A resilient, flash-free soft error mitigation concept for the CBM-ToF read-out chain via GBT-SCA

The ToF detector read-out chain of the upcoming CBM experiment at FAIR will be equipped with FPGA-based read-out boards (ROBs), which are going to be operated in a radiation environment. Flash-based FPGAs are not an option for this experiment due to their low total ionizing dose limit compared to SRAM-based FPGAs, and therefore the latter is foreseen for the ROBs. Consequently, precautions against soft errors in the configuration memories of the FPGAs need to be taken to keep the chain operational. The proposed approach merges on-chip single upset correction with external intervention for multiple-bit upsets and resets. The external intervention is going to be implemented via the control path of the chain through the GBT-SCA, which offers a JTAG interface, as well as interrupt-capable GPIOs among other features. Thus, the use of the GBT-SCA enables an event-driven configuration upset mitigation concept, while being itself radiation hardened by design. Conventional blind configuration scrubbing would cause a continuous load on the control path, while the selective frame scrubbing reduces this load significantly. The concept has been validated in beamtests conducted at COSY, FZ Juelich, Germany. The concept, the beamtest results and limitations of the implementation are presented and discussed in this paper.