[PATCH] GSoC: Cache configurations Raspberry Pi 2 support

[Pavel Pisa]

Hello Rohini and Gedare,

On Friday 24 of July 2015 15:33:03 Gedare Bloom wrote:
> What are the values of bsp_section_bss_begin, and bsp_section_bss_size?
>
> Apparently, the memset is trying to write into the .text (code)
> section, which is a very bad thing to do indeed.
>

Qiao Yang in RPi 1 BSP now works in the similar
area to enable right graphic memory mapping.

So my guess is that there could be problem caused
by used MMU mode granularity, which is is 1 MB so
if RO and RW sections are present in the same 1MB
aligned block ten there can be problem. It depends
which section is filled the first. If data and then
text (RO) the troubles begin. If the order is vice
versa then some part of text can be RW instead of RO,
but it should work and cache should not be a problem.

But I have not dig into this case too much.
Only short glimpse.

One option is to define 1 MB alignment between text
ad data for RPi case. There is quite a lot of memory
when compared to most RTEMS embedded targets to the
waste is not so important.

Best wishes,

              Pavel

On Friday 24 of July 2015 21:55:00 Rohini Kulkarni wrote:
> Hi,
>
> I have attached the report containing outputs of arm-rtems4.11-size and
> arm-rtems4.11-nm -S.
>
> From arm-rtems4.11-nm -S I don't see how memset() is accessing .text
> section. The start and end values for both are not overlapping.
>
> On Fri, Jul 24, 2015 at 7:03 PM, Gedare Bloom <gedare at gwu.edu> wrote:
> > On Fri, Jul 24, 2015 at 3:30 AM, Rohini Kulkarni <krohini1593 at gmail.com>
> >
> > wrote:
> > > On 24 Jul 2015 12:35, "Sebastian Huber" <
> >
> > sebastian.huber at embedded-brains.de>
> >
> > > wrote:
> > >> On 23/07/15 23:24, Rohini Kulkarni wrote:
> > >>> I could finally get back to this issue. I used Pi 1 for debugging,
> > >>> but the reason for this problem will apply to Pi 2 also.
> > >>> With text section set to ARMV7_MMU_CODE_CACHED ( which implies read
> >
> > only)
> >
> > >>> , a data abort exception occurs with memset() inside
> >
> > bsp_start_clear_bss()
> >
> > >>> function. An illegal write access to an address according to me.
> > >>
> > >> Which exception and which address? Something is not working here.
> > >
> > > This is a part of the debugging output. When I used
> >
> > ARMV7_MMU_CODE_CACHED.
> >
> > > (gdb) s
> > > bsp_start_clear_bss ()
> > >     at ../../../../../.././raspberrypi/lib/include/bsp/start.h:126
> > > 126      memset(bsp_section_bss_begin, 0, (size_t)
> > > bsp_section_bss_size);
> >
> > What are the values of bsp_section_bss_begin, and bsp_section_bss_size?
> >
> > Apparently, the memset is trying to write into the .text (code)
> > section, which is a very bad thing to do indeed.
> >
> > > (gdb) s
> > > memset (m=0x1157e0, c=0, n=64176)
> > >     at ../../../../../gcc-4.9.2/newlib/libc/string/memset.c:59
> > > 59    ../../../../../gcc-4.9.2/newlib/libc/string/memset.c: No such
> > > file
> >
> > or
> >
> > > directory.
> > > (gdb) s
> > > 49    in ../../../../../gcc-4.9.2/newlib/libc/string/memset.c
> > > (gdb) s
> > > _ARMV4_Exception_data_abort_default ()
> > >     at
> >
> > ../../../../../../../../rtems-local/rtems/c/src/../../cpukit/score/cpu/ar
> >m/armv4-exception-default.S:71
> >
> > > 71        sub    sp, #MORE_CONTEXT_SIZE
> > >
> > > When I set text section flag to ARMV7_MMU_READ_WRITE, the system starts
> > > successfully.
> > >
> > >> --
> > >> Sebastian Huber, embedded brains GmbH
> > >>
> > >> Address : Dornierstr. 4, D-82178 Puchheim, Germany
> > >> Phone   : +49 89 189 47 41-16
> > >> Fax     : +49 89 189 47 41-09
> > >> E-Mail  : sebastian.huber at embedded-brains.de
> > >> PGP     : Public key available on request.
> > >>
> > >> Diese Nachricht ist keine geschäftliche Mitteilung im Sinne des EHUG.
> > >
> > > _______________________________________________
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