BCM1250/BCM1125/BCM1125H
User Manual
10/21/02
B r o a d c o m C o r p o r a t i o n
Page
220
Section 8: PCI Bus and HyperTransport Fabric
Document
1250_1125-UM100CB-R
shows the queues used in peer-to-peer operations with a PCI master.
Peer-to-peer writes will transfer exactly the number of bytes written and will always be posted to the
HyperTransport fabric. They flow in their own channel from the PCI interface to the HyperTransport interface
and may pass non-posted reads.
Figure 47: Buffers Used for PCI to HyperTransport Peer-to-Peer Accesses
Peer-to-peer reads always assume the destination address is prefetchable (this is required for performance,
since the PCI bus does not give a good indication of the transfer size at the start of the transaction). Caution
should be used when accessing registers using peer-to-peer operations. The same algorithm is used as for
reads to the ZBbus, the PCI read is assumed prefetchable, and is a Read or ReadLine is causes single 32 byte
request to the HyperTransport fabric while a ReadMultiple will launch two requests.
Queue
1 Outstanding
RDR
PCI
Queue
Queue
Queue
Queue
14 Reads
Outstanding on HT Fabric
Queue
2 Write Requests
1 Write
1 Read
1 RDR
4 Posted
4 Non-Posted