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The purpose of environment store (EnvStore) is to keep records of all transitions so that they can be retrieved later using the timestamp of an event. There are three types of EnvStore:

• epics
• scan
• step (*special envstore for keeping beginstep evt - is not part of detnames in config.software)
• scan 

Storing Variable Names

For 'epics' and 'scan', to be able to access the value quickly, the structure (d.detname[seg_id].alg.var_name) that we learn from configs is stored in a dictionary as:

...

This is done by first locating alg and segment_id that store this variable then matching dgram(s) in the EnvStore is retrieved by searching with timestamp. We then get the value from dgram.epics.alg[segment_id].var_name.

* Special EnvStore: 'step'

Envstore 'step' is there to keep all beginstep events so that we can look them up after. There's not associated detector and interfaces for this type of EnvStore.