Decoding Addresses; Mapping Pages Of Memory From Vmebus To Pci Bus - DEC Digital Alpha VME 4/224 User Manual

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
PCI
4 GB
Mem Space
Scatter-Gather
Mapping
8 Kb

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
VME
A32
A24
A16
ML013376