Reimplement `records.` to allow creating arbitrary records in IOC instance yaml

[GDYendell]

iocbuilder does this parsing dbd files. See dbd.py and recordbase.py for a start.

Acceptance Criteria

• Simple records can be created in IOC instance yaml - e.g. ai, ao, bi, bo, calc, calcout

[gilesknap]

Simple Way to do this

Here's a super easy way to add this feature and make it infinitely flexible:

entities:

  - type: epics.AddToDatabase
    value:-
      record(bo, "BL04I-EA-IOC-01:GTIM_RESET") {
      field(DESC, "Gen Time Error Reset")
      field(DTYP, "General Time")
      field(OUT,  "@RSTERRCNT")
      field(ZNAM, "Reset")
      field(ONAM, "Reset")
      }

Pros

• We could implement this in ibek-support/_global/epics.ibek.support.yaml with no code changes required to ibek
• It can support any type of additional records
• We could still quite easily write a converter from UserIO and record.
• Is a little bit easier than just adding a DB file in the config folder and then adding epics.StartupCommand that calls dbLoadRecords (only a little easier - but also more compatible with the converter than that approach)

Cons

• no checking until runtime failure loading the IOC
• miss other benefits of using YAML to define the fields such as making repeating patterns of records DRY using anchors and aliases

[GDYendell]

I have gotten my use case working with an extra db file. This seems clunky:

  - type: epics.StartupCommand
    command: dbLoadRecords("/epics/ioc/config/extra.db")

Could ibek just automatically load any .db files in config/?

[gilesknap]

it could - that feels a little magic though. I can't think of a good reason to put a db in that you don't want to load. But someone will come up with one eventually.

[gilesknap]

I think we just about concluded that re-implementing xmlbuilder records.xxx was the way to go - there was just some difficulty over which dbd to use to generate the set of knows record types.