From: nowhere@never.at   
      
   On 12.07.2021 04:05, muta...@gmail.com wrote:   
      
   >> shifts. Or surely I can at least match the 80286 and do   
   >> (effective) 8-bit shifts. That would be a load of fun.   
   >> I guess it depends how many selectors I can define on   
   >> the 80386. I'll run everything in supervisor mode, so I   
   >> can use both GDT and LDT if that helps.   
      
   so why don't you stick to 386 and forget no more existing   
   old crap ?   
   > And if I can get the 8086 to trap and ignore db'66' and   
   > db'67' I will be able to have 16-bit executables that work   
   > on either shift value.   
      
   Now that's a really bad idea. compiled code may look like:   
      
   66 b8 44 33 22 11        MOV eax,imm32   
   67 03 84 11 55 44 33 22  ADD ax,[ecx+edx+d32]   
      
   so guess what's left w/o these prefixes:   
      
   b8 44 33                 MOV ax,imm16   
   22 11                    AND dl,[bx+di]   
      
   03 84 11 55              ADD ax,[si+d16]   
   44                       INC sp   
   33 22                    XOR sp,[[bp+si]   
      
   But IIRC 66 and 67 were ignored anyway on real 86/88.   
      
   > And since I want the OS to return to real mode to do   
   > BIOS calls, the 80386 is probably much better than the   
   > 80286 for this.   
      
   yes.   
      
   > But I believe the 80286 can do it anyway, with sufficient   
   > hardware support, and that would be a fun thing to do   
   > as well.   
      
   no. I wont recommend to use a solder iron on CMOS CPUs.   
   __   
   wolfgang   
      
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