[evla-sw-discuss] setting gains on the station board

[Sonja Vrcic]

Please disregard my previous message, I accidentaly prresed 'send' before the message was 
complete. See my comments below.
Sonja


Ken Sowinski wrote:
> Getting the station board gains, especially the requantizer gain,
> right will be important for the three bit samplers.  I talked with
> Bruce about this yesterday and summarize are conclusions and questions
> here.
>
> 2.  We must decide how to communicate to the statino board when and how
> to do this.  The obvious solution is for the executor to send a VCI
> 'modify' document specifiying when to begin the adjustment, and what
> to do.  In addition to an activation time one might want to include
> set points, integration time and, perhaps, desired ALC strategy.
> this depends on implenting the VCI modify funtion.  Is there any need
> for an alternate path which might be available sooner?


 From the point of view of CM this should not be difficult to implement. Most work will be 
implemented on CMIB. CM would simply pass instructions to Station Boards. To speed up 
implementation it is important to define requirements.


Here is my attempt to capture requirements (based on requirements for the Filter Gain 
panel in Station Board GUI):

1. Target filter gain (and other related parameters) to be specified (and set) for each 
subband independently, i.e. for each subband of each baseband pair (or baseband singleton).
2. Parameters are specified per subband and apply for all the antennas (stations) in a 
subarray (as VCI "modify subarray").
3. Alternatively, as for other parameters, user can specify a subset of antennas 
(stations) to be configured.
4. Activation time assigned per subarray (in the same fashion as when creating a new 
subarray).

List of parameters that can be specified for each subband of each baseband:
a. Desired RMS (mandatory)
b. Desired RMS for re-qunatizer (mandatory)
c. Number of integrations (for power measurements) to be used to calculate RMS (optional, 
if not explicitly specified = 100)
d. Number of integrations to discard between the measurements for different stages 
(optional, if not specified it is ON, number of integrations to discard=100). GUI allows 
user to turn this on/off and to specify number of integrations. That was required in 
experimental phases. Is there a need to keep this as externally specified parameter(s) or 
should it be hard-coded in CMIB software ?

Then there is a question of units: in GUI, one can select whether RMS is displayed in 
computer units or normalized units. Which one should be used in VCI. Is there a need to 
implement both options. If possible, it would be nice to simplify interface and 
implementation.

This is just the first attempt, please modify the list as needed.

Sonja

-------------------------------------------------------------------------------------
Here is a copy of the "user help window" for the Station Board GUI - Filter Gain.

Commands:
Refresh reads from hardware and displays:
Filter ID and status
Station/Baseband/Subband IDs inserted in the output data stream (subband)
RFI Detect Level
Scales for used filter stages and for re-quantizer
Number of bits for re-quantizer

Set RFI detect level sets RFI detection level in the filter FPGAs (as specified in the table)

Measure RMS calculates RMS based on the power counts

Adjust filter scales to get desired RMS optimizes RMS as close as possible to the desired 
RMS (specified by user)  RMS is calculated as follows:
RMS = sqrt(powerNdOn + NdOff) / numberOfIntegrations)
  Use normalization units applies to RMS. If selected, RMS is normalized:
normRMS = (RMS / (2^(numberOfBits - 1) - 1))
  For stages 1 to 4, numberOfBits = 16. For re-quantizer, number of bits is obtained from 
the Filter FPGAs (and displayed in the table).

Save/Load Configuration to/from File on the "Main" menubar allows you to optionally save 
or load "RFI Detect Level" (column RFI) and "Desired RMS" (columns D_RMS and D_RQ_RMS). 
Only the filters with their "Select" box checkmarked will be saved.
When loading, the "Select" checkbox will be used to indicate which filters were updated.

RMS Units:
RMS displayed in computer units can be converted to normalized units. Conversion from 
normalized units to computer units is not performed. If "Use normalization units" not 
selected, columns for measured RMS are filled with blanks, and desired RMS is set to the 
default values.

RMS is calculated for the stages that are used (see the Filter GUI's "Format" box, Primary 
Signal) and for the re-quantizer.

When the Start button is clicked, the following is performed:
Get filter status, scales and number of bits for re-quantizer;
For each stage {
     Configure all the (green) filters for stageX;
     Collect power counts (for all the filters);
     For each filter {
         Calculate RMS;
         Display RMS;
         If (adjustScales is selected) {
             Calculate new scale;
             Configure filter for the new scale;
         }
     }
     If (adjustScales is selected) {
         Collect power counts (for all the filters);
         For each filter {
             Calculate RMS;
             Display RMS;
         }
     }
}

Get RFI and scales from hardware;
Number of power counts integrations used to calculate RMS:
User can specify the number of power count integrations used to calculate RMS.
By default, this number is the same as the power count integration factor obtained from 
hardware; which means that, by default, one report (table) is used to calculate RMS.

Delay between stages:
RMS is calculated for one stage at a time. Before calculating RMS for each stage, filter 
configuration is slightly modified. To ensure that the power counts used to calculate RMS 
are only for the data processed after the configuration change, the power counts received 
immediately after the filter configuration change should be discarded.  By default, the 
number of integrations to be discarded is the same as the power counts integration factor 
set in hardware; which means that the first report (table) received after the 
configuration change will be discarded. This feature can be disabled.

-------------------------------------------------------------------------------------------







>
> 3.  We must decide how the executor knows when to tell the correlator
> to set gains.  Is it explicitly in the scripts?  Should the executor
> understand enough about the meaning of the script to discern when to
> send the cause a gain setting?  Getting this right will interact with
> setting up the antenna, setting downconverter gains, and antenna motion.
>
> _______________________________________________
> evla-sw-discuss mailing list
> evla-sw-discuss at listmgr.cv.nrao.edu
> http://listmgr.cv.nrao.edu/mailman/listinfo/evla-sw-discuss

-- 
Sonja Vrcic
Software Engineer
National Research Council
Herzberg Institute of Astrophysics
Penticton, BC, Canada
Tel: 250-497-2309 / 250-497-2300
Sonja.Vrcic at nrc.gc.ca
http://www.nrc-cnrc.gc.ca/eng/ibp/hia.html