12.6. NuBus
Another interesting, but nearly forgotten, interface bus is NuBus. It
is found on older Mac computers (those with the M68k family of CPUs).All of the
bus
is memory-mapped (like everything with the M68k), and the devices are
only geographically addressed. This is good and typical of Apple, as
the much older Apple II already had a similar bus layout. What is bad
is that it's almost impossible to find documentation
on NuBus, due to the close-everything policy Apple has always
followed with its Mac computers (and unlike the previous Apple II,
whose source code and schematics were available at little cost).The file drivers/nubus/nubus.c includes almost
everything we know about this bus, and it's
interesting reading; it shows how much hard reverse engineering
developers had to do. |
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