Add some documentation on data streaming topics and their contents

Author: rerpha

doc/specific_iocs/dae/Datastreaming.md

@@ -25,6 +25,7 @@ Part of our in-kind contribution to datastreaming is to test the system in produ
 
 ![](ISISDSLayout.png)
 
+{#kafkacluster}
 ## The Kafka Cluster
 
 There is a Kafka cluster at `livedata.isis.cclrc.ac.uk`. Port 31092 is used for the primary Kafka broker. 

doc/specific_iocs/dae/datastreaming/Datastreaming---Sample-Environment.md

@@ -2,6 +2,7 @@
 
 All IBEX instruments are currently forwarding their sample environment PVs into Kafka. This is done in two parts:
 
+{#bskafka}
 ## BlockserverToKafka
 
 This is a Python process that runs on each NDX (see code [here](https://github.com/ISISComputingGroup/EPICS-inst_servers/tree/master/BlockServerToKafka)) it monitors the blockserver config PVs and any time the config changes it pushes a new configuration to the forwarder, via a Kafka topic `forwarder_config`. This is a process written and managed by IBEX developers.

doc/specific_iocs/dae/datastreaming/Datastreaming-Topics.md

@@ -0,0 +1,72 @@
+# Data streaming topics
+
+We have a number of topics per-instrument on `livedata`, the {ref}`Kafka cluster<kafkacluster>` we use. 
+
+## `_runInfo`
+
+This contains run start and run stop flatbuffers blobs. 
+
+Flatbuffers schemas in this topic: 
+- [`pl72` - Run start](https://github.com/ess-dmsc/streaming-data-types/blob/master/schemas/pl72_run_start.fbs)
+- [`6s4t` - Run stop](https://github.com/ess-dmsc/streaming-data-types/blob/master/schemas/6s4t_run_stop.fbs)
+
+## `_events`
+
+This contains data from event-mode events.
+
+Flatbuffers schemas in this topic:
+- [`ev44` - Events](https://github.com/ess-dmsc/streaming-data-types/blob/master/schemas/ev44_events.fbs)
+
+{#topics_sampleenv}
+## `_sampleEnv`
+
+This contains sample environment data forwarded from EPICS.
+In a `.nxs` file this should end up in `raw_data_1/selog/`
+
+Flatbuffers schemas in this topic: 
+- [`f144` - All CA and Scalar PVA data](https://github.com/ess-dmsc/streaming-data-types/blob/master/schemas/f144_logdata.fbs)
+- [`se00` - PVA Arrays](https://github.com/ess-dmsc/streaming-data-types/blob/master/schemas/se00_data.fbs)
+- [`al00` - EPICS alarms](https://github.com/ess-dmsc/streaming-data-types/blob/master/schemas/al00_alarm.fbs)
+- [`ep01` - EPICS connection status](https://github.com/ess-dmsc/streaming-data-types/blob/master/schemas/ep01_epics_connection.fbs)
+- [`un00` - EPICS units](https://github.com/ess-dmsc/streaming-data-types/blob/master/schemas/un00_units.fbs)
+
+## `_runLog`
+
+This contains run metadata forwarded from the ICP. 
+In a `.nxs` file this should end up in `raw_data_1/runlog/`
+
+Schemas in this topic match the ones in {ref}`topics_sampleenv`
+
+## `_monitorHistograms`
+
+This contains monitor histograms.
+Flatbuffers schemas in this topic: 
+- [`hs01` - Histograms](https://github.com/ess-dmsc/streaming-data-types/blob/master/schemas/hs01_event_histogram.fbs)
+
+## `_detSpecMap`
+
+This contains details of the detector-spectrum mapping.
+Flatbuffers schemas in this topic: 
+- [`df12` - Detector-spectrum mapping](https://github.com/ess-dmsc/streaming-data-types/blob/master/schemas/df12_det_spec_map.fbs)
+
+## `_areaDetector`
+
+This is raw `areaDetector` data. It's sent by [this line in `ISISDAE`](https://github.com/ISISComputingGroup/EPICS-ioc/blob/716aada58c972cf0661ab6cebc41fba34d29b806/ISISDAE/iocBoot/iocISISDAE-IOC-01/liveview.cmd#L8)
+
+## `_forwarderConfig`
+
+This is the forwarder configuration, sent by {ref}`bskafka`.
+Flatbuffers schemas in this topic: 
+- [`fc00` - Forwarder configuration](https://github.com/ess-dmsc/streaming-data-types/blob/master/schemas/fc00_forwarder_config.fbs)
+
+## `_forwarderStatus`
+
+This is the forwarder status topic which contains details about what PVs the forwarder is forwarding. 
+Flatbuffers schemas in this topic: 
+- [`x5f2` - General status](https://github.com/ess-dmsc/streaming-data-types/blob/master/schemas/x5f2_status.fbs)
+
+## `_forwarderStorage`
+
+This is the last known forwarder configuration, sent by {ref}`bskafka`. This is for if the forwarder crashes, then it can quickly retrieve its last configuration.
+Flatbuffers schemas in this topic: 
+- [`fc00` - Forwarder Configuration](https://github.com/ess-dmsc/streaming-data-types/blob/master/schemas/fc00_forwarder_config.fbs)