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*  If you find it necessary to program the hardware directly, then it is
   your responsibility to write code that will work correctly on the
   various models and configurations of the Amiga.  Be sure to properly
   request and gain control of the hardware resources you are
   manipulating, and be especially careful in the following areas:

*  Kickstart 2.0 uses the 8520 Complex Interface Adaptor (CIA) chips
   differently than 1.3 did.  To ensure compatibility, you must always
   ask for CIA access using the cia.resource/AddICRVector() and
   RemICRVector() functions.  Do not make assumptions about what the
   system might be using the CIA chips for.  If you write directly to
   the CIA chip registers, do not expect system services such as the
   trackdisk.device to function.  If you are leaving the system up, do
   not read or write to the CIA Interrupt Control Registers directly;
   use the cia.resource/AbleICR(), and SetICR() functions.  Even if you
   are taking over the machine, do not assume the initial contents of
   any of the CIA registers or the state of any enabled interrupts.

*  All custom chip registers are Read-only or Write-only.  Do not read
   Write-only registers, and do not write to Read-only registers.

*  Never write data to, or interpret data from the unused bits or
   addresses in the custom chip space.  To be software-compatible with
   future chip revisions, all undefined bits must be set to zeros on
   writes, and must be masked out on reads before interpreting the
   contents of the register.

*  Never write past the current end of custom chip space.  Custom chips
   may be extended or enhanced to provide additional registers, or to
   use bits that are currently undefined in existing registers.

*  Never read, write, or use any currently undefined address ranges or
   registers.  The current and future usage of such areas is reserved by
   Amiga, Inc. and is subject to change.

*  Never assume that a hardware register will be initialized to any
   particular value.  Different versions of the OS may leave registers set
   to different values.  Check the Amiga Hardware Reference Manual to
   ensure that you are setting up all the registers that affect your code.

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