Incoming slave accesses are mapped and controlled by two incoming scatter-
gather maps:
•
For A32 accesses, a Digital Alpha VME 4 system occupies up to 128 MB of
memory mapped by 16384 scatter-gather entries, each mapping an 8 KB
page.
•
For A24 accesses, a Digital Alpha VME 4 system occupies up to 16 MB
mapped by 2048 scatter-gather entries, each mapping an 8 KB page.
Figure 10–6 Mapping Pages of Memory from VMEbus to PCI Bus
ML013376
4 GB
Mem Space
8 Kb
PCI
A32
VME
A24
A16
Scatter-Gather
Mapping
10.2.1 Decoding Addresses
The VME-to-PCI address decoding is implemented using CY7C964 bus interfaces
within the VME interface. Three CY7C964 bus interfaces are accessed together
in the VMEbus i/f address base (VIF_ABR) and VMEbus i/f address base mask
(VIF_MASK) registers. The registers must be accessed as longwords even though
the individual bytes represent address match data for separate VME address
spaces.
10–10 VME Interface
Summary of Contents for Digital Alpha VME 4/224
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