before i5 I was able to write to C0000 (video bios shadow) space by setting PAM registers to unlock and re-lock this address space. In documentation for new chipsets it says the following:
The 13 sections from 768 KB to 1 MB comprise what is also known as the PAM Memory Area. Each section has Read enable and Write enable attributes. The CPU documentation will now contain the registers and decode rules/restrictions.
The PAM registers have moved to the CPU. For the PAM register details, refer to CPU documentation.
After a long search in system programming guides I am still unable to find a way to write to this memory range.