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2-14
Computer Group Literature Center Web Site
Raven PCI Host Bridge & Multi-Processor Interrupt Controller
2
The resource at $CF8 is a 32 bit configuration address port and is referred
to as the CONFIG_ADDRESS register. The resource at $CFC is a 32 bit
configuration data port and is referred to as the CONFIG_DATA register.
Accessing a PCI functions’s configuration port is a two step process;
❏
Write the bus number, physical device number, function number
and register number to the CONFIG_ADDRESS register.
❏
Perform an I/O read from or a write to the CONFIG_DATA register.
Generating PCI Special Cycles
To prime Raven to generate a special cycle, the host processor must write
a 32-bit value to the CONFIG_ADDRESS register. The contents of the
write are defined later in this chapter under the CONFIG_ADDRESS
register definition. After the write to $CF8 has been accomplished, the
next write to the CONFIG_DATA register causes the Raven to generate a
special cycle on the PCI bus. The write data is driven onto AD[31:0]
during the special cycle’s data phase.
Generating PCI Interrupt Acknowledge Cycles
Performing a read from the PIACK register will initiate a single PCI
Interrupt Acknowledge cycle. Any single byte or combination of bytes
may be read from, and the actual byte enable pattern used during the read
will be passed on to the PCI bus. Upon completion of the PCI interrupt
acknowledge cycle, the Raven will present the resulting vector information
obtained from the PCI bus as read data.
Endian Conversion
The Raven supports both big- and little-endian data formats. Since PCI is
inherently little-endian, conversion is necessary if all PPC devices are
configured for big-endian operation. The Raven may be programmed to
perform the Endian conversion described below.