At 02:46 PM 4/8/2004 -0400, Patrick J. LoPresti wrote: >Michael Devore <[EMAIL PROTECTED]> writes: > >> I added enable/disable test, but the report was that it still fails, >> after working for the startup test. Which either means the BIOS is >> bugged and fails under stress, or there is something very weird >> going on. > >Like the test_a20 code failing...
Yes, reversion to original A20 test is going to be the final mod tried before I declare the BIOS rogue, or possibly a subtle-bugged application. Although the new A20 test code should work, as it does fine in many machines and the logic is sound. I don't like the old A20 test since A20 status could be fooled by a driver or application caching the interrupt vector table image at zero-offset HMA. I'm not sure how likely that is, given other programs use the 256 byte compare method, but it seems theoretically possible. But hey, if it is more reliable, it's coming back. >The A20 gate defaults to disabled. So, assuming HIMEM64 is the first >program which tries to manipulate the gate, you can make "always on" >the FIRST test just by checking the state of A20. This is what the >Linux setup code does. I'm not sure FreeDOS can assume HIMEM has the first shot at machine hardware in its initial state. It certainly doesn't under VMware, which we have do FreeDOS users running under. Does VMware reset A20 back to known disabled state at startup of emulation session? What else might be in control of the machine before HIMEM, low level debuggers or virtual systems? Bochs? Others? Can we assume that they all play nice and set A20 to a known disabled stated during DOS startup? I don't know, maybe we can. ------------------------------------------------------- This SF.Net email is sponsored by: IBM Linux Tutorials Free Linux tutorial presented by Daniel Robbins, President and CEO of GenToo technologies. Learn everything from fundamentals to system administration.http://ads.osdn.com/?ad_id=1470&alloc_id=3638&op=click _______________________________________________ Freedos-devel mailing list [EMAIL PROTECTED] https://lists.sourceforge.net/lists/listinfo/freedos-devel
