9.3. User Mode Error Detection
In user mode, the contents of the configured CRAM bits may be affected by soft errors. These soft errors, which are caused by an ionizing particle, are not common in Altera devices. However, high-reliability applications that require the device to operate error-free may require that your designs account for these errors.
You can enable the error detection circuitry to detect soft errors. Each data frame stored in the CRAM contains a 32-bit precomputed CRC value. When this feature is enabled, the error detection circuitry continuously computes a 32-bit CRC value for each frame in the CRAM and compares the CRC value against the precomputed value.
- If the CRC values match, the 32-bit CRC signature in the syndrome register is set to zero to indicate that no error is detected.
- Otherwise, the resulting 32-bit CRC signature in the syndrome register is non-zero to indicate a CRC error. The CRC_ERROR pin is pulled high, and the error type and location are identified.
Within a frame, the error detection circuitry can detect all single-, double-, triple-, quadruple-, and quintuple-bit errors. When a single-bit or double-adjacent error is detected, the error detection circuitry reports the bit location and determines the error type for single-bit and double-adjacent errors. The probability of other error patterns is very low and the reporting of bit location is not guaranteed. The probability of more than five CRAM bits being flipped by soft errors is very low. In general, the probability of detection for all error patterns is 99.9999%. The process of error detection continues until the device is reset by setting the nCONFIG signal low.
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