Advice sought on fanning data to several PVs

[Ron Chestnut <rpc@SLAC.Stanford.EDU>]

We use GPIB to access a DVM whose voltage translates into PEP-II total Ring current. Up to now we 
have used only one number, along with the Epics timestamp from the associated PV. We have provided
adequate device support to access the single number of interest.

This DVM is now to be multiplexed for two rings, delivering four doubles on each read: Beam 
Current, Time of reading (ms since some arbitrary 0), Other Beam current, Other time of reading.
We can fetch this data with modified device support (into an internal ascii buffer), but now must 
decide how to get it into four seperate data.

Scenario 1:

Modify the device support for a Waveform (length 4, doubles). Let a subroutine record fan these 4 
items to a seq record, which strobes them into 4 individual soft AI records.

Question: is this overly expensive (at 1 Hz readout)?

Scenario 2:

Have one GPIB-AI record which does the above processing in device support.

Question: Which links can this "master" AI record follow to force updates of the other three?
          What do the Database connections look like?

Scenario 3:

Have one GPIB-AI record which cycles through the 4 values each time the record is processed.

Question: How does one synchronize this kludge?
          What do the Database connections look like?


Thanks in advance for your advice.

/Ron Chestnut
SLAC