Re: [ECOS] Hard-Realtime behaviour

[John Carter <john.carter@tait.co.nz>]

On Mon, 19 Jun 2006, R Vamshi Krishna wrote:

> Now this hard real-time OS would be for use in Safety-Critical Systems. We 
> would port the kernel to MISRA-C later stage but currently we are stuck-up at 
> "hardening" of eCos.

Since currently most of the kernel seems to be C++, that wouldn't be
"port", that would be "rewrite". ie. If MISRA-C for the kernel is a
fixed requirement, you have lost right there.

> This guarantee I understand cannot be given by an RTOS alone. It is the 
> combined guarantee by the application + RTOS. i.e. everything depends on the 
> way the application was developed using the features of an RTOS.

Comment 1: Ecos has met all hard deadline requirements on our app...
Getting our code to behave has been way more problematical than Ecos.

Comment 2: Given a choice of a "harder RTOS" than ecos, "misra-c"
kernel, or a faster / smarter CPU with loads of Flash/RAM, I will take
the faster smarter CPU.

Headroom and flexibility are more important than "guarantees".
Guarantees can be broken, but headroom lets you cope with any broken
guarantees and a lot more besides.

Comment 3: Most "hard to meet hard deadlines" I have seen have been the result of
hardware designers saying "lets skimp a bit and fix it in the software".

So if you have a really hard hard to meet RT deadline, walk over to your
hardware designers and talk to them about life, the universe, safety and
trade offs.




John Carter                             Phone : (64)(3) 358 6639
Tait Electronics                        Fax   : (64)(3) 359 4632
PO Box 1645 Christchurch                Email : john.carter@tait.co.nz
New Zealand

Carter's Clarification of Murphy's Law.

"Things only ever go right so that they may go more spectacularly wrong later."

From this principle, all of life and physics may be deduced.

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