# FieldSystemInterface — Overview

## Description

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The FieldSystemInterface is an EDD service that bridges the telescope Field System software
and the EDD stack. The Field System controls the DBBC (Digital Base Band Converter) hardware
and the Mark5b recorder via dedicated TCP ports. This service translates Field System
commands into KATCP sensor updates visible to the EDD Master Controller, and gates VDIF
recording in the VDIFPacker by writing to its POSIX message queue.

Because it needs to be reachable at all times during an observation session, it runs as a
persistent service that starts automatically at provision time and restarts on failure.
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## Responsibilities

- Connect to the DBBC hardware on its control port and expose its state as KATCP sensors
- Connect to the Mark5b recorder on its control port
- Forward configuration (IF/BBC frequency, attenuation) from the Field System to EDD sensors
- Gate VDIFPacker recording by writing to `mq_control`
- Provide the Master Controller with telescope and receiver state

## Operational Context

| Item | Value |
|---|---|
| Type | Always-running service |
| Upstream | Field System software (telescope control) |
| Downstream | EDD Master Controller, VDIFPacker (via message queue) |
| KATCP port | `fs_interface_port` (default 7150) |
| Container image | `field_system_interface` |
| Ansible role | `roles/field_system_interface/` |
| Registered with Master Controller | No (`register_as_pipeline: False`) |
| Launch at provision | Yes (`launch_on_deploy: True`) |
| Restart policy | `on-failure` |