[PATCH] GSoC: Cache configurations Raspberry Pi 2 support

Tue Aug 4 20:17:45 UTC 2015

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?

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.
>> > > >
>> > > > _______________________________________________
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>> > > > devel at rtems.org
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>>
>
>
>
> --
> Rohini Kulkarni
>
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