[U-Boot-Users] How is the "ba 0xfff80000" located at 0xfffffffc ?

[U-Boot-Users] How is the "ba 0xfff80000" located at 0xfffffffc ?

[腾飞龙]

     As in Embedded Planet EP405 board, ppc405GPr processor support
high boot only, when Power On or reset, the processor starts at
0xfffffffc and the code is executed from flash/rom. There is usually a
branch instruction(such as: ba target) in 0xfffffffc so that it can
jump to the target. For example, if i set TEXT_BASE=0xfff80000 in
u-boot,it means the instruction "ba 0xfff80000" is in 0xfffffffc. My
questions are follow:
  1 where can i find the branch instruction "ba 0xfff80000" in
u-boot-1.1.3 code? it seems it is not in start.s
  2 As we know, before u-boot is written to flash the first time,
there is nothing in flash. when we write u-boot in flash from addr
0xfff80000, how is the branch instruction written to addr 0xfffffffc
which is not neigbour to u-boot code body?
  Thank you and best wishes!

[U-Boot-Users] How is the "ba 0xfff80000" located at 0xfffffffc ?

[Wolfgang Denk]

In message <c002eb610512280133q562c8e91w@mail.gmail.com> you wrote:
>
>   1 where can i find the branch instruction "ba 0xfff80000" in
> u-boot-1.1.3 code? it seems it is not in start.s

As Stefan Roese already pointed out  you  should  NOT  use  old  code
(U-Boot  1.1.3) for any current work. Please use CURRENT code (top of
tree in the git repository), or at least the latest released  version
(1.1.4).

For the code please see cpu/ppc4xx/resetvec.S

>   2 As we know, before u-boot is written to flash the first time,
> there is nothing in flash. when we write u-boot in flash from addr
> 0xfff80000, how is the branch instruction written to addr 0xfffffffc
> which is not neigbour to u-boot code body?

It is part of the U-Boot image. In your case, the binary  image  will
be exactly 512 kB in size, i. e. cover the whole area from 0xFFF80000
to 0xFFFFFFFF.

Best regards,

Wolfgang Denk

-- 
Software Engineering:  Embedded and Realtime Systems,  Embedded Linux
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