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- a RetDef object, which defines the CCSDS APIDS and timespans to be retrieved, as well as the "spacecraft ID" of the entity that originated the data, and the root
- a source id (which defines the entity which created the CCSDS data)
- a disk location for the root of the raw-packet archive,.
- a user-specified function obeying the "valcb_t" prototype to receive the event and context data
- a pointer to a user-defined argument to the callback function
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