4Links Multi-link SpaceWire Recorder Version 4 User Manual page 11


The MSR electrically connects each pair of ports together, just imposing a buffering delay of about 7 ns to
the signals propagating between each of these ports. No re-clocking of the signals is performed in this
buffer. Remember that SpaceWire cables introduce a delay of about 5 ns per metre, so the extra cabling
in a monitored link might present a similar delay to that of the MSR itself. The MSR is thus a passive
repeater of the traffic on the SpaceWire links - it does not modify the signals other than by electrical
buffering. Thus, no SpaceWire tokens are injected onto a link by the MSR.

The MSR internally maintains state machines to keep track of the SpaceWire links, but these are purely
used for reporting purposes. It cannot control the start-up of a link, so if it is enabled after a link is
established, it is unable to synchronize to that data stream. The MSR therefore needs to be booted before
the link is connected, but not necessarily running the msr software yet. If, for any link, the MSR's front-
panel display shows the link speed in each direction, as well as the exchange of NULL tokens, flow-control
tokens or data characters (as in figure 2.3), then it will be able to record from that link.

Traffic on SpaceWire links, with speeds up to 400 Mb/s, may be recorded.

Traffic on the SpaceWire links being monitored may be captured and written to a file using the msr
program provided (see section 9.2, "Data Capture using the msr Program"). The basic MSR device
records the SpaceWire packet bytes and EOP / EEP framing markers that were observed on each direction
of the attached links. Additional information is provided by the options described in section 2.4,
"Summary of MSR Options", below.

The front-panel display shows the state of the monitored links, even when the msr program is not
running.
Post-capture software (see section 9.3, "Data Inspection and Analysis using the read Program") can be used to
present the recorded traffic in an easily-readable textual form.
Figure 2.2: Connecting the MSR into a link under test
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