[U-Boot-Users] RAM vs. ROM version of PPCBoot

[Ken Chou]

Hi,

Why RAM version?
Mostly, the convenience is the main reason.

We use COP/BDM debugger during the development.
It is quicker and easier to use RAM version instead of burning the flash
in every turn of the firmware change.  (Just think that you don't have
FLASH and have only one-time PROM.  This might not be the limitation for
most of us today.  Yet, it might be true in some cases.)

It is natural to have RAM version during the development phase since the
final code is moved out of FLASH and runs fro DRAM.  
The DRAM controller and the other initialization steps are done by
debugger.   There is no reason to hung up on the reset vector and always
start from 0xfff00100.  The PC can be changed by the debugger.

I used this method when I just started learning PPCBoot in the 1.1.6
time.
It is pretty useful since I did not have Ethernet and flash routine
working at that time yet.

Whether the RAM version should be checked into the CVS?
It is up to the maintainer to decide.
It might help some that just started U-Boot and without a good way to
program FLASH in the beginning.

I see there are a few board use "CFG_RAMBOOT" flag.
My guess is that someone did the same thing as I did.
Cut an intermediate RAM version in the beginning and move on to the
FLASH version when the code is stabilized on the custom board.

Ken Chou

> -----Original Message-----
> From: Wolfgang Denk [mailto:wd at denx.de]
> Sent: Tuesday, December 03, 2002 4:55 AM
> To: Stephan Linz
> Cc: Mailing list U-Boot
> Subject: Re: [U-Boot-Users] RAM vs. ROM version of ppcboot
> 
> In message <02120313135706.06014 at pcj86.jena.mazet.de> you wrote:
> >
> >
> > I hope it's right to post questions about PPCBoot at U-Boot mailing
> list. I'm
> 
> Given the fact that PPCBoot has been laid to rest, yes.
> 
> > new at PPCBoot, but know about internals of ARMBoot. So I know the
ROM
> and
> > RAM versions of ARMBoot have to differ.
> 
> Ummm... you don;t need a "RAM version" at all.
> 
> > Now, I plan to download PPCBoot into the RAM of a TQM850L via gdb
and
> run
> > from there. Gdb init the target processor inclusive address decoder.
Can
> I
> > load a ppcboot binary builded from plain tarball into the RAM or
schould
> I
> > swap some configs in include/configs/TQM850L.h ?
> 
> Why would you want to  do  this?  U-Boot  (and  PPCBoot)  is  running
> perfectly  fine  from  flash  on all TQ boards. Why would you want to
> create a "RAM version"? It makes no sense to me.
> 
> As the CPU  starts  executing  code  from  the  boot  device  (CS0  =
> typically  flash)  this is the most natural mode to run PPCBoot, too.
> It was written to expect a CPU coming up from reset, so  don't  force
> it  into  any other environment without a good reason and a very good
> understanding of what you do, and why.
> 
> Since you ask this question, I think you should NOT try doing this.
> 
> 
> 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
> Even historians fail to learn from history -- they repeat the same
> mistakes.
> 	-- John Gill, "Patterns of Force", stardate 2534.7
> 
> 
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