Robust SerialExpress properties
Robust properties of the interconnect include:
- Signal isolation. DC-isolation circuits
isolate the receiver from
- Power isolation. Green-wire grounds are never shorted together
through cable connections, reducing the possibilities of fused
shields and/or connectors within industrial environments.
- Error monitoring. Transmission errors are logged and
camouflaged when first detected, allowing marginal links to be
readily identified by checking software-visible error logs.
- Fault retry. Local identifier tags enable the use of hardware
fault retry, when used as duplicate-suppression labels. Although
this feature is optional, it is viewed as critical for the
high-bandwidth links that are expected to have higher error rates.
- Cable loops. Redundant connections
(cable loops) are
allowed. This simplifies installation procedures and allows the
system to remain operational when cables are lost in normal
- Soft nodeId identifiers. Nodes have two identifiers: a
set-by-hardware hardId and a set-by-software hardId. Bus resets
that change the cable topology may reassign new hardId values, but
the previously-assigned softId values are maintained. Thus,
software doesn't have to cancel outstanding context-senstive I/O
operations when new devices are added or removed.
- Isochronous. Isochronous transfers are failure tolerant in
- Clock synchronization. Alternate clock masters are
automatically activated during the absence of clockSync
packets/. Clock accuracy is maintained, because local crystals
can sustain their accuracies through the loss of a few
- Data transfers. Sending of small isochronous packets
simplifies the isochronous hardware fault-retry protocols, by
reducing the isochronous bandwidth that must be prereserved for
hardware fault-retry purposes.
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Last modified: May 4, 1997