IDT 89HPES64H16G2 User Manual page 63

IDT Switch Core
Notes
PES64H16G2 User Manual
As the TLP flows through the switch, its alignment or contents may be modified. In all such cases, parity
is updated and not recomputed. Hence, any error that occurs is propagated and not masked by a parity
regeneration. When the TLP reaches the DL layer of the switch egress port, parity is checked and in parallel
an LCRC is computed. If the TLP is parity error free, then the LCRC and TLP contents are known to be
correct and the LCRC is used to protect the packet through the lower portion of the DL layer, PHY layer, and
link transmission.
If a parity error is detected by the DL layer of an egress port, then the TLP is nullified by inverting the
computed LCRC and ending the packet with an EDB symbol. Nullified TLPs received by the link-partner are
discarded. In addition to nullifying the TLP, the End-to-End Parity Error (E2EPE) bit is set in the Internal
Error Status (IERRORSTS) register. The DL layer never replays a TLP with a sequence number different
from that initially used. If a parity error is detected during a DL layer replay, then all TLPs in the replay buffer
are flushed.
In addition to TLPs that flow through the switch, cases exist in which TLPs are produced and consumed
by the switch (e.g., configuration requests and responses). Whenever a TLP is produced by the switch,
parity is computed as the TLP is generated. Thus, error protection is provided on produced TLPs as they
flow through the switch. In addition, parity is checked on all consumed TLPs. If an error is detected, the TLP
is discarded and an error is reported by setting the E2EPE bit in the IERRORSTS register.
A parity error reported at a switch port cannot be definitively used to identify the location within the
device at which the fault occurred as the fault may have occurred at another port, in the switch core, or may
have been generated locally (i.e., for ingress TLPs to the switch core which are consumed by the port such
as Type 0 configuration read requests on the upstream port).
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