MBX boot loader on a MPC8260 custom board

MBX boot loader on a MPC8260 custom board

[Julien Eyries]

hi all ,

we have here a custom MPC8260 board (4 Mo flash, 32 Mo SDRAM,200 Mhz
MPC8260) and we want to use the HardHat linux from Montavista.
we are also using BDI-2000 probe (from ABATRON) .

the kernel we have build is based on the ADS8260 board which is quite
similar to our board.

the boot-loader we use is the "mbx" boot loader which come with the
Linux kernel tree.

the problem i have is :
- we load the file "zvmlinux.mbx" using the BDI2000 probe
- we take control over the MPC8260 with "ppc_82xx-gdb zvmlinux.mbx" and
"target remote xx.xx.xx.xx:2001"
- we do some "stepi" and the code runs, entering function
"decompress_kernel", then "serial_init" .
- at some point in this function "serial_init" , the PC (program
counter) begins to count downwards !!! for exemple ( 0x400000 ...
0x3ffffc ... 0x3fff8 ...  )

another point is: when debugging C source code (in emacs + gdb),
we can see that the programms jumps from one point to another (some
times backward) , not following the logical flow of the C source code
.Is that normal ????

what could be the reason of such behaviour ???
does someone here have an idea for our problem ?????


any help is welcome,
greetings,



--
Julien Eyries
R&D engineer
Thales Broadcast & Multimedia (ex-thomcast)
email: julien.eyries@thales-bm.com
fax: 33(0) 1 34 90 31 10
tel: 33(0) 1 34 90 31 01


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Re: MBX boot loader on a MPC8260 custom board

[Wolfgang Denk]

Dear Julien,

in message <3C99BBA3.8090703@thales-bm.com> you wrote:
>
> the kernel we have build is based on the ADS8260 board which is quite
> similar to our board.

Well, is your firmware also similar  to  that  on  the  ADS8260?  The
bootstrap loader provides the interface between firmware and kernel -
so it must match BOTH sides for a given board.

> the boot-loader we use is the "mbx" boot loader which come with the
> Linux kernel tree.

Ummm... did you adap this for your board?

> - at some point in this function "serial_init" , the PC (program
> counter) begins to count downwards !!! for exemple ( 0x400000 ...
> 0x3ffffc ... 0x3fff8 ...  )

This just means you crashed the CPU.

> another point is: when debugging C source code (in emacs + gdb),
> we can see that the programms jumps from one point to another (some
> times backward) , not following the logical flow of the C source code
> .Is that normal ????

With optimized code, yes.  The  compiler  does  several  things  when
optimizing  which  can change the order of the assembler instructions
from what you might expect when reading/writing  C  code.  The  "jump
around" is the consequence.

> what could be the reason of such behaviour ???

Optimization performed by the compiler.

> does someone here have an idea for our problem ?????

Well, my recommendation is to get rid of all this stuff in the mbxbot
directory and use PPCBoot as  firmware  instead;  but  I'm  obviously
biased, and YMMV.

Wolfgang Denk

--
Software Engineering:  Embedded and Realtime Systems,  Embedded Linux
Phone: (+49)-8142-4596-87  Fax: (+49)-8142-4596-88  Email: wd@denx.de
"He was so narrow minded he could see through  a  keyhole  with  both
eyes ..."

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Re: MBX boot loader on a MPC8260 custom board

[Julien Eyries]

Dear Wolfgang,


first let me thank you for your help
we have found the reason for our problem :
it was some specific ADS8260 code which crashe the CPU
on our board . we just had to removed it to have the kernel booting.
even if we see the kernel hanging up a few time latter,
while initializing the FEC , we are now very very happy to see some log
messages from the kernel on the console !!!


>
> Well, my recommendation is to get rid of all this stuff in the mbxbot
> directory and use PPCBoot as  firmware  instead;  but  I'm  obviously
> biased, and YMMV.

Yes  :-) . i had a look at PPCboot which i m sure is very cool ;
and seems to support a lot of commercial boards.

anyway for the moment, it is just O.K. for us if we can do all the
things we have to do, like loading our code via TFTP, debugging and so
on by using our BDI-2000 probe.


Greetings,

Julien.




--
Julien Eyries
R&D engineer
Thales Broadcast & Multimedia (ex-thomcast)
email: julien.eyries@thales-bm.com
fax: 33(0) 1 34 90 31 10
tel: 33(0) 1 34 90 31 01


** Sent via the linuxppc-embedded mail list. See http://lists.linuxppc.org/