A–4
System Address Space
Address Map
The 21164 address space is divided into two regions using physical address <39>:
•
0 – 21164 access is to the cached memory space.
•
1 – 21164 access is to noncached space. This noncached space is used to access
memory-mapped I/O devices. Mailboxes are not supported.
The noncached space contains the CSRs, noncached memory space (for diagnostics),
and the PCI address space. The PCI defines three physical address spaces: a 64-bit
PCI memory space, a 4GB PCI I/O space, and a 256 byte-per-device PCI configura-
tion space. In addition to these three address spaces on the PCI, the 21164’s non-
cached space is also used to generate PCI interrupt acknowledge and special cycles.
The 21164 has visibility to the complete address space. It can access the cached
memory region, the CSR region, the PCI memory region, the PCI I/O region, and
the configuration regions (see Figure 1–1).
The PCI devices have a restricted view of the address space. They can access any
PCI device through the PCI memory space or the PCI I/O space; but they have no
access to the PCI configuration space. The system restricts access to the system
memory (for DMA operations) to the use of five programmable windows in the PCI
memory space (see Figure 1–1).
