AVR Freaks

Not sure if I can post a question here, but why would someone want an operating system for an AVR, a microcontroller? Could someone here who uses such please explain, as I'd never considered such a thing but would like to understand the motivation.

No, it's not correct. scmRTOS is preempteve OS.

There is actually a port for that in the projects section! But you are correct it is not on the list.

Please correct the definition of the scmRTOS. It is preemptive, not cooperative.

thanks for that list. But can anyone tell me, which one RTOS for AVR that use BASIC programing language? please help me

Thanks for your reply Clawson but i already know that script, its not a real RTOS, its just split the procedure into stacks and make priority for task in order every millisecond.
That i want to know is how to make more than one procedures to work simultaneously.
But really i appreciated for your help, thanks,
Do you have any ideas,links,etc?

This is supposed to be tutorial, but all I can see is a list of links. There should be some tutorial in this forum, which explains what RTOS is, what is thread, preempting, etc.

Thank you. Looks good.

SST is a fully preemptive, prioritized RTOS. I have spent a good deal of time over the decades on embedded software and different RTOS's, both commercial and had-rolled. My current favorite is SST. Very light weight, easy to prove correct. Conceptually simple.

So many of the commercial products seem to have a less than required quality, with defects in systems due to the RTOS - why did I buy one if I have to troubleshoot it? I have grown to believe
smaller + simpler = better. SST fits the bill.

DavePed

ChibiOS from Giovanni de Sirio.

http://chibios.sourceforge.net

There is Abassi also. It's preemptive and super small (like <800 bytes small)...

http://www.code-time.com/avr.html
http://www.code-time.com/portdocs.html

i just looked at the first few links...out of which the 2,3 arent related anymore.

Usefull list , cheers to Clawson...which one do you reckon is the easiest to implement with mega128 ? In your experience,

Thanks

@Kartman how about http://www.femtoos.org/doxy/code... ....femtoOS ?

There's no specific reason....only experiment since I have some task to be done ....it can be done with state machine we talked about last time but...I want to try something else...

 

See #43. For each task you need a stack and task control block (TCB). Since many AVRs don't have much ram, you'd really want to be sure you needed a RTOS. For this class of processor, most apps simply don't need a RTOS. Due to the pricing at the moment, you could use an ARM part with much more ram and performance and not be so concerned with the overhead of an RTOS. Whether or not that would be a wise design decision depends on many factors.

clawson, in my opinion, your point of view is centered on the correct usage of an 8bit microcontroller for doing something. 
Has sense to me, that the normal apps doesn't really needs an real RTOS, but i'm referring on the design of such apps. 
Think about IoT, in this case there are some class of applications that need different level of hardware complexity.
It's difficult to do this kind of project using an approach that doesn't use a RTOS or similar system that offer an abstraction layer between the hardware and the logic of the specific app.
In this case i think that an RTOS simplifies a lot the design phase, although if it consume a lot of resources. The important thing is that the hardware meets the app requirements.

Obviously, nothing is necessary, and one reaches the same thing without using an RTOS, but i think that this way isn't simple for the app designer, if the objective of the app designer is centered on the modelling the software of such app.

 

Kartman, conceptually you are near at my project!
I'm aware on the limit that offer the 8bit microcontrollers, but I think it's fair to use all the functionalities that offer such kinds of microcontrollers.
If i have 4k of ram, why i can't use full ram for an given application? 
I have implemented a priority queue using the heap algorithm. I know that this data structure it's ram consuming, but the priority queue give me some functionalities, so is normal that i have to pay a price to obtain this kind of service, i'm aware about this.
Maybe there aren't application that really justify the use of a RTOS on an 8bit microcontroller, i haven't a right experience to answer to this question.
My doubts are about the design of such applications, that in my opinion became easier if one use an RTOS or another similar system.

 

Does an RTOS mean pre-emptible tasks?  That is, where one task can be suspended in favor of a higher priority task. 

However, the your range is very similar with range cited in this article: http://www.ti.com/lit/wp/spry238/spry238.pdf and obviosly, the author of this article think like you.

What I meant it is mainly reported in paragraph 3 of Article. In this sense, the choice on the use of an RTOS for an 8-bit microcontroller is motivated by the fact that a good software architecture inevitably requires the use of an abstraction layer between the hardware and the software. For me it makes sense to accept a decrease in performance (an RTOS on a microcontroller 8bit) if it takes me a serious advantage for my software architecture.
Simple processes that require the use of time and a certain formalism (eg PID or other control systems), can be executed on a microcontroller 8bit (eg ATmega128 / 256), in these cases the use of an RTOS is not essential but much easier life is at the project level and is at the implementation level. This is what I would say based on my limited experience in embedded systems.

Kartman, I understand your motivations and those of clawson only that I agree in part with you. Let me give an example:

I have a Esc, and I have to design an application to make it work. At the moment, I do not know the hardware on which this application should run. 

It can be an ATtiny, an atmega or.. Well, how I can design this application?
Using oop, I can create two classes that help me to abstract the logic of the ESC and the logic of the hardware. Using the uml formalism, I should do something like this:

please ignore the number and the operator + in the association link, also ignore the Eint type, i'm new to papyrus and at this moment i don't know how hide this symbol and use the standard type.

 

This diagram show an important features that is the abstraction. In this case it is rappresented with the PwmIF interface. In this contex the PwmIF interface work like an HAL, an Hardware Abstraction Layers.

I use it to separate the logic of the ESC from the hardware. If my final hardware is an attiny, i need an another class (es AttinyPwm) that extend the PwmIF, same thing if my hardware is a corterx arm or an atmega microcontroller.

So, in this case if you adopt this design, for this simple application, you need 3 class (the Esc class, the PwmIf and the AttinyPwm for ex) and the main obviosly.

Question, are all this class necessary for make this simple application? Maybe not, but this design meets all requirements of this application and, more important, in this way the software is very portable because you have designed it without know nothing about the hardware. But how about the performance? There is a overhead due this design. This is true, but i'm aware of this overhead and i accept it because it is a price that i pay to meets the requirements.

This is that i mean when i express my opinion on the use of a RTOS on an 8bit microcontroller. I prefer to pay something in term of performance at the expense of a good design.

I don't know if this is a good o bad, maybe someone have some cripticism about it, but it work and the code is pretty to read and mantain.

Obviosly there are some application in which this kind of design doesn't work due the overhead, so you can analyse the application before to suggest any desgin, due to my little experience this is my forma mentis.

In the real wold, there are some other factors (like time to develop, the whims of the customer etc) that actually may negatively affect the choice of a type of design, and should be taken into account.

I'm not have considered this aspect, but maybe i should! :)