ARM alignment MMU setting again was Re: Raspberry Pi BSP debugging

[Joel Sherrill]

On 5/1/2013 2:25 PM, Alan Cudmore wrote:
> It looks like the CP15 initialization is explicitly enabling unaligned 
> traps, so that is the likely cause.
This came up recently (past week?). The default setting with the
MMU initialization code makes it a fault.

Unless we compile newlib and other tool libraries to have strict
alignment, unaligned access must be allowed.  My gut says
cp15 is setup wrong by default for the way we generate code.

Gedare has mentored the MMU projects so let's bring him in.
> The BSP has a good polled printk, so I might try to setup something 
> for the exception vectors as well.
I wonder why there isn't a good exception handler. :(

Is there not one? Or did you just not get that part of the
ARM BSP shared setup?

> Thanks,
> Alan
>
>
>
> On Wed, May 1, 2013 at 1:11 PM, Claus, Ric <claus at slac.stanford.edu 
> <mailto:claus at slac.stanford.edu>> wrote:
>
>     It's not clear what your debugging environment is like, but if you
>     could put some sort of indicator (e.g. a printk, a write to memory
>     that is persistent across reboots, or turn on an LED) in each of
>     the exception vectors (except IRQ, since it will be tickled often
>     by at least clock), then you could tell whether you've taken an
>     exception.  It smells like you're taking an alignment exception
>     and landing in a for (;;) loop.
>
>     It'd interesting to know the pros and cons of enabling unaligned
>     accesses with CP15.  Naively, it might seem like a good idea to
>     always enable these.  Presumably it kills performance to do so,
>     however.
>
>     Ric
>
>     ________________________________________
>     From: rtems-users-bounces at rtems.org
>     <mailto:rtems-users-bounces at rtems.org>
>     [rtems-users-bounces at rtems.org
>     <mailto:rtems-users-bounces at rtems.org>] On Behalf Of Alan Cudmore
>     [alan.cudmore at gmail.com <mailto:alan.cudmore at gmail.com>]
>     Sent: Wednesday, May 01, 2013 8:12 AM
>     To: Gedare Bloom
>     Cc: rtems-users at rtems.org <mailto:rtems-users at rtems.org>
>     Subject: Re: Raspberry Pi BSP debugging
>
>     Great idea. It should be easy enough to try, and it looks like the
>     bit to enable unaligned access is not set in the BSP.
>
>     Thanks,
>     Alan
>
>
>
>     On Wed, May 1, 2013 at 10:38 AM, Gedare Bloom <gedare at rtems.org
>     <mailto:gedare at rtems.org><mailto:gedare at rtems.org
>     <mailto:gedare at rtems.org>>> wrote:
>     Could it be a matter of the compiler (not) knowing the correct
>     alignment for the target architecture?
>
>     To quote Sebastian from a recent post: "Please have a look in the
>     ARM1176JZF-S manual.  You may have to enable the unaligned access in
>     the CP15."
>
>     -Gedare
>
>     On Wed, May 1, 2013 at 10:16 AM, Alan Cudmore
>     <alan.cudmore at gmail.com
>     <mailto:alan.cudmore at gmail.com><mailto:alan.cudmore at gmail.com
>     <mailto:alan.cudmore at gmail.com>>> wrote:
>     > I'm trying to track down a bug in the Raspberry Pi BSP. It will
>     be much
>     > easier once I get a JTAG device, but for now I have been able to
>     narrow down
>     > one specific instance where the BSP hangs.
>     >
>     > The first symptom of this problem was with a shell example. If I
>     type an
>     > invalid shell command, I noticed it will hang or crash on the
>     strncat
>     > function.
>     >
>     > Next, I modified the simple hello world sample and found that it
>     will also
>     > hang with a strncat call. I copied the strncat function from the
>     newlib
>     > sources and found that the local copies ( optimized for size and
>     speed )
>     > work. The attached example shows the two local strncat calls
>     followed by the
>     > newlib call. It will always hang on the newlib call.
>     >
>     > This example works on the arm920/gdb simulator and the sparc-sis
>     simulator.
>     >
>     > Some other notes;
>     > - The memory map looks reasonable, comparing it to the arm920 map
>     > - Many other newlib functions work such as strncpy, printf, etc
>     > - Much of the other basic RTEMS seem to work as well. I can
>     create a RAM
>     > disk, format it , mount it, copy files, etc. I ran many of the
>     tests such as
>     > unlimited, ticker, etc.
>     >
>     > If anyone has an idea I can try let me know. Otherwise I might
>     just wait
>     > until I can get a JTAG device hooked up.
>     >
>     > Thanks,
>     > Alan
>     >
>     >
>     >
>     >
>     >
>     >
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>     >
>
>


-- 
Joel Sherrill, Ph.D.             Director of Research & Development
joel.sherrill at OARcorp.com        On-Line Applications Research
Ask me about RTEMS: a free RTOS  Huntsville AL 35805
Support Available                (256) 722-9985

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