ar X iv : p hy si cs / 0 11 11 66 22 N ov 2 00 1 THAP 003 REMOTE DEVICE ACCESS IN THE NEW CERN ACCELERATOR CONTROLS MIDDLEWARE

This paper presents the Remote Device Access (RDA) package developed atCERNintheframework of the joint PS/SL Controls Middleware project. The package design reflects the Accelerator Device Model inwhichdevices,namedentitiesinthecontrolsystem, canbecontrolledviaproperties.RDAimplementsthis model in a distributed environment with devices residinginserversthatcanrunanywhereinthecontrols network. It provides a location-independent and reliable access to the devices from control programs. By invoking the device access methods, clients can read,writeandsubscribetodevicepropertyvalues.We describe the architecture and design of RDA, its API, and CORBA-based implementations in Java and C++. First applications of RDA in the CERN accelerator controlsystemsaredescribedaswell. 11INTRODUCTION In 1999 an initiative was launched to create a commonsoftwarecommunicationinfrastructureforthe CERN accelerator controls. This infrastructure should replace existing heterogeneous software protocols and componentsandprovidenewfacilitiesfortheLHCera, inparticular: • SupportthestandardAcceleratorDeviceModel anddeviceI/Oservices[1]. • Support the publish/subscribe paradigm and synchronization of application programs with AcceleratorTiming. • Provide inter-operabilitysolutionsforindustrial controlsystems. Ithasalsobeenrequestedtouseavailablestandards andcommercialproducts.Basedontheserequests,the ControlsMiddleware(CMW)project[2]waslaunched. Following the technology study and the requirements capture, the middleware technology was selected and the base architecture proposed. A number of software components implementing the proposed architecture were developed; one of them is the RDA package, which provides access to the accelerator devices from application programs in a distributed heterogeneous environment. 22DESIGNCHOICES Besidesthealreadymentionedgeneralrequirements, thedesignofRDAwassignificantlyinfluencedbythe need to provide multi-language and multi-platform inter-operability. RDA should act as a " software bus " that transparently interconnects applications and devicesimplementedindifferentlanguages(Java,C++, C)andrunningonanyoftheplatformsusedinCERN accelerator controls (Linux, HP-UX, LynxOS, Windows). The choice of CORBA as a communication technology looks obvious in this situation. It was decided,however,torestrictitsusetotheRDAinternal software.AllCORBAinterfaceanddatadefinitionsare hidden in the package and do not appear in the RDA applicationprogramminginterface(API). Ithasbeendiscussedforalongtimewhetherawide or narrow API would be moreappropriate.WideAPI (different calls for different classes) would expose CORBA to our users and allow them to define device classesanddevice-specificdatatypesinCORBAIDL.