At 03:21 PM 8/16/2006 +0200, tom ehlert wrote: >'solved' the original bug (sort of) by changing > >disable_enable_a20_BIOS: > ;pushf > ;cli > > shr ah,1 ; ah to 0 or 1 > mov al,24h > xchg ah,al ; ax == 2400h to turn off, 2401h to turn on > int 15h > > ;popf > pop ax > ret > >innocent change (it should behave EXACTLY the same), but now it works >after a while of headscratching, > >disable_enable_a20_BIOS: > pushf > sub sp,10 > cli > > shr ah,1 ; ah to 0 or 1 > mov al,24h > xchg ah,al ; ax == 2400h to turn off, 2401h to turn on > int 15h > > add sp,10 > popf > pop ax > ret > > >works, too. > >Only plausible explanation: >THIS BIOS damages (sometimes ?) the flags; and disabling >interrupts can have had serious consequences > >so preferring method fast over BIOS gives bios programmers less >chances to produce bugs
I love buggy BIOS situations. They make life so interesting. >just one thing: > >I noticed that (on this particular maschine), >enable_a20/disbale_a20 using method BIOS is extremely slow So, is the best answer to make your source changes for general distribution and keep BIOS moved close to the back of the line? It's hard to decide the best path for widescale distribution and we need to decide ASAP. I like your second version patch because it doesn't affect interrupt flags, although it's pretty weird that giving the interrupt a stack frame fixes the issue. Perhaps there's an unseen side-effect from somewhere else? Though I don't exactly see how that could work, unless it's chewing into problematic stack values. If BIOS control is demonstrated as buggy and slow as well, I definitely think that keeping it out of the first choice is the way to go. And making the (normally benign) stack frame code addition too. Gets my vote. Any other ideas or thoughts, anyone? ------------------------------------------------------------------------- Using Tomcat but need to do more? Need to support web services, security? Get stuff done quickly with pre-integrated technology to make your job easier Download IBM WebSphere Application Server v.1.0.1 based on Apache Geronimo http://sel.as-us.falkag.net/sel?cmd=lnk&kid=120709&bid=263057&dat=121642 _______________________________________________ Freedos-devel mailing list Freedos-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/freedos-devel
