02-28-2019 10:06 PM
In 7 series GTX transceiver, for CTLE equalization the boost settings can be varied by using RX_DFE_KL_CFG2 [31:0] register. But to change the DFE tap values there is no information given in UG476_7series_Transceiver_Guide. Can someone guide me how to set the appropriate DFE tap values?
02-28-2019 11:29 PM
typically, tuning DFE taps are not recommanded.
what is the issue that you encounter? please share some lights about why you wanted to tune DFE taps.
03-01-2019 12:44 AM
Because for line-rate more than 10gbps,the link won't be stable. The link will be fluctuating, if I set the CTLE in auto-adapting mode or if I change CTLE in fixed mode . So I cannot get the eye-diagram properly. Hence I am planning to change the DFE tap values, so that the link will be stable.
03-01-2019 12:56 AM
I'm afraid tuning DFE Taps manually may not help.
what's the transmitter?
can IBERT be used for testing?
03-01-2019 03:05 AM
As Boris suggested, in the lucky case you will find a combination of parameters that will give you "a more stable result", this will be valid for the particular board in the particular temperature and power, on your particular laboratory desk :-) and cannot be a solution for the final product.
This is the reson why we are a bit reluctant to hack the DFE.
I would rather try to investigate more on the reason of the unstability:
03-01-2019 04:56 AM
You had specified that we can monitor weather TAPs are saturating using DMONITOROUT[7:0]. Let's take we are monitoring DFETAP2 . and DMONITOR_CFG value equal to default value. In ug476 it is given that
" RXDFETAP2 [5:0] = DMONITOROUT[5:0]
6'd0 = 0
6'd63 = Full scale "
I am not understanding how this will tell weather DFETAP2 working or not. Can you please help me with this.
and I had already taken care of other points what you mentioned.
03-04-2019 01:48 AM
TAPx = 0 can be possible, but generally a saturated (Full scale) tap is not a wanted condition.
If this happens, you might try to tune the far end TX pre-post de-emphasis and CTLE setup.