DAQ programs

The DAQ programs needed for the COMPASS experiment can be grouped into three categories:

• Software for frontend processors managing the collection of data from the detector readout electronics and memory management will be probably self-written and tailored to the architecture of the experiment.
• The DAQ machine serves (in the concept presented in the proposal) as eventbuilder and online filter. This multiprocessor system will have a standard UNIX operating system and programs and algorithms specific to the various physics runs of COMPASS.
  Alternatively to eventbuilding in the DAQ machine the possibility of using ATM as transfer protocol to let the data organize itself by the routing mechanism should be studied. This scheme has been investigated by RD31 and would profit from the experience and cost efficiency of ATM achieved in the commercial sector.
• Run control, slow control and calibration will be provided by a system of CPUs mounted in the frontend crates connected to few workstations providing storage, user interfaces and tools for software development. These rack mounted CPUs would profit from a UNIX-like real-time operating system like Lynx.

CERN offers as a general purpose DAQ the product CASCADE. This system ran originally under OS9 and has been ported in large part to run under Lynx-OS, as well. Under Lynx, versions exist to run on single board computers based on the 68K and Power-PC families of microprocessors.

Under Lynx, the first indications are that, to obtain maximum performance, the product would have to rewritten to replace a heavy dependence on signals for interprocess communication with a multiprocessing design based on threads. This would require manpower and a commitment to CASCADE for the future: an unclear situation but one which CMS interest may fuel.

In any case, it is unlikely that CASCADE would be appropriate at the moment to a DAQ requiring a very high bandwidth transfer of data, although tests in collaboration with RD24 have taken place, and high-performance network interfaces (FDL and SCI) have been incorporated in its framework. If at all used in COMPASS, CASCADE could be adapted for the monitor/event control function of the COMPASS DAQ, with the event-building being done largely in hardware or within the DAQ machine.

However it was understood, that an extension of CASCADE support by the ECP division beyond currently running experiments and testbeams is not planned.

It is clear that experience gained in the implementation of CASCADE (especially in its involvement with RD24) and the realization of high rate experiments such as NA48 will be invaluable in the COMPASS implementation.