[prev in list] [next in list] [prev in thread] [next in thread] 

List:       linux-arm-kernel
Subject:    Re: Problem with FIQ on at91rm9200
From:       "Jean-Philippe Francois" <jp.francois () cynove ! com>
Date:       2004-05-19 8:33:31
Message-ID: 200405191033310109.0032E646 () smtp ! wanadoo ! fr
[Download RAW message or body]



it was "bad mode in data abort handler". The interesting thing is that the 
> CPU is only in ABT_32 for a very short time within the data abort handler, 
> just before it switches to SVC_32. So unless you generate a data or
> prefetch 
> abort in ABT_32 its impossible be in a bad mode there.
> 
> Aborts have a higher priority than normal IRQs and the CPU disables IRQs
> when 
> executing an abort. So unless you enable IRQs before switching to SVC
> mode, 
> there should be no way for an IRQ to happen while you're in ABT_32. 

Agreed, but I am not touching any CPSR or SPSR register in my routine, except when \
doing the usual pc restore.

> Unless 
> you make an error when restoring the CPSR from the SPSR and restore into 
> ABT_32 with interrupts enabled ;-)
> 
> But I guess you're not tinkering with the processor modes while executing
> the 
> FIQ.
> 
> There's one special thing about FIQ and ABT however: If FIQ and ABT happen
> "at 
> the same time", the CPU first takes the ABT and then the FIQ immediately 
> afterwards. So you're then in FIQ mode with the SPSR from ABT. Still, this 
> should be absolutely safe unless you make wrong assumptions about SPSR
> being 
> always SVC or USR and restore into the wrong mode.
> 

So you have something like this :

User -> ABT32 : spsr = cpsr_usr cpsr=cpsr_abt32
ABT32 -> FIQ : spsr = cpsr_abt32

Then subs pc,lr,#4 restore the cpsr_abt32 right ?

I would understand a bad mod in data abort : FIQ 32.

But I am still looking for what could cause a bad mode in interrupt handler.


> regards,
> 	matthias
> 

Thank you,

JP Francois


-------------------------------------------------------------------
Subscription options: http://lists.arm.linux.org.uk/mailman/listinfo/linux-arm-kernel
FAQ:       http://www.arm.linux.org.uk/armlinux/mlfaq.php
Etiquette: http://www.arm.linux.org.uk/armlinux/mletiquette.php


[prev in list] [next in list] [prev in thread] [next in thread]