TOS 2.06 modification for autoboot with twisted IDE cable

  IDE port addresses are changed when use twisted IDE cable. We need to use even instead odd port addresses. For instance Command/Status register will be $FFF0001C instead $FFF0001D.
 To having autobot with so attached drives some changes in TOS 2.06 code are required. Here are the new values (all just port addresses, low byte). A4 points to begin of TOS 2.06 (binary).


  move.b #$1C,$18A1(a4)
  move.b #$04,$18B7(a4)
  move.b #$08,$18C9(a4)
  move.b #$38,$18D7(a4)

  move.b #$1C,$18DF(a4)
  move.b #$08,$1905(a4)
  move.b #$38,$1913(a4)
  move.b #$1C,$191B(a4)
 
  move.b #$38,$1923(a4)
  move.b #$10,$1955(a4)
  move.b #$14,$195D(a4)
  move.b #$18,$1973(a4)

  move.b #$0C,$197D(a4)
  move.b #$18,$198F(a4)
  move.b #$38,$199B(a4)
  move.b #$1C,$19A3(a4)

  move.b #$18,$19FF(a4)
  move.b #$38,$1A13(a4)

  Total 18 locations.

ROM CRC check override:

  move.b #$60,$7F6(a4)
  Then it will be skipped, and no ROM CRC error message will appear after cold boot.

 RAM check skipping:    move.b #$60,$986(a4)

Better solution is to recalculate CRC checksum and write it in ROM image file. It can be done very easy with program ROMSPLIT. Get it here:
Open source Atari ST SW

PP