The control system for the CMS tracker front end

The compact muon solenoid (CMS) tracker uses complex, programmable embedded electronics for the readout of silicon sensors, for the control of the working point of optical transmitters, for the phase adjustment with respect to the 40-MHz large hadron collider (LHC) clock, and for the monitoring of voltages, currents, and temperatures. To establish reliable low-noise communication with the outside world, the control chain has been designed to operate over a ribbon of digital optical fibers. A small-scale prototype of the control system for the CMS tracker has been recently developed; it is based on a front-end controller unit that distributes, via high-speed digital optical links, both timing signals and slow control data to the clocking and control units where they are fanned out to the front-end electronics. To operate these devices and finally perform the downloading of the settings needed to operate the system, a multilayered software architecture has been developed in such a way that the end user does not need to know any of the details concerning the hardware structure. The parameters relevant to the proper operation of the entire system are stored in an Oracle database; an interface between the slow control software and the database allows one to access and retrieve the values of the parameters that need to be downloaded. This paper describes the components, hardware and software, of the prototype control system developed for the CMS tracker.