From: james.harris.1@gmail.com   
      
   On 21/07/2021 07:02, wolfgang kern wrote:   
   > On 20.07.2021 19:56, James Harris wrote:   
      
   ...   
      
   >>> all my machines don't even have an A20 gate anymore, since 2010.   
      
   ...   
      
   >>> but I kept the few bytes to check ffff:0010 isn't equal to 0:0.   
   >> Very sensible. It's virtually cost-free assurance.   
   >   
   > it was cheaper to keep it :)   
   > ; push -1   
   > ; pop es          I need this four anyway   
   > ; push 0          done during boot once   
   > ; pop ds   
   > 66 A1 00 00       mov eax,[0000]   
   > 36 66 3B 06 10 00 cmp eax,[es:0010]   
   > 74 xx             JZ ... ;A20 failed   
      
   Presumably you know those locations cannot be equal. I have code which   
   does something similar to yours   
      
      mov ax, [A20_TEST_WORD]   
      cmp ax, [es: A20_TEST_WORD + 16]   
      jne .enabled   
      
   but in case the values just happen to be the same I follow it with   
      
      not ax                   ;Set a different value   
      mov [A20_TEST_WORD], ax   
      cmp ax, [es: A20_TEST_WORD + 16]   
      not ax                   ;Get back old value (without changing flags)   
      mov [A20_TEST_WORD], ax  ;Restore memory (without changing flags)   
      jne .enabled             ;Branch on result of the compare instruction   
      
      
   which I expect you regard as bloat! :-)   
      
      
   --   
   James Harris   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)