In article <zkessin.726802574@chaos.cs.brandeis.edu>, zkessin@chaos.cs.brandeis.edu (Zach K) writes...
>> I have been trying to figure out how to boot on a 68000/008/010 and
>> have seen various methods of figuring out how to have rom at $0000 but
>> ram at $008-$3FF, one thing I noted was that the restart vectors are
>> in the supervisor program space while everying else is in supervisor
>> data, so can I use the fc[0-2] pins to remap the low few words of the
>> address space in supervisor program only to somewere else in my
>> address map.
>>
>> Does this idea make sense? it seams easer than trying to have the
>> computer on boot clear a bit somewere and in doing so remap the rom?
>>
>> any ideas?
>>
>> ps is there a FAQ for this group? in not mabey we should have one.
>>
>> --Zach
>> Zachary Kessin zkessin@cs.brandeis.edu
>> real.world: I don't think the news server gets that group!
One real simple hack is what the Sage's and Stride's do: ROM is at high memory and RAM is at low memory. On reset, the RAM is shadowed by the ROM. As soon as the ROM is addressed in its proper address space ($FFxxxxxx), the shadowing is disabled and RAM is available starting at $00000000... No need to count bus cycles, etc. You can just use the existing decode line for ROM to set a FlipFlop (that is cleared by the reset circuit and whose output diddles the shadowing logic). Of cource the first thing
the ROM does is initialize the vector table to something meaningfull (or at least the important vectors (bus error, address error, etc.)
