AVR-Chat

Thanks Philippe, but an online document would be more useful to me. A 
simple google search returned this one and I found it interesting, 
AVR related:

http://www.avrfreaks.net/index.php?
module=FreaksArticles&func=downloadArticle&id=14

Behrooz


--- In AVR-Chat@yahoogroups.com, "Philippe Habib" <phabib@...> 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@...
> 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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