How to enable RW on shadow RAM area on I945 chipset?

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gabiz_ro

Joined: 20 Feb 2010
Posts: 66

gabiz_ro 14 Sep 2010, 20:32

I want for some tests to enable read-write on some areas of RAM which is locked by BIOS.

Reading datasheet of Intel 945 chipset I see this can be done changing value of offset 92h of device 0 function 0
But my attempts was unsuccesfull until now.

Under windows I can write that using PCIScope so probably isn't read only that offset.

can somebody help me?
Thanks.

14 Sep 2010, 20:32

baldr

Joined: 19 Mar 2008
Posts: 1651

baldr 14 Sep 2010, 20:53

gabiz_ro,

Have you tried it clean (from boot sector / DOS)? Windows is quirky in its attempts to virtualize 00000-FFFFF. My current 865PE have C8000-CFFFF controlled by PAM2 too, probably I'll do some tests later.

14 Sep 2010, 20:53

gabiz_ro

Joined: 20 Feb 2010
Posts: 66

gabiz_ro 14 Sep 2010, 21:01

I have tried before OS load.
Maybe I do something wrong since I'm not a programmer.

Code:

    mov eax,080000092h       
    mov dx,0CF8h            
    out dx,eax         
    mov dx,0CFCh   
    in al,dx          
    mov al, 33h       
    out dx,al

14 Sep 2010, 21:01

baldr

Joined: 19 Mar 2008
Posts: 1651

baldr 14 Sep 2010, 21:35

gabiz_ro,

PCI configuration space is mapped dword-wise (i.e. bits 0 and 1 written to 0xCF8 are 00). Use something like the following:

Code:

mov     eax, 0x8000'0090
mov     dx, 0xCF8
out     dx, eax
mov     dx, 0xCFC+2
in      al, dx
or      al, 0x33
out     dx, al

14 Sep 2010, 21:35

gabiz_ro

Joined: 20 Feb 2010
Posts: 66

gabiz_ro 14 Sep 2010, 21:46

I this time I try other ways and write OK
I write 33333330h at 80000090h now enabled RW on many other regions and one of my problem was solved.
Thanks for your help.

14 Sep 2010, 21:46

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