[PATCH] GSoC: Cache configurations Raspberry Pi 2 support

Wed Aug 5 15:46:55 UTC 2015

In arm/shared/startup/linkcmds.base these barriers are used to add
gaps in the memory layout at link-time to accommodate for the size
requirements of the MMU. xbarrier aligns the executable region,
robarrier aligns the read-only memory, and rwbarrier aligns the
read-write memory.

On Tue, Aug 4, 2015 at 6:23 PM, Rohini Kulkarni <krohini1593 at gmail.com> wrote:
>
>
> 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