2. Interface Operation
33
Tsi308 User Manual
80D4000_MA001_02
Tundra Semiconductor Corporation
www.tundra.com
2.2.1.1
Packet Decode
As packets arrive from a HT link, the associated commands and addresses are decoded to
determine if the Tsi308 is the packet target on HyperTransport chain and routed to the
appropriate port where they are locally stored. Packets are checked in the destination port for
ordering collisions against other packets resident in the buffers. The decode and collision results
are stored in the buffers with the packets. The packet routing is as follows:
•
Packets received on the HyperTransport interface may be routed to internal logic (CSRs),
including PCI-X interfaces. This is “accepting” a packet.
•
Packets may also be routed to the other HyperTransport link interface for transmission to
the next device in the chain. This is “forwarding” a packet.
•
A particular packet may be accepted, forwarded, or both.
The Tsi308 HyperTransport packet decode first determines whether the incoming packet is
traveling upstream or downstream. This determination is based on the packet source
information contained in the packet itself, not on which link is the upstream or downstream link.
•
Upstream packets are always forwarded toward the host and are never accepted by the
Tsi308 chip.
•
Downstream RdSized and WrSized request packet addresses are decoded according to the
HyperTransport Address Map described in Section 3.3 and are accepted if they match any
Tsi308 address ranges of any PCI-X ports or internal CSRs.
•
Downstream WrSized and RdSized that do not match any of the Tsi308 address ranges are
forwarded to the next device in the chain.
•
Broadcast request addresses are also decoded and accepted if they match a Tsi308 address
range. However, these packets are also always forwarded.
•
Fence and Flush requests are never accepted by Tsi308 and are always forwarded.
•
Downstream response packets are accepted if their UnitID field matches the value in the
BaseUnitID field of any of the Tsi308 LdtCmd register; otherwise, they are forwarded.
2.2.1.2
Collision Checking and Ordering
Collision checking is performed according to the HyperTransport protocol to determine if
incoming packets are required to stay ordered behind packets already in the Rx buffers. Only
packets headed to the same accept or forward destination may have ordering requirements. If a
packet has an ordering collision, it may not be issued from the Rx buffers until the packet with
which it collided has both been issued and reached an appropriate commit point to guarantee
ordering. This ordering point varies by destination.
Содержание TSI308
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