[PATCH] GSoC: Cache configurations Raspberry Pi 2 support

Tue Aug 4 22:23:43 UTC 2015

On Wed, Aug 5, 2015 at 1:47 AM, Gedare Bloom <gedare at gwu.edu> wrote:

> On Tue, Aug 4, 2015 at 2:18 PM, Rohini Kulkarni <krohini1593 at gmail.com>
> wrote:
> >
> >
> > On Tue, Jul 28, 2015 at 5:51 AM, Pavel Pisa <ppisa4lists at pikron.com>
> wrote:
> >>
> >> 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.
> >
> >
> > I didn't quite get what this means. I have no clue on how to proceed with
> > this.
> The MMU defines memory regions in 1MB chunks. Each chunk can have its
> own permissions (read-only, or read-write) set. If the .text and .data
> (or some other section) overlaps in the same 1MB chunk, and the wrong
> permission gets set, then there can be a problem e.g. part of .data
> might be RO or part of .text might be RW.
>
> Did you try the code Sebastian posted? to change the robarrier to
> rwbarrier?
>

What exactly are these barriers?

>
> Gedare
>
> >>
> >>
> >> 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.
> >> > > >
> >> > > > _______________________________________________
> >> > > > devel mailing list
> >> > > > devel at rtems.org
> >> > > > http://lists.rtems.org/mailman/listinfo/devel
> >>
> >
> >
> >
> > --
> > Rohini Kulkarni
> >
> > _______________________________________________
> > devel mailing list
> > devel at rtems.org
> > http://lists.rtems.org/mailman/listinfo/devel
>

-- 
Rohini Kulkarni
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