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Hello.

I want to use the A20 address line using this [1] BIOS function.
But I whether know what a keyboard controller's "secure mode" is,
nor how to disable it...
I've been looking for an implementation of this function or some
documentation about it, but I couldn't find any.
So, can you please explain what this "secure mode" is and how to
disable it, or give me a good hint?

Thanks,
Jan


[1] (An extract from Ralph Brown's Interrupt List)
=> http://www-2.cs.cmu.edu/afs/cs/user/ral ... files.html

INT 0x15 - SYSTEM - later PS/2s - ENABLE A20 GATE
ax = 0x2401
Return: CF clear if successful
ah = 0x00
CF set on error
ah = 0x01: keyboard controller is in secure mode
ah = 0x86: function not supported