Hi,
Arkady V.Belousov escribiÃ:
I can be missing something, but the enabling/disabling of an Address line of the processor affects physical adresses, and not logical or linear adresses. UMBs are remapped to another linear/physical adress that may lay beyond the 1MB physical address, and can thus be affected by the A20 enabling/disabling.MD> I don't think it affects anything important.
MD> As far as UMB's, I'm not sure if turning off the A20 line affects memory MD> mapping from physical odd-address Mb. Seems like it should,
Michael, strange to see such sentences from you. A20 is a pin of (186
and higher) CPU, which used to pass 21th bit of address. When this pin is
disabled, all access with addresses like FFFF:200 (which make 21-bit
address) are "wrapped" (by ignoring high 21th bit on A20 pin) to first 64k.
This shouldn't affect any addressing in the UMB, which lies below 1Mb.
I repeat that what I meant is to remap/not to remap the HMA adresses into the first 64Kb. Not more, not less.
Aitor
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