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Re: Olli working, help?

To: linux-mips@fnet.fr
Subject: Re: Olli working, help?
From: Ralf Baechle <ralf@waldorf-gmbh.de>
Date: Wed, 25 Oct 1995 21:32:19 +0100 (MET)
In-reply-to: <199510252006.VAA11758@newton.soft-n-hard.de> from "Andreas Busse" at Oct 25, 95 09:06:21 pm
Hi,

>  > There is just one problem - some SIMM types return the same type code in
>  > the register.  So you have to try if the RAM really exists by accessing it.
>  > If you try to access non existing RAM you'll get a NMI exception which
>  > transfers control to the boot ROM ...
> 
> Have you tried that? I doubt that it really works this way,
> since neither the hardware nor the BIOS can detect the
> difference between these SIMMs with identical IDs. The only
> way to find out what size of memory is installed is to
> access the last address of the expected memory area, and
> if a write-read-verify cycle fails, fall back to the smaller
> size. If the BIOS would get a NMI during this access, it 
> couldn't determine the size either. Or have I missed something?

Yes, the BIOS recognises the NMI and use it to deciede if it has
just tried out writing to nonexisting RAM.

   Ralf

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