The JESD204C receiver is implemented with high speed flip-flops that are not single-upset-immune. As a result, the JESD204C link can experience various errors when exposed to radiation.
To improve the overall reliability of the link and make sure the link can automatically recover from an upset, several recommendations should be followed.
- Use subclass 1 operation by setting SUBCLASS=1.
- 64b/66b link encoding (JENC=1) is preferred over 8b/10b encoding. The 64b/66b link layer provides full-time block and EMB synchronization (pilot) signals, so misalignment caused by radiation can be detection quickly and consistently. In contrast, the 8b/10b link layer relies on synchronization characters that do not have a high occurrence rate, so misalignment takes longer to detect.
- Use a periodic and continuous SYSREF signal. Keep SYSREF alignment enabled at all times in the Tx and Rx devices. If radiation upsets the Tx or Rx LMFC/LEMC, the SYSREF signal will re-establish their phase and keep the Rx and Tx synchronized. If this recommendation is not followed, radiation can cause a persistent change in the link latency, or cause lanes to be persistently misaligned (causing persistent, corrupt samples to be sent to the DAC).
- 4. The transmitting logic device that provides data to the SerDes receiver should be designed with radiation tolerance in mind. Recommendations include:
- When possible, align counters continuously to SYSREF.
- FIFOs should have a means to detect and recover automatically from upsets that might cause overflow/underflow conditions.
- the user may program JTT to get an additional level of protection from functional interrupts.