
2-22
Computer Group Literature Center Web Site
Raven PCI Host Bridge & Multi-Processor Interrupt Controller Chip
2
Figure 2-6. PCI Spread I/O Address Translation
Spread I/O addressing allows each PCI device’s I/O registers to reside on
a different MPC memory page, so device drivers can be protected from
each other using memory page protection.
All I/O accesses must be performed within natural word boundaries. Any
I/O access that is not contained within a natural word boundary will result
in unpredictable operation. For example, an I/O transfer of four bytes
starting at address $80000010 is considered a valid transfer. An I/O
transfer of four bytes starting at address $80000011 is considered an
invalid transfer since it crosses the natural word boundary at address
$80000013/$80000014.
Generating PCI Configuration Cycles
The Raven uses configuration mechanism #1 as defined in the PCI Local
Bus Specification 2.0 to generate configuration cycles. Please refer to this
specification for a complete description of this function.
Configuration mechanism #1 uses an address register/data register format.
Performing a configuration access is a two step process. The first step is to
place the address of the configuration cycle within the
CONFIG_ADDRESS register. Note that this action does not generate any
cycles on the PCI bus. The second step is to either read or write
1915 9702
MPC A Offset
31
12 11
5 4
0
31
0
PCI Address
25 24
0 0 0 0 0 0 0
0
0
0
0
0
0
0
5 4