* RFI instruction not working as expected...
@ 2007-03-15 5:52 Siva Prasad
2007-03-15 11:50 ` Jerry Van Baren
0 siblings, 1 reply; 3+ messages in thread
From: Siva Prasad @ 2007-03-15 5:52 UTC (permalink / raw)
To: linuxppc-dev
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Hi,
I am trying to boot my 8641D based PowerPC board. I am having trouble
booting it.
Following code snippet is from head_32.S.....
lis r4,2f@h
ori r4,r4,2f@l
tophys(r4,r4)
li r3,MSR_KERNEL & ~(MSR_IR|MSR_DR)
FIX_SRR1(r3,r5)
mtspr SPRN_SRR0,r4
mtspr SPRN_SRR1,r3
SYNC
RFI
/* Load up the kernel context */
2: bl load_up_mmu
My code successfully reaches up to the RFI instruction, but never to "2:
bl load_up_mmu". I am not using any debugger (used an LED write to
address to figure it out) in this situation.
Any suggestions on why my execution sequence never reaches the "2: "?
I exhausted all types of debug information and appreciate any help.
Thanks
Siva
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* RFI instruction not working as expected...
@ 2007-03-15 5:53 Siva Prasad
0 siblings, 0 replies; 3+ messages in thread
From: Siva Prasad @ 2007-03-15 5:53 UTC (permalink / raw)
To: linuxppc-embedded
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Hi,
I am trying to boot my 8641D based PowerPC board. I am having trouble
booting it.
Following code snippet is from head_32.S.....
lis r4,2f@h
ori r4,r4,2f@l
tophys(r4,r4)
li r3,MSR_KERNEL & ~(MSR_IR|MSR_DR)
FIX_SRR1(r3,r5)
mtspr SPRN_SRR0,r4
mtspr SPRN_SRR1,r3
SYNC
RFI
/* Load up the kernel context */
2: bl load_up_mmu
My code successfully reaches up to the RFI instruction, but never to "2:
bl load_up_mmu". I am not using any debugger (used an LED write to
address to figure it out) in this situation.
Any suggestions on why my execution sequence never reaches the "2: "?
Appreciate any help.
Thanks
Siva
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^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: RFI instruction not working as expected...
2007-03-15 5:52 RFI instruction not working as expected Siva Prasad
@ 2007-03-15 11:50 ` Jerry Van Baren
0 siblings, 0 replies; 3+ messages in thread
From: Jerry Van Baren @ 2007-03-15 11:50 UTC (permalink / raw)
To: Siva Prasad; +Cc: linuxppc-dev
Siva Prasad wrote:
> Hi,
>
> I am trying to boot my 8641D based PowerPC board. I am having trouble
> booting it.
>
> Following code snippet is from /head_32.S/…..
>
> lis r4,2f@h
> ori r4,r4,2f@l
> tophys(r4,r4)
> li r3,MSR_KERNEL & ~(MSR_IR|MSR_DR)
> FIX_SRR1(r3,r5)
> mtspr SPRN_SRR0,r4
> mtspr SPRN_SRR1,r3
> SYNC
> RFI
> /* Load up the kernel context */
> 2: bl load_up_mmu
>
> My code successfully reaches up to the RFI instruction, but never to
> “*/2: bl load_up_mmu/*”. I am not using any debugger (used an LED write
> to address to figure it out) in this situation.
>
> Any suggestions on why my execution sequence never reaches the “*/2:/* “?
>
> I exhausted all types of debug information and appreciate any help.
>
> Thanks
> Siva
Please don't post HTML.
If you are debugging with an LED, you really don't know if you are
getting past the RFI or not.
This is the point where the MMU gets enabled and you are transitioning
from physical mapping to MMU-controlled (virtual) mapping. After the
RFI and before the MMU is set up, you have a *VERY MINIMAL* memory map
and a *VERY DELICATE* system. If your LED is not mapped via something
like a spare BAT, trying to toggle the LED after the RFI and before the
LED is (re)mapped in your virtual address space *will* crash your system.
Likely problems for crashing:
* Your MMU-controlled memory map is not set up correctly.
* Big unknown, lots of ways to screw this up
* You are inadvertently accessing something that isn't mapped yet
* Debug LED
* Board-specific hardware
* Other hardware
This is the #1 hardest part of getting linux to run, magnified 10x
because you don't have a hardware debugger (it is very tricky _with_ a
hardware debugger).
On the positive side, lots of people have done this successfully. If
you limit your initial changes to the absolute bare minimum and review
each one carefully, you can get past this even with just a LED for
debugging. If you cannot acquire a debugger (or while you are waiting
for FedEx to deliver it tomorrow ;-), review what is mapped and how it
is mapped between the RFI that turns on the MMU and when the MMU is
fully set up. During this delicate period, your code is likely
accessing something that is not mapped.
Good luck,
gvb
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2007-03-15 11:50 ` Jerry Van Baren
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