[U-Boot-Users] PPC405GP - uboot - can't get past stackloop

Jerry Walden jwalden at digitalatlantic.com
Mon Jan 6 03:37:23 CET 2003

Yes - you are absolutly correct.
Somewhere after about 1000 iterations of placing 0xdeaddead into what is
supposed to be the temporary stack frame, I get a machine exception.

So - now I know my memory is not configured correctly.  My hardware guy is
here, however I see that he has defined 64MB starting at 0x70000000.
However if
I change the value in my config file (CFG_INIT_RAM_ADDR) from 0x4000000 to
I get an immediate fault the first time a store is attempted in that
region - so
r4 has something like 0x70001f48 in it, and I get the fault the very first
I execute the stwu instruction.  However with the BDI, I can change memory
at 0x7000000 - 0x7fffffff all day long without a complaint.  So obviously
code I am running at the very start of start.S is not setting something up
properly.  Question is, what is it?

-----Original Message-----
From: wd at denx.de [mailto:wd at denx.de]
Sent: Sunday, January 05, 2003 3:03 PM
To: jwalden at digitalatlantic.com
Cc: u-boot-users at lists.sourceforge.net
Subject: Re: [U-Boot-Users] PPC405GP - uboot - can't get past stackloop

In message <EGEGIJHKDKJGAJMGIDPNEEAECEAA.jwalden at digitalatlantic.com> you
> 	Now - I start tracing from the _start, and I get to:
> 	..stackloop
> 		stwu	r4, -4(r2)
> 		bdnz	..stackloop

Stop right before "..stackloop" and verify that  the  stack  area  is
really  readable  and  writable, i. e. check if your initial RAM area
(in data cache or OCM ?) is configured correctly and working.

> 	If I set a breakpoint after the bdnz, the debugger never breaks - it is
> though it is in
> 	an infinite loop.

...because the CPU never gets there, because it's taking an exception

> 	If I "interrupt" in DDD, the following message is displayed:
> 	Program received signal SIGSTOP, Stopped(Signal)
> 		0x00000700 in ??()

Right, an exception happened.

> 	Any hint as to what might be going wrong?

Your initial RAM area is configured incorrectly and does not work?

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
We are drowning in information but starved for knowledge.
                                         -- John Naisbitt, Megatrends

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