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ARM920T MMU configuration

Alexander Varnin
Note: This was originally posted on 16th August 2010 at http://forums.arm.com

Hello. I'm making boot loader for arm board SMDK2443 based on ARM920T. There is 128 Mb of RAM on board, and i set up MMU to map addresses 0x80000000-0x88000000 as sections to physical 0x30000000-0x38000000. But for some reason addresses in upper part of address space point to the same physical address that in the lower part.
I.e. running following code
char *p1 = 0x835a0000,
   *p2 = 0x875a0000;

*p1 = 1;
printf("p1 == %x\t*p1==%x\n", p1,*p1);
*p2 = 2;
printf("p2 == %x\t*p2==%x\n", p2,*p2);
printf("p1 == %x\t*p1==%x\n", p1,*p1);
makes output:
p1 == 835a0000 *p1==1
p2 == 875a0000 *p2==2
p1 == 835a0000 *p1==2


Of course, this makes mess for operating system, and it doesn't boot.

Can you tell me, what could be the reason of such behavior?
Parents
  • Note: This was originally posted on 17th August 2010 at http://forums.arm.com

    What are your page table entries for 0x835X,XXXX and 0x875X,XXXX?

    Here is my mmu table attached. As you can see

    ...
    835:  33500c1e
    ...
    875:  37500c1e
    ...


    As i try turning off mmu, i'll tell you result.
    Upd: I don't know if i can manage to write something, turning off MMU, because printf function is not available in that case.
Reply
  • Note: This was originally posted on 17th August 2010 at http://forums.arm.com

    What are your page table entries for 0x835X,XXXX and 0x875X,XXXX?

    Here is my mmu table attached. As you can see

    ...
    835:  33500c1e
    ...
    875:  37500c1e
    ...


    As i try turning off mmu, i'll tell you result.
    Upd: I don't know if i can manage to write something, turning off MMU, because printf function is not available in that case.
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