2. Interface Operation
34
Tsi308 User Manual
80D4000_MA001_02
Tundra Semiconductor Corporation
www.tundra.com
Because the Outbound Request Controller (ORC) can reorder requests, requests accepted by the
Tsi308 may not be committed until they are retired by ORC. For accesses to PCI-X bus, this
means that the request reached the PCI-X bus and all data was transferred. Packets forwarded
from one link to the other are either streamed – meaning that the transmission may start before
the whole packet is received or a complete packet is first stored and then forwarded, avoiding
possible “holes” on transmitting link if transmitting link bandwidth (link frequency * link
width) is an order faster than that of receiving link. Since there is no specification defined way
to determine the bandwidth of receiving link, Tsi308 implements a proprietary control bit
(StoreForward) per link in its CSR which system software can program that tells the Tsi308
whether to stream (low latency) or not. It is the Rx Command Buffer’s responsibility to ensure
that required packet ordering is maintained so packets can be committed as soon as they are
passed to the link controller.
Packets that do not have any ordering requirements may leave the Rx buffers in a different order
than they reached them, both among and within virtual channels. In general, Rx buffers select a
packet choosing the oldest non-blocked packet in each channel to a given destination.
HyperTransport Ordering
lists ordering implemented in Tsi308 for packets issued from PCI/PCI-X to
HyperTransport link and for packets forwarded from one HT link to other HT link.
Table 2: HyperTransport Ordering
Row Pass Column
Posted Request
Non-posted Request
Response
Posted Request
No
Yes
Yes
Non-posted Request
No
No
No
Response
No
Yes
No
Summary of Contents for TSI308
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