At the risk of prolonging a dieing thread I'm going to add my two cents work as I think I have a slightly different perspective. For the record I now 100% agree with Wolfgang it makes no sense to create a new version of U-Boot linked at a different address.
BUT...
When I first started down this path I would have fought tooth and nail for the other approach. I come from an embedded 8/16-bit world where your code runs from ROM of some description and RAM is a very limited commodity. (For instance some of the projects I worked on have only 64-bytes of RAM including register space and stack.) My first though when I started working on PowerPC micro-controllers with a BDM was to use the BDM to initialise the system and then load the code into RAM and debug from there. What a luxury having any kind of debugger that let you step through your code. I created a couple of test applications this way some of which are still used today in our factory to debug the hardware. I even created a RAM only version of PPCBoot that would let me debug PPCBoot it became apparent very quickly that this was causing me a great deal of grief while trying to get PPCBoot working. I created a ROM version of PPCBoot and all of a sudden everything started to work. There are a great many things you are going to have to take out of PPCBoot to get it to work correctly in a RAM only mode. Being able to use RAM to debug from the outset looks like a good idea until you get past taking your first baby steps with PowerPCs but having a minimal BDI script and letting U-Boot do all the rest is a very good idea you will discover this for yourself.
I strongly suggest you listen to guys like Wolfgang he has been there and done it more times than most of the rest of us I suspect. Like me I suspect by the time you have your board working correctly you are going to owe Wolfgang a beer or to good luck.
Regards, Rod Boyce
-----Original Message----- From: Chris Hallinan [mailto:clh@net1plus.com] Sent: Tuesday, December 03, 2002 1:32 PM To: wd@denx.de Cc: u-boot-users@sourceforge.net Subject: RE: [U-Boot-Users] RAM vs. ROM version of PPCBoot
Wolfgang Denk wrote:
In message NEBBKJPFOLJNBMFNKBIIKENKDCAA.clh@net1plus.com you wrote:
Why RAM version? Mostly, the convenience is the main reason.
I can't imaging debugging PPCBoot (or most other flash-resident) code any other way.
Oops? To me it makes absolutely no difference if the code is runing from RAM or ROM. Debugging is exactly the same (OK, you might be limited regarding thenumber of breakpoints when running from ROM, but usually this is no real handicap).
I agree with your comments. The main reason I use RAM version is for load speed.
OK, OK, I just timed it. To erase/program flash using BDI-2000, it takes erase: 3 seconds prog: 6 seconds (with WORKSPACE enabled)
and to load into RAM: load: 2 seconds (with dcache disabled)
So, you're right, the difference isn't really that much! :)
-Chris Hallinan DS4.COM, Inc.
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