User Manual
BCM1250/BCM1125/BCM1125H
10/21/02
B r o a d c o m C o r p o r a t i o n
Document
1250_1125-UM100CB-R
Section 8: PCI Bus and HyperTransport Fabric Page
221
H
YPER
T
RANSPORT
F
ABRIC
TO
PCI B
US
Requests received by the HyperTransport interface to any addresses that fall in the space allocated to the PCI
memory space (regions A and C in
) or that fall into the special double ended chain
mapped address ranges (
E0_4000_0000
-
E0_7FFF_FFFF
and
F0_0000_0000
-
F0_FFFF_FFFF
in
) will be forwarded to the PCI interface. Since the size of the transfer is specified at the
start of a HyperTransport request the access to the PCI bus will always be for the exact number of bytes
requested.
shows the queues used in peer-to-peer operations with a HyperTransport master.
Peer-to-peer writes will always be posted to the PCI bus. Non-posted write requests will be acknowledged
when they leave the HyperTransport interface. Writes flow in their own channel from the HyperTransport
interface to the PCI interface and may pass non-posted reads.
Figure 48: Buffers Used for HyperTransport to PCI Peer-to-Peer Accesses
The HyperTransport interface can have two reads outstanding to the PCI interface. If a HyperTransport request
is for more than 32 bytes both outstanding reads are needed to service it. Alternatively two smaller requests
can proceed together. The buffering and PCI interface will maintain the ordering of the reads. The request path
and RDR buffer in the PCI interface are shared with PIO and DMA requests, but there are dedicated return
buffers for the peer-to-peer RDR.
Queue
Queue
1 Write
Queue
1 Read
Queue
If Reads Queue 1 WR
Queue
2 RDR
Queue
Queue
Else
5 WR Queue
Issue to
Queue
PCI Bus
Up to 4 Posted
Up to 4 Non-Posted
2 RD
1 RDR
HT
PCI
Issue
1 Peer-Peer Read for 32 Byte Req
2 Peer-Peer Read for 64 Byte Req
1 RDR
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