

 ATAPI use of IDE registers
----------------------------

Offset     Read                       Write

00         Data register              Data register
04         Error register             Features register
08         Interrupt Reason register  Interrupt Reason register
0c         RESERVED                   RESERVED
10         Byte Count low             Byte Count low
14         Byte Count high            Byte Count high
18         Drive select               Drive select
1c         Status                     Command
20         Drive address              UNUSED
