Hi!
16-Авг-2006 13:19 [EMAIL PROTECTED] (Michael Devore) wrote to
freedos-devel@lists.sourceforge.net:
MD> 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.
May you explain here and/or, better, in comments in source, why
decreasing SP solves issues (and which issues there are)?
>>Only plausible explanation:
>>THIS BIOS damages (sometimes ?) the flags;
Do you mean "flags, _saved on the stack above given code_"? And, if so,
then why flags are damaged, but return value, which was lies on place of
flags (relative SP) are not damaged, if you comment out "pushf"?
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