“The LEON3FT-RTAX Processor Family and SEU Test Results”
The fault tolerant LEON3 processor in combination with the radiation tolerant ACTEL RTAX2000S FPGA presents an alternative to the processors currently used by the space industry. The processor is offered in standard configurations suitable for spacecraft and payload control applications. The standard configurations includes the LEON3FT processor core with associated IEEE-754 floating-point unit, two SpaceWire links, two MIL-STD-1553 BRM, two CAN-2.0 interfaces, memory controller with ECC, timer unit, two UARTs and 16-bit GPIO port. To fit within the resources of a single RTAX2000S, five application-specific sub-set configurations have been defined. These configurations are available as pre-programmed AX2000/RTAX2000S parts in both commercial and high-rel quality levels.
To confirm the SEU tolerance of the LEON3FT-RTAX processor, the RTAX2000S part was submitted to Cf-252 heavy-ion error injection. The error injection lasted for 168 hours, with a heavy-ion flux of 22 particles/s/cm2 at the device surface. A total of 2,429 SEU errors were registered in the on-chip block RAMs. All errors were detected and corrected by the LEON3FT fault-tolerance logic. No anomalies or computational errors were observed. The effective SEU rate was measured to 0.25 errors/minute.
Simulated error injection using the LEON3FT debug interface was performed and correlated with the Cf-252 SEU test data. It was then possible to determine the Cf-252 SEU cross-section for an RTAX2000S block RAM bit to 2.3E-9 cm2/bit. This value correlates well with earlier cross-section measurement performed by Actel at the BNL and TAMU cyclotron facilities, confirming the validity of the Cf-252 test methodology and obtained results.
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