1.2.3.6 Immunity to Firm Errors

Firm errors occur most commonly when high-energy neutrons, generated in the atmosphere, strike a configuration cell of an SRAM FPGA. The energy of the collision can change the state of the configuration cell and thus change the logic, routing, or I/O configuration behavior in an unpredictable way.

Another source of radiation-induced firm errors is alpha particles. For alpha radiation to cause a soft or firm error, its source must be in very close proximity to the affected circuit. The alpha source must be in the package molding compound or in the die itself. While low-alpha molding compounds are being used increasingly, this helps reduce but does not entirely eliminate alpha-induced firm errors.

Firm errors are impossible to prevent in SRAM FPGAs. The consequence of this type of error can be a complete system failure. Firm errors do not occur in SmartFusion cSoCs. Once it is programmed, the flash cell configuration element of SmartFusion cSoCs cannot be altered by high energy neutrons and is therefore immune to errors from them. Recoverable (or soft) errors occur in the user data SRAMs of all FPGA devices. These can easily be mitigated by using error detection and correction (EDAC) circuitry built into the FPGA fabric.