Continuous Data Recording on Fast Real-Time Systems

The PCU-Project [1] launched for the enhancement of the vertical stabilisation system at JET required the design of a new real-time control system with the challenging specifications of 2Gops and a cycle time of 50ms. The RTAI based architecture running on an x86 multi-core processor technology demonstrated to be the best platform for meeting the high requirements. Moreover, on this architecture thanks to the smart allocation of the interrupts it was possible to demonstrate simultaneous data streaming at 50MBs on ethernet while handling a real-time 100kHz interrupt source with a maximum jitter of just 3ms. The RTAI-based PCU-controller, because of the limitations of the 32bit Linux kernel mode address space, o ers a maximum practical data storage of 800MB per pulse. While this can accepted for normal operation it posed some limits in the debugging and commissioning of the system. In order to increase the capability of the data acquisition of the system we have designed a mechanism that allows continuous full bandwidth (56MB/s) data streaming from the real-time task (kernel mode) to either user mode data collector or a potentially an external data acquisition server. The architecture involves a peer to peer mechanisms where the sender running in RTAI kernel mode broadcasts large chunks of data using UDP packets, implemented using the 'fcomm 'RTAI extension [2], to a receiver that will store the data. The paper will present the results of the initial RTAI operating system tests, the design of the streaming architecture and the first experimental results.
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