DaniWeb IT Discussion Community - How to Switch into Protected Mode

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pdp8	Nov 25th, 2008 2:09 pm

How to Switch into Protected Mode

I need to make modifications to BIOS code which runs at PowerUp or Boot time and I need to access more than the lower 1,048,576 bytes of memory.

Is it possible to switch into Protected Mode at this time in order to access more memory? If so, how? What is the instruction sequence?

Alternatively, can anyone suggest a different approach?

Thanks,
Bob.

Salem

Nov 25th, 2008 5:49 pm

Re: How to Switch into Protected Mode

Perhaps you should begin by describing why you need the extra memory. Perhaps we could tell you about an alternative which uses less memory.

pdp8	Nov 26th, 2008 6:35 pm

Re: How to Switch into Protected Mode

Quote:

Originally Posted by Salem (Post 744646)

Perhaps you should begin by describing why you need the extra memory. Perhaps we could tell you about an alternative which uses less memory.

It's not that I need extra memory. What I want to do is read several bytes of data from the upper end of the 4GB address space, where an MD5 message digest of the bios will have been stored.

The intent is to compare the current MD5 with the pre-stored value to ensure that the BIOS has not been tampered with.

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