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Is there a signal from the ALTGX indicating the CDR is locked to the incoming data?

Altera_Forum
Honored Contributor II
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I need to know when the ALTGX's CDR is locked to the incoming data rate, but there doesn't seem to be a signal that serves this purpose. The rx-freqlocked is almost this signal, but not quite.  

 

My design uses the CDR in auto mode. The rx-freqlocked signal is asserted when the CDR is locked to the incoming data, but it is also asserted when the ALTGX is locked to the reference clock. 

 

The functionality of this signals isn't completely clear in the transceiver architecture spec, but this is the functionality I have observed in my live system. I notice that the rxfreq-locked signal is asserted when the incoming data rate doesn't match the data rate the ALTGX is configured to receive. When I initiate a reconfiguration of the data rate, the rx-freqlocked signal is cleared for a short while, then is asserted again - regardless of the incoming data rate. 

 

I am using the CDR in auto mode because in the architecture spec it says the rxfreq-locked signal is always high if the CDR was in LTD mode which isn't helpful - unless it is high when the CDR is actually locked to the incoming data. 

 

Is there an output from the ALTGX which indicates when the CDR is locked to the incoming data?
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Altera_Forum
Honored Contributor II
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Did you ever find a solution to this problem?

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Altera_Forum
Honored Contributor II
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The answer is that there is no signal that indicates the receiver is locked to the incoming data stream. The signal "rxfreq_locked" indicates that the CDR is currently in lock-to-data mode. This is why manually asserting ltd will force this signal high. The only way to somewhat determine if the receiver is locked is to monitor the "rxfreq_locked" signal. If it remains asserted for a period of time (meaning the receiver remains in lock-to-data mode) then you can assume it is locked. If the signal deassert, you are not locked to the incoming data stream.

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