Re: Cannot call C function in "Simple" boot loader
From: Frank (young726_at_yahoo.com)
Date: 04/26/04
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Date: 26 Apr 2004 01:01:10 -0700
Hello Steve,
Yes, I am still struggling. I got some progress, but slowly. ;*( I
think I have solve the problem between boot loader and linux kernel.
Now I got some problems with the kernel booting up.
Right now my vxworks boot loader can start the simple boot loader and
simple boot loader can take over the control and make some
initialization such as serial port initialization etc. And I did get
the serial output such as
"loaded at xxxx xxxx
relocated to xxxx xxxx
zImage at xxxx xxxx
avail ram xxxx xxxx
Now booting the kernel"
But the system hangs after this output. I check the code and found the
head_4xx.S (I am using 405GP) has been called. But somehow the program
stopped at the following part:
"
/* We now have the lower 16 Meg mapped into TLB entries, and the
caches
* ready to work.
*/
turn_on_mmu:
li r0,MSR_KERNEL
mtspr SRR1,r0
lis r0,start_here@h
ori r0,r0,start_here@l
mtspr SRR0,r0
SYNC
rfi /* enables MMU */
"
I don't quite understand how these code can stop the program. Look
like they are simply calling "start_here" and then restoring PC and
MSR. But I put the break point in start_here and was sure that
start_here hasn't been called. Do you have any clue?
Thanks a lot and look forard to hearing from you.
Frank
Steven Rostedt <rostedt@SPAMgoodmis.org> wrote in message news:<c60qtf$n1r$1@news.mch.sbs.de>...
> Hi Frank,
>
> I see you're still struggling over the PPC board and vxworks boot loader.
>
>
> Frank wrote:
> > I am trying to boot up a monta vista linux kernel with vxworks boot
> > loader. The vxworks boot loader can load the "Simple" boot loader and
> > execute it with no
> > problem. But when relocate.S tried to call the C function
> > decompress_kernel() in misc-simple.c, it was stucked and can't go
> > through. I guess there are some stack setup or something else I didn't
> > do it right. Could you give any advice on what could be the problem
> > during C function calling?
>
> Lots of reasons. Did the relocate work? Is the cache off? If it is not
> then the relocation may only happen in the data cache and the
> instruction cache may not know about it, so that when you jump to the
> code, you go nowhere.
>
>
> >
> > BTW, I found this comment in relocate.S:
> >
> > ===========================================================================
> > /* Move this code somewhere safe. This is max(load + size, end)
> > * BIG ASSUMPTION: Addresses below 0x80000000 are assumed to be
> > * in RAM, and addresses above 0x80000000 are assumed to be in
> > * Flash. The cmpw instruction below does a signed integer
> > * comparison, so when comparing a RAM address to a Flash address
> > * the RAM address will always be greater. This allows the
> > * relocation to work when the load address is in Flash.
> > * r8 == load address
> > */
> > GETSYM(r4, start)
> > GETSYM(r5, end)
> > sub r6,r5,r4
> > add r6,r8,r6 /* r6 == phys(load + size) */
> > ===========================================================================
> >
> > I don't quite understand the assumption, i.e. addresses below
> > 0x80000000 are RAM and above are Flash. Where is this assumption
> > reflected in this Simple boot loader? For the board I am using,
> > addresses below 0xFFE00100 are RAM and addresses above 0xFFEE00100 are
> > Flash. How should I change the code (or Makefile?) according to my
> > hardware spec?
>
> Ignore this unless you have over 2 Gigs of RAM. This is just a easy way
> to determine if the code is in RAM or Flash. Yes the flash is usually
> above the 0xffe00000 region which is over 0x80000000, and unless you
> have more that 2 gigs of RAM or your board maps ram from other than zero
> physical address (both unlikely), then you can assume that this
> assumtion is correct.
>
> -- Steve
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