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AW: Some newbie questions


Hi, Andrew,

> -----Ursprungliche Nachricht-----
> Von: Andrew Lunn [mailto:andrew.lunn@ascom.ch]
> Gesendet: Dienstag, 26. Juni 2001 13:55
> An: Andreas Hofer
> Cc: ecos-discuss@sources.redhat.com
> Betreff: Re: [ECOS] Some newbie questions
>
>
> > We have developed a SA1110 based board used to perform CAN bus
> > communication. The CAN controller in use is the Philips
> SJA1000. Some
> > communication partners on the CAN bus expect our board to
> respond within
> > a guaranteed time limit of 40 Microseconds. Guaranteed means hard
> > realtime, right? Can eCos meet these requirements?
>
> eCos is not a hard real time OS. There is no deadline scheduling, no
> guarantees. Everything it best effort. You do have priorities per
> thread, so you can priorities your CAN bus handler above everything
> else to improve is responce time.

But there is no doubt that a thread will be preempted by a interrupt
regardless of its priority, right?

>
> Whats your definition of responce time? The time taken for an ISR to
> run? The time before a thread starts to run? I have an application
> also on an SA1110 processor which requires that the schedular is not
> disabled for longer than 200us. eCos can do that without a problem on
> our target hardware.
>

My definition of response time is the time between receiving a CAN
message from node A and sending back our response to node A. So, within
40us we have to read the CAN message, generate a response message and
send it  back to node A again. Even if the timing would be relaxed to
100 or 200us, we have to guarantee the timeline.

> > How difficult do
> > you expect the adaption of eCos to a new SA1110 based board
> like ours to
> > be?
>
> How different is it to the other SA1110 platforms that are supported?
> Does it use the same flash chips? Same memory layout? etc. The more
> similar it is, the less work involved.
>
>         Andrew
>

Our board has 16Meg of SDRAM and 16Meg of Strata Flash. Porting Linux to
that board was not that much of a pain.

Andreas



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