Consorzio RFX – Padova, February 7 th 2011 RFX-mod Programme Workshop 2011 – Padova, February 7 th 2011 RFX-mod Programme Workshop 2011 RFX-mod Feedback Control System Upgrade G. Manduchi, A. Barbalace

Consorzio RFX – Padova, February 7 th 2011 Current Control System Architecture MHD Mode ControlPlasma Position ControlToroidal Field Control

Consorzio RFX – Padova, February 7 th 2011 Main Features of the Current System Distributed To account for different location of sensors and actuators; to distribute computing load. Advantages: computing load can be spread among computers. Sensor and actuators can be dislocated around the experiment. Drawbacks: network connections introduce delays in system response. The system must be pipelined to achieves higher throughput. Modular The same basic software used on all nodes; only control algorithms are changed. Advantages: modularity proved to be a successful approach. Drawbacks: a more comprehensive software Framework is required to handle complex systems Configurable Algorithm updates and IO upgrades can be fulfilled by editing a C header file (recompilation is required). Advantages: easy configuration proved to be a key factor in reducing development time Drawbacks: reconfiguration need recompilation.

Consorzio RFX – Padova, February 7 th 2011 Critical Factors Latency Current overall latency is around 1.5 ms (between 3 ÷ 4 sampling periods). This represents a critical factor in quality of control sometimes leading to instabilities. Sampling frequency Current sampling frequency is 2.5 kHz.A higher sampling rate improves the quality of integration/derivation. Computing Power Currently only most significant modes are considered. Operations such as sideband correction and sensor radius extrapolation are highly computing-intensive and require more power Simulation Currently it is not possible to inject a dummy signal to test the control system. The possibility of dry runs of the system, automatically performed before the shot, allows the detection of possible malfunctions which may affect plasma performance and machine integrity.

Consorzio RFX – Padova, February 7 th 2011 New Control System Design from Distributed processing.. switch..to Centralized processing To account for different location of sensors and actuators. Sensors and actuators are still displaced around the system; PCIe Bus Extenders (optical fiber or copper cable) will provide direct connection to the central processing (no Reflective Memory). To distribute computing load.Multicore/processor technology provides all the required computing power; Modularity is retained: the work carried out by the former embedded computer it is now executed by a dedicated processing core. processor switch There is no latency due to data distribution over a network

Consorzio RFX – Padova, February 7 th 2011 New Control System Architecture

Consorzio RFX – Padova, February 7 th 2011 Evaluated Hardware Details We have evaluated National Instruments PXI- 6723; a 13bit multi Digital to Analog converter with 32 analog outputs. Each reference generation node is made up with a PXI rack hosting 3 PXI-6723 boards. Every output is used. Data generation completes after 60us (Intel QPI bus) or after 120us (Intel FSB bus). Data transfer is governed by the processing core via Programmed I/O. We have evaluated National Instruments PXI- 6255; a non simultaneous sampling multiplexed 16bit ADC with 80 analog inputs. Each acquisition node is made up with a PXI rack hosting 3 PXI-6255 boards. Every board is setup to scan 64 channels periodically. A scan completes in 90us and data is ready to the central processing after few microseconds. Data transfer is mastered by the devices via Direct Memory Access (DMA). Data AcquisitionWaveform Generation

Consorzio RFX – Padova, February 7 th 2011 Non Simultaneous Sampling In Real-Time The reconstruction will lead to a quasi exact low-frequency signal and a less precise high frequency signal. The acquisition downgrade to 14bit. Data is filtered via a Fractional Delay FIR implementing Lagrangian interpolation Is it possible to realign the samples? After the Pulse (offline) The reconstruction will lead to a theoretically exact signal. All 16bit could be restored. Data is convolved with a sinc function. Yes, because channels are sampled at known instants. Frequency spectrum of a sample DFLU signal..but multiplexing introduces also settling time issues due to switching between different channels

Consorzio RFX – Padova, February 7 th 2011 Simultaneous Sampling Solutions alternative to evaluated hardware National Instruments Data bus PXI Express (PCIe) in PXI rack; PXIe input channel boards, 16bit; Each 192-channel acquisition node may be implemented with a PXIe-1075 chassis with 12 (18 available) PXIe-6348 boards. Data bus PCI Express in ATCA rack; Custom devel 32 input channelboards, 24bit; Each 192-channel acquisition node may be housed in an ATCA shelf with 6 custom developed ATCA-MIMO-ISOL boards. IST-IPFN Both focus on high data throughput IPFN solution is designed for high availability (five nines)

Consorzio RFX – Padova, February 7 th 2011 New Software Framework What about the previous Framework? The software framework developed and currently used in RFX did a good job. However, it has been developed with a well-defined architecture in mind, so it is not so easily portable to new architectures and platforms. Joint efforts in fusion community gave rise to.. General frameworks for real-time control, notably PCS and MARTe. PCS has been developed at DIII-D and is used in a few machines (e.g. DIII-D, MAST, EAST). MARTe has been developed at JET (by the PPCC group in collaboration also with RFX) and is also used in few machines (e.g. JET, FTU, ISTTOK, COMPASS). MARTe has been chosen!

Consorzio RFX – Padova, February 7 th 2011 New Operating System The current system uses Wind River VxWorks Rugged real-time operating system; Some important bugs in TCP/IP communication; Very expensive. Linux is becoming an interesting candidate for the new system Soft real-time system; Real-time extensions of Linux make it a hard real-time low-latency operating system; Linux’s official RT patches are good enough to make it hard real-time OS We have chosen Linux with its officially released RT patches

Consorzio RFX – Padova, February 7 th 2011 Pipelined Multicore Execution Real time computation for MHD control is carried out in a pipelined organization with three stages: Data Acquisition, Control Computation, and Reference Waveform Generation. New cores can be added to provide additional computation in the case it can be performed in parallel.

Consorzio RFX – Padova, February 7 th 2011 Realtime Performance Prototype running: A simple two stage pipelined I/O cycle developed in MARTe; RedHat Enterprise Linux 5.5 with RT patches from CERN (Scientific Linux Distribution) kernel el5rt; Multicore Intel Xeon processor 2GHz (4 HT cores x86 64bit) QPI bus; 8kHz data acquisition Clock Frequency Prototype setup: A PXI input rack hosting two NI PXI-6255 acquiring 64*2 input channels; A PXI output rack hosting two NI PXI-6723 generating 32*2 output references. Measured Overall latency 150us (average) 200us (WCET)

Consorzio RFX – Padova, February 7 th 2011 Costs Comparison NI Prototype Cost Old System Cost

Consorzio RFX – Padova, February 7 th 2011 Commissioning Plan (1 of 2) Mailstone 1 - Deadline 30 March Test of NI Prototype in RFX Experimental Campaign Objectives This installation will assess the usability of the evaluated hardware for data acquisition (checking cross-talk and cross-channel switching problems). Investigate the possibility of numerical integration (both integrated and non integrated signals will be acquired). Procedure A first prototype system is being installed for acquiring poloidal field values Requirements Front-end duplication Costs All the computing and acquisition components are available in house. –The support computer is recycled (there are no real-time computing to implement on) –The IO boards were used in the prototype Front end boards (i.e. signal splitters) must be designed and made.

Consorzio RFX – Padova, February 7 th 2011 Commissioning Plan (2 of 2) Mailstone 2 - Deadline TO BE DEFINED - MHD Feedback System Commissioning Objectives Run the new MHD Control System in parallel with the current System. The new system will not interfere with RFX operations. Procedure The new system will be installed in parallel to the current one using signal splitters. Requirements Multicore server; IO boards, cabling and racks; Development of few software components. Costs Multicore server; IO boards, cabling and racks; Front end boards (i.e. signal splitters).

Consorzio RFX – Padova, February 7 th 2011 Conclusions The new Feedback Control System of RFX proposes an innovative hardware architecture in Fusion Devices; distributed nodes communicating via a real-time network (ATM, Ethernet, Reflective Memory) moved to multiprocessor cores and communication is achieved on the same RAM via shared memory. COTS solutions for computing (multicore servers) ADC and DAC (PXI-based solutions with bus extenders) proved cost-effective and reliable. Linux is becoming a very good candidate for real-time feedback control systems in fusion devices. MARTe proved to be an extremely flexible environment to develop Hard Real-Time Control Systems. processor switch