From: usotsuki@buric.co   
      
   On Tue, 28 Dec 2021, qkumba wrote:   
      
   > You'd be running already from 0000:7C00 if you're on a PC.  Your read   
   > will overwrite your existing code.   
      
   Yeah, knew that.   
      
   > Since all of the registers will have been set already for the first   
   > load, you could just   
   > mov ax, 0x201   
   > inc cx   
   > pushf   
   > push es   
   > push bx   
   > jmp far es:[0x004c]   
   > and forget about retry.   
      
   Hm. I was trying to think about how to emulate an INT by jumping (much   
   like the very common on the Apple ][ method of "return to subroutine",   
   which the ProDOS bootloader actually does use).  I guess that's what I was   
   looking for.   
      
   0100- B8 01 02        MOV   AX, 0201   
   0103- 41              INC   CX   
   0104- 9C              PUSHF   
   0105- 06              PUSH  ES   
   0106- 53              PUSH  BX   
   0107- EA 4C 00 00 00  JMP   0000:004C   
      
   12 bytes, eh?  That's far more efficient than I'd come up with. xD   
      
   > Otherwise, yes it's possible to have a polyglot bootsector, even on a   
   > 5.25".   
      
   Of course most Apple ][ media wouldn't work on a PC and vice-versa - the   
   1.44 MB floppy being the exception.   
      
   > As for the ProDOS loader, block 1 is "reserved" (=unused).  You could   
   > put the original sector there.  Then you wouldn't need to fit the actual   
   > loader in the boot sector.   
      
   Yeah, that's what I was hoping to be able to do: literally the Apple ///   
   trick, with a PC replacing the ///.   
      
   -uso.   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)