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 Tue, Sep 07, 2004 at 08:15:47PM -0400, Trellix78@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.
That's controlled by the descriptor table flags for the particular descriptor in use. (cs/ds/es)
Trying to write to protected memory would cause a page fault that LB probably doesn't recover from. (Are PF:s handled at all?)
//Peter
On Wed, 8 Sep 2004, Peter Stuge wrote:
On Tue, Sep 07, 2004 at 08:15:47PM -0400, Trellix78@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.
That's controlled by the descriptor table flags for the particular descriptor in use. (cs/ds/es)
ah,well, sorta.
There are north bridge issues. There are lots of ways in the x86 architecture for writes to fail ...
Trying to write to protected memory would cause a page fault that LB probably doesn't recover from. (Are PF:s handled at all?)
no, that's not necessarily the case ...
ron
At 01:15 08/09/2004, Trellix78@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)
Cheers
Ian
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Ian Smith -
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Ronald G. Minnich -
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