[ECOS] Hard-Realtime behaviour

John Carter john.carter@tait.co.nz
Sun Jun 18 23:31:00 GMT 2006


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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