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

[Alan Cudmore]

The raspberry pi BSP uses the shared arm start.S, so the exception handlers
should be there. I guess without a good debugger there is no way to really
know what is going on.

But I will try to turn off the alignment and see if it works tonight.

Alan



On Wed, May 1, 2013 at 3:29 PM, Joel Sherrill <joel.sherrill at oarcorp.com>wrote:

>  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>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 [rtems-users-bounces at rtems.org] On
>> Behalf Of Alan Cudmore [alan.cudmore at gmail.com]
>> Sent: Wednesday, May 01, 2013 8:12 AM
>> To: Gedare Bloom
>> Cc: 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>> 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>> 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
>> >
>> >
>> >
>> >
>> >
>> >
>> > _______________________________________________
>> > rtems-users mailing list
>>  > rtems-users at rtems.org<mailto:rtems-users at rtems.org>
>> > http://www.rtems.org/mailman/listinfo/rtems-users
>> >
>>
>>
>
>
> --
> 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
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.rtems.org/pipermail/users/attachments/20130501/74e18458/attachment-0001.html>