The data collection system is a complex electronics and software system shown in Figure 3. The real-time functions of the system which provide the clock signals for the FPA and A-D converter, and the image acquisition, are performed by a set of boards based on the Motorola 56001 Digital Signal Processor. Most of these boards are shown in the top row of Figure 3. The boards share a custom data bus, the ``Peckbus" designed by Berkeley Camera Engineering of Hayward, CA. The ``metronome" for the system is the ``timing generator". The timing generator emits the digital signals for operating the array pixel, row, and frame shift registers, the pixel reset pulse, and the sample and hold and A-D converter trigger pulses for the preamplifier/A-D system. The ``level shifter" tailors the clock signals for the array to the appropriate analog levels and provides the array voltage biases.
The outputs of the array are amplified and digitized by a new preamplifier/A-D converter described below. The digitized data is accumulated in the coadder boards, one for each array output line, and then sent to the ``pass-through processor". The pass-through processor, another DSP system, controls the data flow, and the chopping secondary mirror.
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The real-time system is governed by a single board SPARC computer (made by Force) on a VME bus, called the ``target". The VME bus is shown in the middle row of the drawing. The target computer receives the data from the camera, and in turn, delivers the data to a disk mounted by the ``host" computer located in the telescope control room. The images written to disk are written in the FITS format and the file header records all pertinent parameters of the data acquisition system and the telescope. Both the host and the target operate under the UNIX operating system, where the key software programs are a set of remote procedure calls (rpc) running on the target computer. The host computer, a Sun Sparc20, communicates with the Keck ``keyword" system through which it can control and monitor all the telescope operations. A ``quick-look" program written for the LWS instrument has been adapted to provide real-time display of the camera images [3]. Processes associated with the host computer are shown in the bottom row of the drawing.
A set of boards [9] on the VME bus provide housekeeping data to the target computer in order to monitor various temperatures within the camera, and the positions of the filter and lens wheels. The motors [10] for driving the wheels are also controlled by the target computer. The entire system is mounted on the IR module and communication between the host and target computers occurs via a 100baseT Ethernet connection. The observer controls the camera by issuing keyword commands from the host computer. A series of observations can be performed by running ``C shell" scripts; for example, collecting a cycle of images through a filter set.
We have modified the software to operate the new Boeing array. During this period extensive testing of the software and hardware took place and we have greatly improved the robustness and efficiency of data collection. Long overnight data sets are now routinely acquired at chopping rates of 10 Hz, with parallel housekeeping and real-time image display processes running; this is a dramatic improvement over earlier IRE systems. The system can acquire data with very high efficiency (>90%) at frame rates of 100 Hz when many frames are coadded. When a ``speckle imaging" mode is used with chopping, image pairs can be recorded to disk at 5 Hz, with a 50% duty cycle; this is a considerable improvement over earlier IRE based systems.