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DS90UB935-Q1: BIST mode question

Part Number: DS90UB935-Q1


Could you please help to provide more information to the following questions? Thank you.

Q1: If we enable BIST for about 30s, how many rounds of BIST would be executed? Is time consuming in every round the same? How long does it take to run single round BIST?

Q2: If the signal’s eye has problem during streaming, will it influence the FPS first (make FPS decrease), then lose lock. Or, it is going to lose lock directly. Like only two actions: streaming good or nothing?



  • Hello Roy,

    A1:  As mentioned in the 935 datasheet, "BIST mode is enabled by the BIST configuration register 0xB3[0] on the deserializer, and should only run in the synchronous mode. When BIST is activated at the deserializer, a BIST enable signal is sent to the serializer through the back channel. The serializer outputs a continuous stream of a pseudo-random sequence and drives the link at speed. The deserializer detects the test pattern and monitors the pattern for errors. The serializer also tracks errors indicated by the CRC fields in each back channel frame. While the lock indications are required to identify the beginning of proper data reception, the best indication of any link failures or data corruption is the content of the error counter in the BIST_ERR_COUNT register 0x57 for each RX port on the deserializer side." 

    The 935 just sends a pseudo-random bit sequence across the link and reports errors; it's at speed meaning the speed of the channel.
    So depending on their acceptable BER (bit error rate), is how long they should test for.
    A2:  If the signal’s eye has problem during streaming, the equalizer in the deserializer will try to recover the signal; however, if the link is not meeting our specification at all and the signal eye is closed or not meeting spec, then that will cause to lose the link lock. 
    Hope this helps.
    Shruti More
  • Hi Shruti,

    Thank you for your reply. Yes, we knew it is pseudo-random bit sequence. However, in datasheet, it doesn’t claim how long does every sequence take? I assume if we can know the time consuming of sequence, then the value of acceptable of BIST Error Count is clear to show in percentage?

    Like 10 BIST Error Count / 100 Total Sequence / maybe 20 seconds? Please help to let me know if I have any misunderstanding of pseudo-random bit sequence. Thank you.


  • Hello Roy,

    In the UB935, when BIST is activated, a continuous stream of a pseudo-random sequence is sent at 3-Gbps. You can enable BIST for however long you want, lets say for 30 seconds, then you would be sending 90Gb. You would then look at the BIST Error Count or the CRC error count to find out about any link failures or data corruption.

    So depending on their acceptable BER (bit error rate or ratio), is how long they should test for. The bit error rate (BER) is the number of bit errors per unit time. The bit error ratio (also BER) is the number of bit errors divided by the total number of transferred bits during a studied time interval. Bit error ratio is a unitless performance measure, often expressed as a percentage.

    I hope this helps.

    Best Regards,