PAF BYU Data Acquisition (Stand Alone Operation)

Quick Start Instructions

The following is most conveniently done from a single Windows machine on the 'ad' network, using Remote Desktop if necessary.


Figure 1 - Socket Connections. Dashed lines are transient connections.

This web page is a user's guide to the operation of the BYU CASPER data acquisition system for the NRAO phased array feed (PAF). This data acquisition system consists of the second-generation BYU 40-channel analog receiver, a CASPER 64-channel analog-to-digital converter, a ROACH I CASPER FPGA board, and a Linux host computer with RAID data storage. This system can record high-data-rate complex FFT output spectra or accumulated cross-product spectra from all input channel combinations. At the moment (Feb. 2013) this user interface software supports only the complex FFT recording mode.

The PAF system is designed for use on the GBT and includes the dipole array, cryogenic amplifiers, an L-band fiber optic RF signal transmission system, a frequency conversion and band-limiting analog receiver, and the digital data acquisition back-end. The dipole array, cryogenics and fiber-optic transmitters are in the PAF front-end box. Everything at the other end of optical fibers is in the Jansky Lab "tape room" adjacent to the GBT control room. The front-end box may be at the GBT prime focus, the focus of the 20-meter telescope, or the outdoor test building. There are optical fibers from each of these locations to the "tape room".

The PAF system may be run stand-alone, as when performing tests and calibration in the lab or outdoor test building, or as a GBT receiver/back-end in coordination with telescope control. Figure 1 shows Ethernet socket the connections between the software components of the PAF system. The dashed lines in Figure 1 represent socket messages used to setup the PAF system and initiate data acquisition. The socket messages are described in a separate document (to be attached here). The "BYU Rcvr GUI" is the graphical user interface for stand-alone control and shown in Figure 2. This software module is suplimented by GBT Monitor and Control when used on the telescope.
Figure 2 - GUI for stand-alone control

Two file types are produced by each data acquisition scan: a raw data file on the BYU DAQ system disk and a FITS file that contains all of the hardware setup parameters for that scan. Both data files will use the same date/time string, e.g. 2013_02_04_14:23:45, as the file name so that these two files can be associated for data analysis. The FITS file will be written in the Linux file system. Under GBT control this will always be in the directory /home/gbtdata/[prog name]/RcvrArray1_2/, where [prog name] is the name assigned to the test or observing program by the telescope schedule administrator plus an observing session serial number, e.g., AGBT08B_014_07. In stand-alone mode any accessable directory may be specified in the designated text window on the GUI screen.

Socket Servers

The socket servers each open the receive end of a socket and watch for connections and messages. A server must be opened before any messages are sent to it, but it may be left running for as long as the login to the machine is active. Each server is addressed by message senders by its network address and a unique port number assigned by the code writer. Hence, a message sender must know which machine a server is running on. The network address and port number are specified near the top of each code file, both sender and server. The "Quick Start" instructions at the top of this web page reflects the current state of the code and the machines it runs on.

Server for BYU DAQ System

As shown in Figure 1, the "BYUServerGBT" server, whose code file is, accepts messages from the stand-alone GUI manager or GBT Control system and passes them to the computer that hosts the BYU DAQ system. The DAQ setup parameters are also passed to the FITS file server so that they can be archived in the receiver FITS file associated with every scan

Server for GPIB Instruments

The GPIB server translates socket messages into GPIB instructions for the signal generators that act as local oscillators, ADC clock, and phase monitor tone burst. These instruments are connected to the host PC, "papillon", with a USB to GPIB adapter cable. Typically, the instruments are set once at the beginning of an observing run. The default values set when the server is started should be the correct values for the PAF receivers and data acqusition system. The user only needs to change the sky frequency to the required value.

Server for FITS Writer

The FITS server collates setup information from the GPIB and ADC servers, assembles it into FITS format, and writes this into a new FITS file at the beginning of each data acquisition scan. The FITS file will be written in the Linux file system so this server must run on a Linux machine. Under GBT control this will always be in the directory /home/gbtdata/[prog name]/RcvrArray1_2/. In stand-alone mode any accessable directory may be specified in the designated text window on the GUI screen.