[Sois-tcoa] Time Distribution Service - additional primitives?

[Stuart.Fowell at scisys.co.uk]

Hi guys,

I'm currently doing some modelling work on TCOAS services indirectly for
ESA. Because of the lack of available SOIS specifications at the time of
requirements capture, Astrium have had a go at specifying some themselves,
from which I'm then modelling possible implementations.

As far as Time Distribution is concerned, they have, beyond the
TIME.REQUEST and TIME.INDICATION, the following primitives (in two broad
categories):

1. Use of OBT:

WAIT_FOR_TIME.REQUEST         request to receive notification at a certain
time event
      parameters might include:
            request token
            class of event          absolute or relative time, periodic
event
            value             absoluate time, relative time or period
WAIT_FOR_TIME.INDICATION            indication of the outocme of the
request for notification at a certain time event
TIME_EVENT.INDICATION         indication that time event has occurred
      parameters might include:
            request token

I originally questioned the need for the need for WAIT_FOR_TIME.REQUEST as
this felt like the domain of an RTOS. However, I can see the need for an
event triggered by a timeout associated with the OBT, e.g. a time-tiggered
command.

2. Managing OBT:

SET_TIME.REQUEST              request the modification of the Onboard Time
(OBT).
      parameter:
            time              new OBT
SET_TIME.INDICATION           indication of outcome of request to modify
OBT

CONFIGURE_TIME_SYNC.REQUEST   request to enable/disable
auto-synchronisation
      parameters might include:
            enable/disable
            master                  indicate local clock is the master (or
not)
            protocol          select auto-synchronisation protocol
            period                  period of auto-synchronisation protocol
(this may be fixed for particular implementations/protocols)
CONFIGURE_TIME_SYNC.INDICATION      indication of the outcome of the
configuration of the auto-synchronisation

RESYNCED_TIME.INDICATION      indication that the local OBT has been
modified due to either SET_TIME.REQUEST or auto-synchronisation
      parameter:
            time              new OBT
SYNC_LOST.INDICATION          indication that auto-synchronisation with a
master clock has been lost

Comments?

Stuart

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Stuart D. Fowell
Senior Consultant
SciSys Ltd
Clothier Road
Bristol, BS4 5SS, UK

Tel: +44 (0)117 971 7251
Fax: +44 (0)117 971 1125
Email: stuart.fowell at scisys.co.uk
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