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Date:	Thu, 22 Oct 2009 09:03:05 -0700
From:	David Daney <ddaney@caviumnetworks.com>
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To:	"wilbur.chan" <wilbur512@gmail.com>
CC:	"Kevin D. Kissell" <kevink@paralogos.com>,
	Sergei Shtylyov <sshtylyov@ru.mvista.com>,
	linux-mips@linux-mips.org
Subject: Re: Got trap No.23 when booting mips32 ?
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wilbur.chan wrote:
> 2009/10/22 Kevin D. Kissell <kevink@paralogos.com>:
>> wilbur.chan wrote:
>>> Kernal didn't resgister IRQ 23 when booting. Hmm....the only '23'
>>> number I can find in kernel is in traps.c.
>>>
>>> Why a 23 IRQ was triggered?
>>>
>>>
>> The usual reason would be a failure to correctly initialize an interrupt
>> controller, or the Status.IM mask field.  The kernel complains precisely
>> *because* IRQ 23 wasn't registered, but an interrupt was nevertheless
>> delivered that was decoded as being that IRQ.
>>
>>         Regards,
>>
>>         Kevin K.
>>
> 
> 
> Thanks for your suggestion.
> 
> And I found that , as a matter of  fact , kernel has registered No.23 as a trap.
> 
> In trap_init :
> 
> /*
> 1419          * Only some CPUs have the watch exceptions.
> 1420          */
> 1421         if (cpu_has_watch)
> 1422                 set_except_vector(23, handle_watch);
> 
> 
> So, if a No.23 "signal" happened , kernel should  invoke handle_watch instead.
> 
> 
> But why here kernel complained ? and why kernel entered the IRQ branch
> (do_IRQ) rather than trap branch?
> 

You still don't understand.  You are not getting the watch exception. 
The '23' you see is not at all related to the exception code in the 
C0_cause register.

David Daney