The USB-based Sweeper Magnet data acquisition is built around the VM-USB (VME) and CC-USB (CAMAC) crate controllers available from Wiener Electronics, according the methods defined in the NSCL DAQ software package nscldaq11.x. These controllers contain at their core an FPGA on which the controller firmware is loaded. The controllers have two modes of operation:

1. Interactive mode: commands sent to the USB port are immediately executed and their result returned
2. Data acquisition mode: the controller executes a list of commands preloaded in a stack upon a trigger condition (event, interrupt or periodic)

The first mode is typically used when setting up the modules contained in the crate, such as gains, thresholds and so on, while the second mode is used for acquiring event-driven data. The two modes are mutually exclusive, and issuing an interactive command while in data acquisition mode will typically result in an error or lockup of the controller.

The USB DAQ is a Tcl-based software. It is capable of handling multiple crate controllers (CC-USB or VM-USB) connected to the same computer. The data streams coming from the various crates are synchronized and combined into a single stream by the Sweeper Event Builder (EVB). (Details about the format of the data stream from the Sweeper EVB can be found here).

The time-ordered data from the Sweeper EVB is sent to the ring buffer sweeper, which can then be read by users via analyzer (e.g. SpecTcl, ROOT, etc.). In order to facilitate the parsing of data from the Sweeper, a pre-unpacker software packet was created to organize data from electronics modules (detectors) into C++ structures. Users can couple this pre-unpacker into their analysis software. More details about the Sweeper pre-unpacker software can be found here.