03-13-2018 05:49 AM - edited 03-13-2018 06:27 AM
What are the possible reasons that can cause RXUSRCLK2, RXUSRCLK, and RXOUTCLK turned OFF abnormally in 7 Series GTX? It seems that RXOUTCLK from GTX is turned off without any apparent reason and hence RXUSRCLK2, RXUSRCLK are also turned off.
Followings are the status of relevant signals,
RXUSERRDY = 1'b1,
[RX/TX]PD = 2'b10,
[TX/RX]RESETDONE = 1'b1,
TXELECIDLE = 1'b1,
TXDETECTRX = 1'b0,
RXOUTCLKSEL = 3'b010,
RXSYSCLKSEL = 2'b11
QPLLRESET = 1'b0,
All Reset related signals are low.
RXOUTCLK gets turned off as soon as [RX/TX]PD is change from 2'b00 to 2'b10 with TXELECIDLE = 1'b1.
What can cause this issue? Does this have anything to do with signalling on GTX[RXP/RXN]?
03-13-2018 07:57 AM
The PD in RXPD stands for power down. It will turn off the clocks. It is an input to the GT so it is something you should have control over. Perhaps you're using some ip (PCIE) that is doing this. If so it would be a better question for the networking experts.
03-13-2018 08:00 AM
USRCLK are commonly driven by OUTCLK, so if the OUTCLK goes flat, also the USRCLK will be flat.
RX/TXPD is the GT powerdown. If you toggle it from normal operation (00) to longer recovery time (10) something will happen.
Please notice that PD might trigger a reset, and just after reset the OUTCLK could have holes for short time.
Additionally, after RXPD is deasserted, GTRXRESET must be toggled.
hope it helps
03-13-2018 09:16 AM
03-13-2018 09:54 AM
RXELECIDLE is an output port. When it goes HIGH this means that the input signal level is below a threshold.
If this happens, probably the signal is not available at receiver pins, thus the CDR cannot make its job of recovering clock and data, and probably the reset FSM detects errors and starts resetting the receiver periodically.
03-13-2018 09:57 AM - edited 03-13-2018 10:02 AM
@gguasti I am not seeing any RESET coming to _gt module when clock becomes off. For which reset FSM are you talking about?
If rx line is ELECIDLE then it will not have phase frequency adaption but rxoutclk must be there, I believe.