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Re: Unknown ARCS message/hang

To: "Erik J. Green" <>
Subject: Re: Unknown ARCS message/hang
From: "Maciej W. Rozycki" <>
Date: Fri, 4 Apr 2003 14:58:02 +0200 (MET DST)
In-reply-to: <>
Organization: Technical University of Gdansk
Original-recipient: rfc822;
On Fri, 4 Apr 2003, Erik J. Green wrote:

> I get the following messages when I try to boot the (very slightly) modified
> linux kernel I am working with:
> --start messages
> Obtaining /vmlinux.64 from server
> 1813568+1150976+172144 entry: 0xa8000000211c4000
> *** PROM write error on cacheline 0x1fcd3b00 at PC=0x211c4018 
> RA=0xffffffff9fc5ace4
> --end messages
> The PC address is the first instruction in head.S (mips64) that touches the
> control register.  I've tried multiple fixes, including initializing the whole
> TLB before the error occurs.  Same error.

 0x211c4018 is a mapped address, which you can't use that early in a boot.

> Can anyone tell me:
> 1) What does this error text mean exactly? 

 An unhandled exception happened due to using a mapped address.  The PROM
caught it and reported. 

> 2) What is "RA"?  The address is a location in the PROM text/stack section.

 It's a CPU register, otherwise known as $31, where the return address is
stored by most of the jump-and-link and branch-and-link instructions.
Here it's an address in the PROM following the "jalr" instruction that
invoked the kernel.

> 3) Am I missing something simple?  An initialization, a rule I'm not 
> following?

 You really want to link your kernel at a KSEG0 address (otherwise you'd
need to struggle with the kernel and the tools to get an unsupported yet
configuration to work).  Basically this means setting LOADADDR in
arch/mips64/Makefile appropriately.  See how it's done for other

+  Maciej W. Rozycki, Technical University of Gdansk, Poland   +
+        e-mail:, PGP key available        +

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