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Computer Group Literature Center Web Site
Raven PCI Host Bridge & Multi-Processor Interrupt Controller
2
added to the 16 most significant bits of the PCI address, and the result is
used as the PPC address. This offset allows devices to reside at any PPC
address, independent of the PCI address map.
All Raven address decoders are prioritized so that programming multiple
decoders to respond to the same address will not be a problem. When the
PCI address falls into the range of more than one decoder, only the highest
priority one will respond. The decoders are prioritized as shown below.
PCI Configuration Space
The Raven does not have an IDSEL pin. An internal connection is made
within the Raven that logically associates the assertion of IDSEL with the
assertion of either AD30 or AD31. The exact association depends on the
state of the EXT02 pin when the RST* pin is released. If EXT02 is
sampled low, the Raven will associate AD30 with IDSEL. If EXT02 is
sampled high, the Raven will associate AD31 with IDSEL.
PCI Write Posting
If write posting is enabled, the Raven stores the target address, attributes,
and up to 128 bytes of data from one PCI write transaction and
immediately acknowledges the transaction on the PCI bus. This allows the
slower PCI to continue to transfer data at its maximum bandwidth, and the
faster PPC bus to accept data in high performance cache-line burst
transfers.
Only one PCI transaction may be write posted at any given time. If the
Raven is busy processing a previous write posted transaction when a new
PCI transaction begins, the next PCI transaction will be delayed (TRDY*
will not be asserted) until the previous transaction has completed. If during
a transaction the write post buffer gets full, subsequent PCI data transfers
Decoder
Priority
PCI Slave 0
highest
PCI Slave 1
PCI Slave 2
PCI Slave 3
lowest