Minutes for 0324: Use of Tick in List Execute state machine (802.1Q)

Standard: IEEE Std 802.1Q-2018 Clause: 8.6.9.4.16 Draft with fix: Submitted: 2021-05-06
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Date Meeting Text Status
2021-06-01 Jun 2021 Concall The request as briefly reviewed and it was agreed to requestor to attend the next maintenance call to further explain the request. Technical experts review
2021-06-08 8 Jun 2021 Concall The requestor reviewed the parts of 802.1Q that highlight the issue. The main concern is with the Note that follows the text describing the implementation of the Tick boolean variable. The non-normative note references the TickGranularity managed object which is intended to provide the actual granularity of the Tick clock in units of 1/10 of ns. However, the Tick variable is intended to run on 1ns intervals and the state machine current depends on this specification, so having a TickGranularity other than 1ns creates a problem for the operation of the state machine. Simply deleting the Note is not a sufficient resolution to the issue. There was some discussion about when this text was introduced in Qbv and a reference to comment #15 of Qbv/d2.1 was provided: https://www.ieee802.org/1/files/private/bv-drafts/d2/802-1Qbv-D2-1-dis.pdf. It was also suggested that the following previous contribution could be useful, though no discussion on this contribution occurred and is provided for reference: https://www.ieee802.org/1/files/public/docs2014/bv-admin-parameters-tony-jeffree-1214.pdf. It was agreed that a couple of approaches could be considered here and that further discussion of the options will be needed. One approach is for the internal implementation to adjust the gate controls in accordance with the internal delays caused by clock inaccuracy or different granularity. Another approach is for the implementation to punt this to the management station that creates the schedules and have that station consider a different Tick granularity in a schedule unique for the device. In either case, it would be helpful for the implementation to provide some more information about the accuracy of the clock or delays in responding to Tick events. Further discussion is required at a future meeting and it was suggested to revisit the initial motivation for the current text, use a whiteboard to capture the discussion and to eventually provide specific text for 802.1Q to clarify the solution. Technical experts review
2021-09-24 20 Sep 2021 Interim The group prefers to discuss the item in TSN with a contribution to facility the discussion. The requestor agreed. One solution to consider is to remove the Tick handling from this state machine and create a separate timer state machine the only counts down to zero, at whatever tick granularity it operates at, but reaches zero at the requested amount of ns. The exit condition would be changed to the signal when the timer state machine reached zero. Another approach could be to decrement exit timer by Tick. Currently exit timer is set to timer interval. Alternatively we could change the definition of Tick. It would be preferred to not change the meaning of the managed objects (MIB/YANG) Technical experts review

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