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Re: 68000/RTEMS question..

In a message dated 20-Jul-98 15:56:16
   James Youngman <> wrote:

>>>>>> "ts" == Tomaz Stih <> writes:

  ts>> When dealing with 68000 boards with no vector base register
  ts>> there is a problem with setting vectors because it is common
  ts>> to put ROM at 0x0000 address where vectors reside thus making
  ts>> it impossible to change them.

>00000000 does not have to be ROM.  You just have to be able to load 8
>bytes from it at reset time.   I've seen boards by Pro-Active Control
>which use a counter to change the memory mapping after the right
>number of bus cycles to that the vectors can be in RAM (except,
>effectively, the reset vector).

 An "interesting" note might be that (M68K) Amiga-computers has RAM at address
0, still they do bootstrap from ROM ;-}
 I don't know *how* the hardware (RAM/ROM switch) is implemented, though.

   ,-.         /   \
  /   \       /     \
 /Hannu E K Nevalainen     ,-.
' \   /   `-*              _ // 1985+
         `-'           `-'                     \X/Amiga user
Personal rc5-stats: 6,717 2^28-key blks, i.e. 1,803,080+ Mkeys, M68K Amiga.
The complete Amiga memory map:  AbsExecBase == 4L