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Visitor bitjockey
Visitor
1,816 Views
Registered: ‎03-21-2011

GTPA1_DUAL RX Clock Outputs - which is correct?

I noticed the GTP users guide makes mention (p. 93) of the RXRECCLKx recovered recieve clock outputs, but immediately recommends against their use in favor of their GTPCLKOUTx[1] copies. All of the illustrations show it this way too.

 

However the tranceiver code generated in the Ethernet 1000Base-X/SGMII LogiCore (as of v10.5, SGMII or dual enabled) uses the RXRECCLK0 output directly, and leaves GTPCLKOUT0[1] open.  What is the rationale behind this?

 

Is the core wrong?  Or is there an approprite/allowable use for the direct RXCLKOUTx ports? What gives?

 

Also, I found that the GTPCLKOUTx[1] port must go through a BUFIO2 in order to route to a BUFG, however RXRECCLK can get directly to a BUFG, as is done in the core, and seems easier to use.  Instantiated in hardware it seems to be working just fine.

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