[evla-sw-discuss] net sideband and VCI documents

[David Harland]

Is there a consensus on this topic?

Snippets from Ken's email relevant to model2script's production of VCI:
> model2script now generates scripts which use different correlator
> setups for two scans which differ only in net sideband.
> model2script...must recognize that net sideband change does not require a new VCI document
If there is agreement that m2s should not send a new msg when only the 
sideband changes then the sideband information in that msg must be 
unneeded. If that is the case the best thing to do would be to eliminate 
the sideband attribute of the BbParams element of the VCI spec.


Bruce Rowen wrote:
> On a related note, keep in mind that the original reason that the net  
> sideband was presented to the correlator through the delay models was  
> that at that time, the configuration manager (CM) did not exist. The  
> correlator internally pulls net sideband information from the delay  
> model and 'rebroadcasts' this information to itself as if it arrived  
> from the CM. This mode of operation means that as soon as new net  
> sideband information arrives in a delay model, it is rebroadcast and   
> acted upon after about 5 seconds. If it arrived within a CM  
> configuration, it would activate synchronously with the correlator  
> configuration.
>
> On Jun 9, 2010, at 8:53 AM, Ken Sowinski wrote:
>
>   
>> Currently net sideband is conveyed from the executor in three
>> ways, 1) in the delay packets sent to the station boards,
>> 2) in the multicast 'observe' xml document and 3) in the VCI
>> document which is sent in full to configuration mapper and
>> in part to mcaf.
>>
>> Net sideband is needed in the station boards for the phase
>> calculations and to set the sideband flippers, and in mcaf
>> to assign 'sky' frequency to spectral windows.  Net sideband
>> is not used by configuration mapper, it is passed to the station
>> bpards where it is ignored in favor of the information in the
>> delay packet.  The CBE need not know about net sideband because
>> we guarantee, by use of the sideband flippers, that all correlated
>> data is net upper sideband.
>>
>> model2script now generates scripts which use different correlator
>> setups for two scans which differ only in net sideband.  We require
>> this because mcaf examines a truncated VCI document to learn net
>> sideband, but a side effect is the long time it takes to needelssly
>> confiugure the correlator.  Recently this has restricted the choice
>> of programs that are in the observable pool.
>>
>> I suggest that mcaf be changed to use net sideband as transmitted
>> in the 'observe' document, which it already must examined to learn
>> the signed sum of the LOs.  If this is done, then successive scans
>> which use the correlator identically, but change net sideband will
>> not result in reconfiguring the correlator.
>>
>> model2script will have to change to take advantage of this.  It
>> must recognize that net sideband change does not require a new VCI
>> document; and must be sure to not needlessly change the use of
>> Widar subbands when changing band.
>>
>>
>>
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