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47 lines
1.9 KiB
Plaintext
47 lines
1.9 KiB
Plaintext
=== PTP transparent clock (P2P)
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ifdef::topdoc[:imagesdir: {topdoc}../../test/case/ptp/transparent_clock]
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==== Description
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Verify that an E2E or P2P Transparent Clock (TC) passes timing
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transparently through a hardware switch without adding a boundary-clock
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hop, and that the downstream time receiver converges to the
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grandmaster's time.
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Three nodes are connected in a chain: a grandmaster Ordinary Clock
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(priority1=1), a Transparent Clock with hardware timestamping, and a
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time-receiver Ordinary Clock (priority1=128).
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The TC updates the correction field in each Sync and Delay_Req message
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to account for its own residence time. Because a TC is transparent,
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the time receiver's steps-removed counter must equal 1 — unlike a
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Boundary Clock, which would give 2. A TC passes ANNOUNCE messages
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unchanged (stepsRemoved=0 from the GM), and the time receiver adds 1
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when it stores the value in currentDS, giving a total of 1. A BC
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increments stepsRemoved to 1 before forwarding, and the receiver adds
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1 more, giving 2. The time receiver's offset must converge within the
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tight threshold appropriate for hardware timestamping.
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The delay mechanism (E2E or P2P) is injected via the --delay-mechanism
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argument from the test suite YAML, allowing both variants to run from
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the same test script. The TC node requires hardware PTP timestamping
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support (capability: ptp-hwts).
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==== Topology
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image::topology.svg[PTP transparent clock (P2P) topology, align=center, scaledwidth=75%]
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==== Sequence
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. Set up topology and attach to DUTs
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. Configure grandmaster (OC, priority1=1, {dm})
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. Configure transparent clock ({dm.upper()}-TC)
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. Configure time receiver (OC, priority1=128, client-only)
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. Wait for grandmaster port to become time-transmitter
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. Wait for time receiver to reach time-receiver state
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. Verify time receiver steps-removed equals 1 (TC adds no boundary-clock hop)
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. Wait for time receiver offset to converge
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