FPGA based control system for space instrumentation

Abstract

ABSTRACT The prototype for a general purpose FPGA based control system for space instrumentation is presented, with particular attention to the instrument control application software. The system HW is based on th e LEON3FT processor, which gives the flexibility to configure the chip with only the necessary HW functionalities, from simple logic up to small dedicated processors. The instrument control SW is developed in ANSI C and for time critical (< 10µs) commanding sequences implements an internal instructions sequencer, trig gered via an interrupt service routine based on a HW high priority interrupt. Keywords: instrument control, FPGA, Real Time Applications, Sequencer. 1. INTRODUCTION FPGAs are presently the most suitable devi ces to meet the requiremen ts that characterize the in strument control systems onboard space instrumentation: small size and weight, very low power consumption, radiation tolerance and high reliability. They combine several system functions on a single chip, including microprocessor functionality and small size memory. In particular, in the recent years, the possibility to use FPGAs has given the opportunity to develop fault tolerant processors, usually not available as commercial Hi Rel components. These processors are the result of a great effort of the Space Agencies [1 ] [2] [3] in suppor ting the research and development ac tivities in this challenging area. The fault-tolerant LEON processor system [4] has been developed within this framework. It includes functionality to detect and correct single-event upset (SEU) errors in all on-chip RAM memories and can be used in the harsh space environment. The LEON architecture is based on the SPARC v8 architecture. This processor will be used in several space missions (i.e. the Taiwanese ARGO, the Swedish PRISMA mission, the European Space Agency GAIA and BepiColombo) and it is planned to be used also in a number of medium size missions competing in the frame of the ESA Cosmic Vision program. Several general purpose HW systems have been proposed in recent times [5][6] based on the use of the LEON FT processor on top of different target devices, i.e. Atmel AT607E for Leon2 systems, and ACTEL RTAX FPGA technology for LEON3 systems. In these single board devices the CPU is integrated with several different interfaces (SpaceWire, CAN bus, MIL-STD-1553), to exploit a multipurpo se networking capability, able to meet the requirements coming from different mission scenarios. The aim of this work is to develop a prototype of a generic Instrument Control System to be used in the payload instruments onboard future scientific missions (e.g. the study of the SAFARI Instrument onboard the JAXA-ESA SPICA Mission [7]). We decided therefore to adopt a FPGA-based approach, using the LEON processor as the main system CPU. The generic processor IP core has been customized to include the components reported in Figure 1. A set of baseline functionalities has been defined to be implemented by the prototype, including the possibility to handle, in addition to standard external interfaces, also a SpaceWire link. The work has been focused on the development of a generic Instrument Control Application Software and, in particular, on the need to include in the Control System hard real time capabilities coupled with the possibility to easily reprogram from ground the onboard control procedures. Indeed, standard Operating Systems (OS) and application SoftWares (SW) already available for the selected environment, even when they meet the necessary timing requirements (Real time OS), hardly allow a dynamic programmability of the activities onboard.