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
216
Section 8: PCI Bus and HyperTransport Fabric
Document
1250_1125-UM100CB-R
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shows the queueing for DMA accesses from the HyperTransport fabric and PCI bus into the part.
Figure 45: Buffers Used for DMA Accesses from the PCI and HyperTransport
Posted writes from the HyperTransport fabric flow through the queues in the I/O bridge and ZBbus interface
and are posted on the ZBbus. Non-posted writes from the HyperTransport become posted writes internally
(since the architecture does not have any internal non-posted writes). An acknowledgment response is always
sent on the HyperTransport when the write leaves the HyperTransport interface and is inserted in the I/O bridge
queue. Since it has become a posted write it may now pass reads. An error response will never be generated.
Reads from the HyperTransport fabric pass through the queues and are sent onto the ZBbus. The I/O bridge
interface can have 8 reads outstanding on the ZBbus (including those from both PCI and HyperTransport).
When all 8 entries in the RDR buffer are in use further reads are blocked from moving into the ZBbus request
queue. The read-data-return is sent back to the CPU response queue in the HyperTransport interface. Read
requests from the HyperTransport that are longer than 32 bytes will result in two reads being issued towards
the ZBbus.
Queue up to 4
Posted
Queue up to 4
Non-Posted
HT
Queue
Queue
Queue
Queue
PCI
Queue
Queue
Request
1 Outstanding RDR
Prefetch 1 Block for Read/Readline
Prefetch 2 Blocks Read Multiple
8 RDR
Outstanding
ZBbus
4 RDR
2 Write
2 Requests
2 Requests
2 Writes
1 RMW