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Re: Strange, strange occurence

To: S C <theansweriz42@hotmail.com>
Subject: Re: Strange, strange occurence
From: Ralf Baechle <ralf@linux-mips.org>
Date: Sat, 10 Jul 2004 12:04:12 +0200
Cc: linux-mips@linux-mips.org
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On Fri, Jul 09, 2004 at 06:50:00PM +0000, S C wrote:

> Using MontaVista Linux 3.1 on a Toshiba RBTx4938 board. Using YAMON, when I 
> download the kernel via the debug ethernet port it runs fine. If I download 
> the kernel via the Tx4938 inbuilt ethernet controller, it crashes!

If you're using a Montavista kernel you should report to Montavista.  We
don't have the source so any comment here is speculation.

> The crash is occuring inside the function r4k_flush_icache_range().
> 
> I tried 'flush -i' and 'flush -d' on YAMON after the download but before 
> the 'go', but that didn't help. I also tried completely disabling caches 
> and loading/running uncached, but it gave the same error.
> 
> Now, the final twist! Using an ICE, I set a breakpoint at the 
> r4k_flush_icache_range function. Then I loaded the kernel as usual, ran it 
> with the ICE, stepped through a few instructions inside the 
> r4k_flush_icache_range function and then did a 'cont'. The kernel now 
> booted fine!

As already pointed out by the other poster Niels Sterrenburg using a
debugger unavoidably changes the state of the system to be debugged.

For at least some of the TX49xx processors there is a problem under certain
circumstances if a flush of an I-cache line flushes that cache instruction
itself.  Make sure you're not getting hit by that one.

  Ralf

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