* [U-Boot-Users] Customizing U-boot
2004-09-04 3:58 [U-Boot-Users] Customizing U-boot Roy
@ 2004-09-04 12:27 ` Wolfgang Denk
2004-09-06 4:03 ` T Michael Turney
1 sibling, 0 replies; 4+ messages in thread
From: Wolfgang Denk @ 2004-09-04 12:27 UTC (permalink / raw)
To: u-boot
Dear Roy,
in message <000f01c49233$69cee290$030aa8c0@t> you wrote:
>
> U-boot is made to suport many referense boards, but that the use of that?
No, this is not correct. U-Boot was designed to be ported on _any_
hardware. Actually "reference boards" are only a small fraction of
all supported systems - the majority is custom designs.
> it looks more like small OS than bootloader. It finaly must be customized to
This sounds as if this was a bad thing? I think this is one of
U-Boot's big advantages over other boot loaders: you can configure
just the functionality you need, but this includes a lot of things
and options to select from.
> support some specific design only.
Would you prefer a small, dumb boot loader which does not need to be
configured? Then you're wrong on this list. There are many such dumb
solutions - chose something else.
> But I have some problems with this. Can someone tell boot functions
> sequence? they are highly scattered between c modules.
Just follow the flow of control out of reset. And read the mailing
list archive. Your very question has been answered just yesterday (by
T. Michael Turney).
> it taked very long even to find reset vector. u-boot source is not very
> clear.
Ummmm... Maybe you didn't spend much time yet working with U-Boot?
U-Boot is a BIG project. There is about 800,000 lines of code
(including C, assembler and header files). You don't really expect
that you will dig into this without a certain amount of work, do you?
> why random pars are in assembler and others in C ?
Because some things are easier to implement in Assembler than in C.
And because you need a certain runtime environment for C (like a
writable stack) which may not exist at certain stages of initialization.
> When init.S from /board/walnut405 directory is used?
> seems it is dublicated in /board/walnut405/walnut405.c but now in c
> language.
Please check again. There is no common code (not a single routine
with similar function name or purpose).
> when I dissasembled the compiled image I was unable to find anything from
> init.S
Really? You must have done something wrong, then.
When I check, I can for example easily find the code of the
ext_bus_cntlr_init() function in the U-Boot image:
Proof 1:
-> nm u-boot | grep ext_bus_cntlr_init
fff826e0 T ext_bus_cntlr_init
Proof 2:
-> ppc_4xx-gdb u-boot
GNU gdb Yellow Dog Linux (5.2.1-4b_4)
Copyright 2002 Free Software Foundation, Inc.
GDB is free software, covered by the GNU General Public License, and you are
welcome to change it and/or distribute copies of it under certain conditions.
Type "show copying" to see the conditions.
There is absolutely no warranty for GDB. Type "show warranty" for details.
This GDB was configured as "--host=i386-redhat-linux --target=ppc-linux"...
(gdb) disassemble ext_bus_cntlr_init
Dump of assembler code for function ext_bus_cntlr_init:
0xfff826e0 <ext_bus_cntlr_init>: mflr r4
0xfff826e4 <ext_bus_cntlr_init+4>: bl 0xfff826e8 <ext_bus_cntlr_init+8>
0xfff826e8 <ext_bus_cntlr_init+8>: mflr r3
0xfff826ec <ext_bus_cntlr_init+12>: mtlr r4
0xfff826f0 <ext_bus_cntlr_init+16>: li r4,14
0xfff826f4 <ext_bus_cntlr_init+20>: mtctr r4
0xfff826f8 <ext_bus_cntlr_init+24>: icbt r0,r3
0xfff826fc <ext_bus_cntlr_init+28>: addi r3,r3,32
0xfff82700 <ext_bus_cntlr_init+32>: bdnz+ 0xfff826f8 <ext_bus_cntlr_init+24>
0xfff82704 <ext_bus_cntlr_init+36>: lis r3,0
0xfff82708 <ext_bus_cntlr_init+40>: ori r3,r3,40960
0xfff8270c <ext_bus_cntlr_init+44>: mtctr r3
0xfff82710 <ext_bus_cntlr_init+48>: bdnz- 0xfff82710 <ext_bus_cntlr_init+48>
0xfff82714 <ext_bus_cntlr_init+52>: li r4,16
0xfff82718 <ext_bus_cntlr_init+56>: mtdcr 18,r4
0xfff8271c <ext_bus_cntlr_init+60>: lis r4,-25855
0xfff82720 <ext_bus_cntlr_init+64>: ori r4,r4,21632
0xfff82724 <ext_bus_cntlr_init+68>: mtdcr 19,r4
0xfff82728 <ext_bus_cntlr_init+72>: li r4,0
0xfff8272c <ext_bus_cntlr_init+76>: mtdcr 18,r4
0xfff82730 <ext_bus_cntlr_init+80>: lis r4,-15
0xfff82734 <ext_bus_cntlr_init+84>: ori r4,r4,32768
0xfff82738 <ext_bus_cntlr_init+88>: mtdcr 19,r4
0xfff8273c <ext_bus_cntlr_init+92>: blr
End of assembler dump.
(gdb)
> cpu/start.S does similar stuff and by some reason attempts to intialize some
> unknnown FPGA which is clearly unrelated to cpu at all, and should be moved
You got to learn to read the code. Did you see that this part is
bracketed by a "#ifdef CONFIG_BUBINGA405EP" ? So even if the FPGA is
unknown to you, it may be known and probably important to others.
If this is a good place for this part of code is a different issue.
> basicaly I would like to completely rewrite initialization procedure, and
May I suggest that you try to get a better understanding of the code
and it's design principles first?
> put it all in one source file.
This is most definitely not a good idea.
> probably the best would be to discard all exsisting initialization source
> and write new one.
Please go on and do it. Just make sure that your need code does not
need more resources than the existing one, and - most of all - that
it still works on ALL supported systems.
> but I need boot function sequence for that.
> and point where the low level initialization is finished.
I think if you're going to rewrite everything from scratch you should
not bother about the existing crap.
> I need to make custom initialization for ram ,rom, blink leds on gpio.
> and mainly remove al pnp stuff, like spd. probably no real board will ever
> use spd for sram.
Oops. Seems I've seen a lot of unreal boards then. Seems board
manufaturers don;t know what they are doing.
> also removing everyhing unnesecary is required, flash is not hdd aftreall.
> I need it for linuxAP the board is with single ppc405gp cpu with 1mb flash
> and 8mb ram, uart1 pins, and probably pci interface.
> so I need to fit uboot in something like 16kb or less, but first I need to
> make it run at least.
U-Boot was not designed to run in 16 kB, and not even in 64 kB.
> (that 1mb must fit kernel , rootfs, cfgdata, and bootloader) with 486 type
> cpu it is not big problem
>
> Maybe someone know how much u-boot can be stripped?
I'm afraid you're on the wrong list. U-Boot is not what you are
looking for. There are many simple boot loaders without all the fancy
stuff we appreciate in U-Boot, chose one of those instead.
Best regards,
Wolfgang Denk
--
Software Engineering: Embedded and Realtime Systems, Embedded Linux
Phone: (+49)-8142-4596-87 Fax: (+49)-8142-4596-88 Email: wd at denx.de
By the way, ALL software projects are done by iterative prototyping.
Some companies call their prototypes "releases", that's all.
^ permalink raw reply [flat|nested] 4+ messages in thread
* [U-Boot-Users] Customizing U-boot
2004-09-04 3:58 [U-Boot-Users] Customizing U-boot Roy
2004-09-04 12:27 ` Wolfgang Denk
@ 2004-09-06 4:03 ` T Michael Turney
1 sibling, 0 replies; 4+ messages in thread
From: T Michael Turney @ 2004-09-06 4:03 UTC (permalink / raw)
To: u-boot
-----Original Message-----
From: u-boot-users-admin@lists.sourceforge.net
[mailto:u-boot-users-admin at lists.sourceforge.net]On Behalf Of Roy
Sent: Friday, September 03, 2004 8:58 PM
To: u-boot-users at lists.sourceforge.net
Subject: [U-Boot-Users] Customizing U-boot
U-boot is made to suport many referense boards, but that the use of that?
it looks more like small OS than bootloader. It finaly must be customized to
support some specific design only.
> What would you like to have as a reference when you start writing
> firmware for a new board, especially if it isn't COTS hardware? Do you
> really want to wonder about both the hardware and the firmware you
> are porting? Of course it has to be customized, this is the nature of
> boot firmware, every hardware board that runs firmware is different.
But I have some problems with this. Can someone tell boot functions
sequence? they are highly scattered between c modules.
it taked very long even to find reset vector. u-boot source is not very
clear.
why random pars are in assembler and others in C ?
> If you can't follow the boot sequence from .../cpu/XYZ/start.S,
> you don't have any business trying to port u-boot
When init.S from /board/walnut405 directory is used?
seems it is dublicated in /board/walnut405/walnut405.c but now in c
language.
when I dissasembled the compiled image I was unable to find anything from
init.S
> If you ever work for a commercial company that distributes software
> in the embedded space, you will come to recognize this hierarchy...
>
> CPUA
> BOARD1
> BOARD2
> BOARD3
>
> CPUB
> BOARD99
> BOARD100
> BOARD101
>
>Commercial products, generally, are created and distributed against a
>COTS hardware reference platform. Every 8260 COTS hardware board
>has to do some things during boot that every other 8260 board has to
>do. And it has to do some things that are specific to its own collection
>of hardware pieces. I would expect that most public (non static)
> entry points in a file in cpua/board3 would be found somewhere in
>the cpua/board2 directory.
cpu/start.S does similar stuff and by some reason attempts to intialize some
unknnown FPGA which is clearly unrelated to cpu at all, and should be moved
to board specific module.
> Someone who worked on this particular piece of code before you
> obviously had a different opinion. I'm not pretending to know which
> is correct, but would like to share an anecdote. Once, while having
> supervisory responsibilities, I had a guy working on GUIs, with lots of
> supporting libraries and classes already provided. In deference to some
> praise I offered him once, he replied, "Boss, if you like what I done,
> remember, I only reach these heights because I'm walking on the shoulders
> of the giants who came before me."
basicaly I would like to completely rewrite initialization procedure, and
put it all in one source file.
probably the best would be to discard all exsisting initialization source
and write new one.
> fine, do it. You don't need permission.
but I need boot function sequence for that.
and point where the low level initialization is finished.
> .../cpu/XYZ/start.s
> .../lib_abc/board.c
>.../common/main.c
I need to make custom initialization for ram ,rom, blink leds on gpio.
and mainly remove al pnp stuff, like spd. probably no real board will ever
use spd for sram.
also removing everyhing unnesecary is required, flash is not hdd aftreall.
I need it for linuxAP the board is with single ppc405gp cpu with 1mb flash
and 8mb ram, uart1 pins, and probably pci interface.
so I need to fit uboot in something like 16kb or less, but first I need to
make it run at least.
(that 1mb must fit kernel , rootfs, cfgdata, and bootloader) with 486 type
cpu it is not big problem
Maybe someone know how much u-boot can be stripped?
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^ permalink raw reply [flat|nested] 4+ messages in thread