epia m vga + memcpy failed

Ian Smith ian at abelon.com
Wed Sep 8 02:26:01 CEST 2004

At 01:15 08/09/2004, Trellix78 at aol.com wrote:
>That message is from the original freebios.  I was thinking that shadowing 
>is not corretly set up and that maybe the
>segment is write-protected.  After setting up shadowing,
>the chipset my turn on write protection by default, anyway.  I don't know 
>how to turn write protection off specifically for the C00000 segment.  So 
>far, the only reference that I can find about write protection is in the 
>Pentium developer's manual. It says to have bit 16 of CR0 be zero to turn 
>off write protection.

On the VIA VT8622/8623 you need to write 0xFF to Device 0, offset 0x61, and 
this will write enable the shadow RAM area 0xC0000-0xCFFFF. To write 
protect it afterwards write 0xAA to the same register.

BTW - according to the datasheet both read and write are disabled by 
default (same goes for all shadow RAM areas)



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