Table Branching in assembly

Comments

• tekochip Posts: 56

  2007-04-27 20:51 edited 2007-04-27 20:51

  Got it, I needed one more level of indirection:
  
  add jumpPtr, par 'Grab the offset
  movs :dest, jumpPtr 'Pointing at
  nop
  :dest
  movs :dest1, jumpPtr 'now what I'm pointing at
  nop
  :dest1 jmp jumpPtr
• Kaio Posts: 274

  2007-04-27 21:10 edited 2007-04-27 21:10

  Chip,
  
  you could have a look at file AsmDebug.spin of POD, where I pass the command to jump to the related subroutine. I have used a jump table for this while it is the easiest way and you can save memory which is otherwise used to get the address from table.
• Kaio Posts: 274

  2007-04-27 22:12 edited 2007-04-27 22:12

  I have separated the code which I was using in POD.
  

                          rdbyte  Command,par             'get command value in range 0 - 3
                          add     Command,#cmdJumpTable
                          movs    :jmpCmd,Command
                          nop
  :jmpCmd                 jmp     #0-0                    
  cmdJumpTable            jmp     #subroutine0
                          jmp     #subroutine1
                          jmp     #subroutine2
                          jmp     #subroutine3
  '-----------------------
  subroutine0             nop
  '-----------------------
  subroutine1             nop
  '-----------------------
  subroutine2             nop
  '-----------------------
  subroutine3             nop
  
  Command                 res     1
  
  
  
• tekochip Posts: 56

  2007-04-28 02:15 edited 2007-04-28 02:15

  Much cleaner, thanks.
• Gary Preston Posts: 6

  2007-04-28 11:30 edited 2007-04-28 11:30

  Have a look at the parallax graphics driver code, it has a jumptable setup using bytes to minimise the space used. It reads a command from PAR then jumps to the address held in the jmp table.