ARM926EJ-S MMU Problem in WinCE5.0

Hi all,

I'm developing a bootloader for ARM926 EJ-S, but there's a serious problem
need your help.
I've enabled MMU in bootloader in order to use virtual addresses.
But when I turn off MMU before jumping to the physical start address of
kernel, PC (porgram Counter) doesn't jump to the physical address I want.
It seems all instructions after turning off MMU cannot be fetched to execute
because PC is not there.

By the way,
I'm sure that MMU has been disabled because I've dumped the memory content
with physical address in ICE.

I don't know how to solve this problem, but I need this bootloader to bring
my WinCE OS image.

Hope there's someone could help me....
Thank you very much

Best Regards,
Sanjay

Silver
Sun Mar 16 17:17:47 PDT 2008

- clean the caches
- ensure that the CPU pipeline is full and that you jump to the physical
address at exactly the correct time. I am no sure how deep the prefetch
piece fo rthe pipeline is - I think 3 instructions but I put an extra NOP to
be safe.

See this (ARM926 TRM, section 2.3.8):
http://infocenter.arm.com/help/topic/com.arm.doc.ddi0198d/DDI0198_926_TRM.pdf


Try this:

; Physical target address, grab it now in case multiple instructions
are used
ldr r0, =PhyStart

; Test-Clean-Invalidate D-Cache
10 mrc p15, 0, r15, c7, c14, 3
bne %b10

; drain write buffer
mcr p15, 0, r1, c7, c10, 4

; Invalidate I-Cache (if you are using it)
mov r1, #0
mcr p15, 0, r1, c7, c5, 0

; MMU off procedure
mrc p15, 0, r1, c1, c0, 0
; disable M bit
bic r1, r1, #(1 :SHL: 0)
mcr p15, 0, r1, c1, c0, 0 <-- This turns the MMU off, the
pipeline will be prefetched already
nop
mov pc, r0
nop
nop

PhysStart
; get physical


Geoff
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