A Software Flamework to Control a Network-connected Equipment as a Pseudo Device

Recently network-connected measurement instruments and controllers have increased. Today, Ethernet could be understood as a kind of a field bus for the front-end subsystems. The network-connected equipment uses the socket communication as a common software interface. The socket interface requires different handling from bus attached device access, that is, control application programmers have to understand the socket communication protocol in detail. It is inconvenient for them to develop the software efficiently. We developed a software framework, Device Masquerade, which handles a network-connected device as a pseudo device. The socket interface can be controlled through common equipment access libraries like bus-attached devices. The Device Masquerade consists of three parts; 1) API functions to access pseudo device, 2) a communication client software to access the server running on the remote equipment, 3) a pseudo device driver to interconnect between application programs linking the API library and the communication client. The pseudo device driver implements the exclusive access control. It is possible to replace the socket with other protocol. We applied the Device Masquerade for the installation of motor control units in the linac control system. INTRODUCTION The measurement instruments and controllers with network interface have increased in the field of accelerator and radiation research. Ethernet is recognized as a field bus for the front-end subsystem that provides high-speed communication. IP protocol is popular and implemented as an external communication interface of various control systems. We needed a new software framework in order to introduce the network-connected equipment in the SPring-8 standard software framework [1], MADOCA, (Message And Database Oriented Control Architecture). The software framework handles network communication in the same manner as bus-attached devices. Equipment experts develop application. Understanding the details of the network protocols is inconvenient. In the MADOCA framework, software processes control the same devices at the same time. So we need exclusive access control to the device. It seems that many measurement instruments and controllers with network connectivity are designed to be controlled via a single software process. It is important to implement exclusive access control in the MADOCA framework. We developed a new software framework, named Device Masquerade, to control network-connected devices as pseudo devices. The Device Masquerade uses UNIX device files, so that it can be adapted not only to the MADOCA but also to other control frameworks. This paper reports the design and performance of the new software framework, and explains about an application to the motor control units (MCU) in the linac control system [2]. DESIGN In order to control the network-connected equipment in the MADOCA framework, our requirements were as follows. • It can control network-connected equipment in the same handling as bus-attached devices. • It implements the exclusive access control. • It is a general-purpose software framework. To meet these requirements, we designed the Device Masquerade as follows. • Introduce a client process named Communication client (ComC) to be responsible for communication with a network-connected device. Encapsulates the differences of the networkconnected devices in the ComC. • Introduce Universal Pseudo Device (UPD) to hide the network-connected device from the application programs. • Implement exclusive access control with lock/unlock mechanism in the UPD. • Communicate between application programs and the ComC with the UPD by passing the control messages. Figure 1 shows the schema of the Device Masquerade. Universal Pseudo Device (UPD) Application program Comunication Client (ComC) /dev/upd00 /dev/comc00 network-connected equipment ex) motor controller, encoder, etc. (socket server) IP protocol handling API kernel space user space Figure 1: Schema of the Device Masquerade Proceedings of ICALEPCS2003, Gyeongju, Korea