# Earthworm Modules:
Srusb2ew Overview

(last revised 05 March, 2010)

Introduction
srusb2ew allows the Symmetric Research USBxCH family of low cost 24 bit data acquisition systems to send data to an Earthworm system running either Windows (WinXP/Win7) or Linux. USBxCH models with 4 and 8 channels are supported. Very accurate timestamping of the acquired data results when an optional GPS antenna is used with the USBxCH A/D. Timestamping using the PC system time set by NTP is also available.
srusb2ew reads configuration information like sampling rate and USBxCH model from an Earthworm style .d configuration file and then opens drivers and initializes hardware for the USBxCH and optional GPS antenna. Then it starts the A/D and goes into an infinite loop acquiring data, converting it to Earthworm tracebuf2 format and writing it out to the specified Earthworm ring. On each pass through the loop, it also sends a heartbeat message to the Earthworm ring.
In order to run srusb2ew, you need a working Earthworm system, a USBxCH A/D board, and the USBxCH device driver and library software that comes with the board and is also available free from the Symmetric Research website www.symres.com. For accurate timing information, a GPS antenna is also recommended.
Setup
Follow any instructions given in the official documentation to get Earthworm up and running.
The first step in adding USBxCH data is to install the USBxCH software. This can be done by unpacking the usbw2k.zip or usblnx.tar file and running the included install script to copy the SR software to the \SR\USBXCH directory. Linux users should substitute /usr/local/SR/USBXCH for references to the \SR\USBXCH directory.
You will also need to install the USBxCH device driver. Under Windows, this is done automatically via the Add New Hardware wizard and Plug 'n' Play. Under Linux, use the indriver utility the Driver subdirectory. See the readme file in the \SR\USBXCH\Driver or /usr/local/SR/USBXCH/Driver directory for more information.
Then hook up the A/D hardware. Make sure it is working correctly by running the diagnostic program in the \SR\USBXCH\Utilities\Diag directory. The acquisition programs in the \SR\USBXCH\Scope and \SR\USBXCH\DVM directories can also help in checking out a new system.
To add an (optional but recommended) GPS antenna purchased from Symmetric Research, plug the 2.1mm power connector into the second 2.1mm jack on the back of the USBxCH and plug the DB25 connector on to the 25-pin Dshell digital input connector on the front right side of the USBxCH. Make sure it is working correctly by running the NmeaTime program in the \SR\USBXCH\Utilities\NmeaTime directory which shows the received NMEA strings with the GPS information. When satellite lock is achieved, the red led will begin blinking and the $GPRMC string will show the letter A in the second field instead of the letter V.
Once Earthworm and the USBxCH are working on their own, it's time to get them working together. Edit the srusb2ew.d configuration file settings so they are appropriate for your system.
At this time, you will probably also want to edit some additional Earthworm module configuration files to handle the USBxCH data that will be coming. This might include adding tanks for the USBxCH data in wave_serverV.d if the data is to be saved on the same computer or setting the USBxCH channels in export_scn.d if the data is to be exported to another computer.
In the beginning, it is probably best to use two separate command prompt windows. In the first, run startstop to start Earthworm. In the second, type "srusb2ew srusb2ew.d" without the quotes to start the USBxCH acquiring and sending data.
You can check the log files and run diagnostic programs like sniffring and sniffwave to help diagnose any problems. If something isn't going right, it is easy to stop srusb2ew, modify its configuration file, and restart it without having to stop the rest of Earthworm. Once you've got your parameters set right, then go ahead and have startstop control srusb2ew too.
Compiling
srusb2ew is written in C and is compiled and linked using the standard Earthworm makefiles such as makefile.nt. In order to successfully compile, access to the USBxCH system software is required. This software, including source, is included with every USBxCH purchase. It is also available for free download from the Symmetric Research website www.symres.com.
All Symmetric Research software, including the USBxCH system software and srusb2ew, has been designed so a single set of source code can service different operating systems. This is accomplished primarily through the use of conditional compilation which selects OS specific code at compile time based on which SROS_xxx setting is defined. Valid options include SROS_WIN2K (for both Windows 2000 and XP) and SROS_LINUX. Solaris is not available.
More Info
General questions about Earthworm are probably best answered by the official Earthworm User's discussion group. But, if you have specific questions about srusb2ew and its configuration parameters, please let us know at info@symres.com.

Module Index | Srusb2ew Commands