a bunch of bitchy/pedantic notifications about it."

tredre3• 2 years ago

I respect this so much.

You really shouldn't, Gary is extremely pedantic himself. He really really dislikes criticism or being corrected. For example on youtube, in many of his video comment's, he's engaged in long fights with anyone who claims that Arduino code is C++. In his mind it isn't, therefore that's that.

ladyanita22• 2 years ago

I have found him to say some incorrect stuff and being extremely reluctant to even reflect on it.

I dislike him quite a lot to be honest...

nine_k• 2 years ago

In short: it's a toy OS built primarily for teaching, and it's a cooperative multitasking OS, without process isolation. So it's more like Node.js (or win16, or macOS classic) than like what we usually call an OS.

abelsson• 2 years ago

It’s also running on a microcontroller with a few hundred kb of memory so even win16 or macOS classic would be a bit heavy.

Someone• 2 years ago

so even win16 or macOS classic would be a bit heavy.

Speed-wise, both would run exceptionally well on that hardware.

The first Mac had 128kB memory, about 32 of which were taken by its video and audio buffers. It ran at about 8MHz.

The first version of Windows ran on similar hardware, requiring a 8088 and 256kB of memory.

The pico has at least that amount of memory, at top speed 16 times the clock frequency, and two cores.

rvense3• 2 years ago

The Pico doesn't have an external memory bus, but something like MacOS Classic for an STM32 with a chunk of SDRAM and VGAish video would be fun.

vardump• 2 years ago

Not everything needs to run directly from RAM.

kergonath3• 2 years ago

That’s a weird comment. Node.js is a stack that works on top of an OS. If you could just plop it on a SD card and boot a computer with it, it would be a OS. Things like DOS or MacOS 9 were definitely operating systems. There is no reason to restrict the term to those with preemptive multitasking.

TickleSteve3• 2 years ago

"OS" in this context means "scheduler", i.e the code that coordinates your application tasks. That description can also apply to VMs such as JS, hence the comparison.

You could consider this type of library OS even more tightly bound to the application than your typical JS app as its actually linked to the user code.

whobre• 2 years ago

By your definition, CP/M and DOS are not operating systems either

benj111• 2 years ago

I don't think that makes the definition wrong.

We like to conceptualise OSes as programs, but at the low end they start to resemble libraries.

if your FS is just a library, process switching is timers and interrupts, and memory protection is provided by the processor, what is the OS? Where is the OS?

jollerina• 2 years ago

  struct {
    // ...
  } typedef piccolo_os_internals_t;

  int typedef Int; // also works.

You always learn some new quirk of C. I guess typedef works like const, can put it on the left or the right.

formerly_proven• 2 years ago

TIL and looked it up, typedef is indeed just a specifier like any other in a declaration.

extraduder_ire• 2 years ago

Aren't those the same thing? <type> typedef <name>

My c is pretty rusty, admittedly.

akovaski• 2 years ago

The interesting thing being pointed out is that you can do both `typedef <type> <name>;` (the common way, I think) and `<type> typedef <name>;`.

dariosalvi78• 2 years ago

for a less toy example, it seems like FreeRTOS can be used also on the Rpi pico: https://freertos.org/Documentation/02-Kernel/03-Supported-de...

pkphilip• 2 years ago

This is cool! works well as a way of understanding how to get an OS going on Pico

rbanffy2• 2 years ago

I remember Linux (and NetBSD) running on outrageously low-end hardware (even hardware without an MMU). While modern Linux is a no-go, would there any existing and relatively popular OS be viable?

hackernudes• 2 years ago

You can run modern Linux without an MMU! But other popular embedded OSes I've heard about are FreeRTOS and Zephyr.

jsheard• 2 years ago

And someone has in fact managed to get MMU-less Linux running on the newer Pico 2:

https://github.com/Mr-Bossman/pi-pico2-linux

That's with an 8MB external PSRAM though, fitting modern Linux in the internal SRAM is probably a step too far.

joezydeco• 2 years ago

I used to work with a Cortex-M3 port of uCLinux, but it was kind of a pain to manage. The biggest problem being every executable had to be statically linked to all of its dependencies.

crest4• 2 years ago

You can run uC Linux without an MMU, but you won't get memory safety. Better microcontrollers (that includes the RP2040 and RP2350) have an MPU (memory protection unit) to implement memory safety, but almost no microcontroller has a real MMU (only the MIPS derived PIC32 come to mind). An MPU is far more visibly exposed to the programmer than a paging MMU that combines access control with address space virtualisation. To make it even more annoying the ARMv6M architecture isn't intended to recover from memory usage faults. You have to use really dirty tricks to "fake it" (return from the hard fault into an unimplemented exception, infer the address and cause the fault before you can recover), but it's possible. It's not even that slow. Depending on your usecase a fast warm-start of the whole chip may be preferable to restarting single tasks (e.g. just set the hardware watchdog countdown timer to 1 and spin until it happens).

cmrdporcupine• 2 years ago

Guess it depends on your definition of popular. There's various RTOS products, some of which have POSIX APIs.

If you're fine with obscure and retro, there's things like RISC-OS (ARM). Or EmuTOS (68k/ColdFire). Or FreeDOS etc (x86)

rbanffy2• 2 years ago

I wouldn’t say RISC-OS or EmuTOS would be sensible options for new development unless the point is to develop for them (I wrote a couple programs to use Tektronix 4014 graphics the other day in order to use Tektronix 4014 graphics). I was thinking about reusing existing OSs and their stacks.

jacobmarble• 2 years ago

I've been using protothreads on the RP2040 (Pico MCU) for task management.

https://dunkels.com/adam/pt/

The extensions available from Hunter Adams at Cornell are also very useful. In particular, PT_YIELD_INTERVAL() has been very useful for me.

https://people.ece.cornell.edu/land/courses/ece4760/RP2040/C...

fsiefken• 2 years ago

Fuzix works as well... https://www.reddit.com/r/raspberrypipico/comments/15si3ow/fu...

childintime• 2 years ago

It would be interesting to run each task (likely in simulation), measure the stack size they need, and pre-allocate. That would alleviate the downside of giving each task a stack a lot.

Worth reminding that lots of tasks don't need their own stack, so detecting (or hinting) that would be extremely worthwhile.

Piccolo OS, a Small Multitasking OS for the Raspberry Pi Pico

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