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Re: 68000/RTEMS question..

On 20 Jul 1998, 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).

It easier than this.  All you need to do is map the ROM at both its
correct address and at address 0 from reset until the first processor
write.  If you don't want supervisor code in RAM, you could also
permanently map the ROM at address 0 in the Supervisor Program Space.

Peter Jeremy (VK2PJ)          
Alcatel Australia Limited
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