AVR-Chat

Could you do that Philippe?  There have been a couple of questions about 
multitasking and RTOS systems in the past little bit and that might help 
those who are coming to terms with uses for these...where to use them 
and where not.

Thanks,

REB


Philippe Habib wrote:

>I have a book that does a great job of explaining this, but its at home.  If
>there is interest I can dig up the title.  I used it as the textbook for an
>embedded programming course I took years ago.
>
>-----Original Message-----
>From: AVR-Chat@yahoogroups.com [mailto:AVR-Chat@yahoogroups.com] On Behalf
>Of subscriptions@aeolusdevelopment.com
>Sent: Tuesday, January 22, 2008 9:27 AM
>To: avr-chat@yahoogroups.com
>Subject: Re: [AVR-Chat] Re: WinAvr or CodeVision, which one is more public?
>
>David VanHorn Wrote
>  
>
>>>U talked of RTOS. Never heared of it before, but my MCU needed to
>>>control RH, light level and temperature real time and show them on
>>>LCD, so I thought and then I made for myself a sort of virtual multi-
>>>tasking procedure, for example:
>>>
>>>Do
>>> Gosub v
>>> Gosub w
>>> Gosub x
>>> Gosub y
>>> Gosub z
>>>Loop
>>>End
>>>
>>>      
>>>
>>This is the guts of a cooperative multitasker.
>>    
>>
>
>A simple co-operative multitasker.  This particular kind is often referred
>to as a super loop and is simple enough that some object to it being
>referred to as a multitasker.  They prefer to think of it as a single task
>state machine.  There is a grey area here.
>
>Time for a little RTOS taxonomy I think
>
>RTOS's can be classified as
>
>   pre-emptive or co-operative
>   single stack (run to completion) or multiple stack
>   round-robin or priority
>
>There are other characteristics but I think these are the most important
>and these characteristics are independent.  Independence does not mean you
>can change just one item in any particular implementation just that you can
>implement any combination.
>
>The above is a co-operative, round-robin, single stack multitasker.
>
>pre-emptive systems bring in the ability to interrupt the current task at
>any time but also need to be able to protect critical sections from being
>interrupted by other tasks.  Co-operative systems generally remove the need
>to implement as many safeguards but their responsiveness and the
>granularity of tasks falls completely on the programmers shoulder showing
>up in the task breakdown itself.
>
>Single stack systems use only a single stack (obviously) and thus have
>simpler memory management and task switching.  Multiple stacks allow tasks
>to block waiting for resources or data.
>
>Round-robin provides simple fairness.  Priority based allows more frequent
>and/or more important tasks first access improving responsiveness if done
>correctly.
>
>Other characteristics include types of IPC, memory allocation, device
>driver model (if any), task creation ....
>
>Robert
>
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