# Earthworm Modules:
Naqs2ew Overview

(last revised August 6, 2000)

Naqs2ew is an interface through which waveform data collected by the Nanometrics data acquisition software, NaqsServer, can be fed into an Earthworm system in near-real-time. Naqs2ew is a client of NaqsServer's "Online Data Streams" service which allows client programs to open a socket connection, subscribe to only the data they want, and receive the requested data over the same socket. The "online data streams" protocol and data formats are described in the Nanometrics Reference Manuals. Currently the only NaqsServer packet types that naqs2ew can process are: channel list messages, decompressed data packets, compressed data packets, and error messages. Naqs2ew is not required to run on the same computer as NaqsServer.

Naqs2ew is a single-threaded program. After reading its configuration file, allocating working buffers, and attaching to a transport ring, naqs2ew attempts to open a socket connection to NaqsServer, using a timeout of CONNECT_TIMEOUT seconds (currently 5 s). If the connection attempt fails, naqs2ew will attempt to connect every CONNECT_RETRY_DT seconds (currently 10 sec) forever. Naqs2ew will continue beating its own heart while trying to establish a NaqsServer connection.

Once it establishs a socket connection with NaqsServer, naqs2ew initiates the "online data streams" protocol. It sends a "connect message," reads and logs the list of available channels, and requests only the channels listed in its own configuration file. If some channels in the configuration file are not available, naqs2ew logs that fact and continues. While the socket connection remains open, naqs2ew reads a complete packet (blocking), converts it to one or more Earthworm TYPE_TRACEBUF messages, and writes the message(s) to the transport ring. Naqs2ew makes no attempt to reorder timeseries packets. It does attempt to produce one-second TYPE_TRACEBUF messages for each channel, buffering any fractional seconds between packets from NaqsServer if necessary. Time tears between packets will cause naqs2ew to produce TYPE_TRACEBUF packets shorter than one-second long. Naqs2ew also logs any error messages it receives from NaqsServer. After each packet is processed, naqs2ew enters its heartbeat function, and issues a heartbeat if its heartbeat timer has expired.

If naqs2ew experiences any socket errors or if NaqsServer breaks the connection, naqs2ew closes the socket and issues a TYPE_ERROR message stating the reason the connection was dropped. It then goes back to looping on reconnection attempts. When the connection is reestablished, naqs2ew will issue another TYPE_ERROR message (really an "un-error" message), stating that everything's OK again.

Module Index | naqs2ew Commands