From: Gideon Zweijtzer (gideonz_at_dds.nl)
Date: 2002-05-02 08:07:59
|Hello Gideon,
|
|>"thinking" that they are running from $0000-$ffff. Another feature will be
|>protection and bus-selection. The latter is necessary to define regions
|that
|>are not memory, but I/O. Memory accesses will go to the SDRAM bus, I/O
|>accesses to the original address/data bus.
|
|Memory accesses (at least selected ones) need also go to the original
|address/data bus elsewise the VIC chip will not see anything to display?
It is a good thing that you mentioned this. This means that the MMU
requires to have a mode to support writeback or write through to the I/O bus
as well. Of course it should be selectable, so that's up to the user to
program it in the MMU for which pages this applies (Note that on the C-64,
the bus bandwidth to memory is only 1 MB/s!! Fortunately, this is a lot
higher already on the C=1, but still less than the SDRAM bus). I would have
found out sooner or later, but it's better to include it in the design from
the beginning.
Gideon
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