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DS90UB948-Q1: link and lock state are inconsistent

Zirui Su
Expert 5340 points
Part Number: DS90UB948-Q1

Hi team

When we use 941-948,at 941 side we may use link detect status to check whether the 948-941 back channel link status is OK and use lock pin from 948 to check whether the 941-948 forward channel will be OK. The question is:

Some time when we see the 941 0x0C bit[0] link status lost, the 948 lock pin still be high, so what could lead to this phenomenon and how could we improve the screen side since my customer conducted the 948 side rather than the SoC-941 side, thank you.

  • 0
    TI__Guru 66840 points

    Hi Zirui, 

    These two fields are different mechanisms and observe different conditions, so it is possible for one to go low, while the other remains high.

    To elaborate, see below summary: 

    Device Register Field Condition
    941 Link Detect

    Link Detect status for selected port: 1: Cable link detected 0: Cable link not detected

    Based on LINK_DETECT_TIMER (0x26) time-out period.

    Bidirectional Control Channel Link Detect Timer This field configures the link detection timeout period. If the timer expires without valid communication over the reverse channel, link detect will be deasserted
    941 Link Lost Link Lost Flag for selected port: This bit indicates that loss of link has been detected. This register bit will stay high until cleared using the CRC ERROR RESET in register 0x04
    948 Lock

    Indicates if De-Serializer is locked to input data

    1: De-Serializer locked to recovered clock

    0: De-Serializer not locked

    The 948 lock status depends on clock recovery from 941, whereas the 941 link detect depends on receiving valid back-channel frames from the 948. 

    Regards, 

    Logan

  • 0 in reply to Logan Cummins
    TI__Expert 5340 points

    Hi Logan

    Yes I have known that it is possible one goes low and the other goes high. Could you please provide some suggestions at 948 side since my customer is conducting the screen side project, and what should we do to re-high the 941 link detect status if we see the link detect is low at 941 side while 948 side is lock, any possible reasons or causes due to the issue? Thank you.

  • 0 in reply to Zirui Su
    TI__Guru 66840 points

    Hi Zirui, 

    You can increase the LINK_DETECT_TIMER (0x26) time-out period to potentially keep the LINK_DETECT from going low. 

    Zirui Su said:
    what should we do to re-high the 941 link detect status if we see the link detect is low

    In cases where LINK_DETECT goes low, does it remain low until reset? It would be surprising that you would completely lose the back channel while still having the link lock (LINK_LOST in 941, and LOCK in 948).

    Regards, 

    Logan