Hi!
9-Авг-2006 11:54 [EMAIL PROTECTED] (Japheth) wrote to
freedos-devel@lists.sourceforge.net:
>> If you mean "optional" in that there should an option added (post-1.0) to
>> control A20 for potentially complex machinations (e.g. directly accessing
J> I meant the first, but also think this option should be implemented pre-1.0.
J> The current implementation seems very simple, for example, the XMS functions
J> to enable disable A20 usually increase/decrease a counter which must go to
J> zero to indeed disable the gate.
This is to enable nested calls.
J> I didn't find such a counter in the current Emm386.
Hm. You right - enable/disable currently performed unconditionally,
contradicting to:
"
* Drivers should control the A20 line via an "enable count." Local
Enable only enables the A20 line if the count is zero. It then
increments the count. Local Disable only disables A20 if the count
is one. It then decrements the count. Global Enable/Disable keeps
a flag which indicates the state of A20. They use Local
Enable/Disable to actually change the state.
"
J> So it may be very easy to disable A20 with FD-Emm386 just by calling
J> the enable/disable XMS function pair.
Yes. :(
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