68000/RTEMS question..

[Joel Sherrill]

On 20 Jul 1998, James Youngman wrote:

> >>>>> "ts" == Tomaz Stih <tomaz.stih@triglif.com> 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).

I have seen this on a number of VMEbus boards.  I seem to recall that the
MVME135 and DMV152 do this.  It must be a common trick.  I suppose it is
natural to want RAM addresses in low memory.

--joel
Joel Sherrill                    Director of Research & Development
joel@OARcorp.com                 On-Line Applications Research
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