Forum Discussion

Altera_Forum's avatar
Altera_Forum
Icon for Honored Contributor rankHonored Contributor
15 years ago

rx_freqlocked signal on Cyclone IV GX

I'm seeing strange behavior from the rx_freqlocked signal that's output from the Cyclone IV transceiver block in basic mode.

According to the transceiver documentation:

--- Quote Start ---

In automatic lock mode, the switch from LTR to LTD states is indicated by the

assertion of the rx_freqlocked signal and the switch from LTD to LTR states

indicated by the de-assertion of the rx_freqlocked signal.

--- Quote End ---

However, I'm seeing this signal asserted even when there's no data available at the receiver for the for the CDR to lock to.

Clearly I'm not understanding exactly what this signal is telling me. Does anyone have some insight on this?

Thanks

13 Replies

Show More
  • Altera_Forum's avatar
    Altera_Forum
    Icon for Honored Contributor rankHonored Contributor
    15 years ago

    After a month the results of my service request have been unfruitful. the rx_freqlocked signal seems to be simply broken in my system.

    I'm using Quartus 11.0sp1 on a Cyclone IV GX device. The altgxb is in basic mode.

    Does this signal work for anyone? What I'm seeing is the signal goes active after the receive analog reset is deasserted. It remains active no matter what happens on the data line. This is running in automatic lock mode.

    I've tried manual lock mode, but the signal behaves the same no matter what I do with the locktodata and locktoref lines. It indicates locked after releasing analog reset and remains stuck high no matter how I chance those inputs.

    If anyone has any insight into this it would be greatly appreciated!

    S
  • Altera_Forum's avatar
    Altera_Forum
    Icon for Honored Contributor rankHonored Contributor
    15 years ago

    Thanks for the suggestion.

    It seems to be constantly asserted, but I'll double check that.

    I found a knowledge base article that seems to describe the problem I'm seeing:

    http://http://www.altera.com/support/kdb/solutions/rd12152010_565.html (http://http//www.altera.com/support/kdb/solutions/rd12152010_565.html)

    This article indicates that the problem was caused by a bug in Quartus 10.1 and it links to a patch that fixes the problem. I'm using 11.0sp1, so hopefully that bug has been fixed. At any rate, there's no patch listed for 11.0sp1.

    I submitted a service request on this and will post here if I find anything out from that route.
  • Altera_Forum's avatar
    Altera_Forum
    Icon for Honored Contributor rankHonored Contributor
    15 years ago

    Are you seeing it toggle or remain asserted? In my experience this signal toggles (not necessarily every clock cycle) while the state machine attempts to lock to data. Depending on your device there's a Tltd_auto in the 4us range and the rx_freqlocked should be considered asserted only after it has remained high w/o transition for this amount of time.