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1.3 21164 Address Space
Figure 1–3 shows an overview of the 21164 address space. Figure 1–4 shows how
the 21164 address map translates to the PCI address space and how PCI devices
access the 21164 memory space using DMA transactions. The PCI memory space is
double mapped via dense and sparse space.
The 21164 I/O address map has the following characteristics:
•
Provides 4GB of dense
ory space.
•
Provides abundant PCI sparse
regions have byte granularity and is the safest memory space to use (that is, no
prefetching). Furthermore, the larger the space the less likely software will need
to dynamically relocate the sparse-space segments. The main problem with
sparse space is that it wastes 21164 address space (for example, 16GB of 21164
address space maps to 512MB of PCI sparse space).
The system provides three PCI sparse-space memory regions, allowing 704MB
of total sparse-space memory. The three regions are relocatable using the
HAE_MEM CSR. The simplest configuration allows for 704MB of contiguous
memory space.
–
512MB region, which may be located in any naturally aligned 512MB seg-
ment of the PCI memory space. Software programmers may find this region
sufficient for their needs and can ignore the remaining two regions.
–
128MB regions, which may be located on any naturally aligned 128MB seg-
ment of the PCI memory space.
–
64MB region, which may be located on any naturally aligned 64MB seg-
ment of the PCI memory space.
•
Limits the PCI I/O space to sparse space. Although the PCI I/O space can handle
4GB, most PCI devices will not exceed 64KB for the foreseeable future. The
system provides 64MB of sparse I/O space because address decoding is faster.
•
Provides two PCI I/O sparse-space regions: region A, which is 32MB and is
fixed in PCI segment 0–32MB; and region B, which is also 32MB, but is relocat-
able using the HAE_IO register.
1 Dense and sparse space address space are described later in this chapter.
1
address space to completely map the 32-bit PCI mem-
1
memory address space because sparse-space
21164 Address Space
System Address Space
A–7
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