Re: Adding a Clock IP to RFNoC Block

Hey Jons,

I responded on the usrp-users list (didn't see that you had cross-posted).

--M

On Sat, Jul 26, 2025 at 10:18 AM Jons <jonsdeburn@gmail.com> wrote:

Hi all,

I am trying to add a custom RFNoC block and my block runs on different clocks(not the default ones). So I followed the instructions from the FAQ page in RFNoC wiki of deriving clocks from the available clocks - https://kb.ettus.com/RFNoC_Frequently_Asked_Questions#How_do_I_add_a_clock_with_a_different_frequency.3F But when I add the parameters in block YAML, it added new ports to my rfnoc_block_myblock module, which is not what I expected. My intention was to derive 2 clocks from the rfnoc_chdr_clk  and use it inside my block. For this I added the clock IP module (instantiated) in the noc_shell_myblock, because this is where the CDC FIFOs are there. So, with this method the generated clock just stays inside my block and won't be available outside to it. Maybe the steps described in the FAQ might not be the right way to go about with my requirement? I am not sure.

Also, I tried not adding the YAML parameters of the clocks for my block. This worked to the point where the implementation of the entire design failed with WNS of -0.8ns on the new derived clock I added. I also got a few Critical warnings for the clocks I added, not sure if it is related somehow or if I can ignore it -

TIMING-4#1 Critical Warning
Invalid primary clock redefinition on a clock tree  
Invalid clock redefinition on a clock tree. The primary clock x4xx_core_i/rfnoc_image_core_i/b_myblock_3/noc_shell_myblock_i/clk_wiz_chdr_200_125_inst/inst/clk_in_chdr is defined downstream of clock clk200 and overrides its insertion delay and/or waveform definition.

I followed this thread (https://www.mail-archive.com/usrp-users%40lists.ettus.com/msg14663.html) to add IPs of my clock module that I generated with with Vivado IP catalog and copied the .xci, .v and other generated files into the path/to/module/rfnoc/fpga/myblock/ip/ and changed the Makefile and block YAML definitions like the example given in the example Gain block.

Any tips or leads in adding custom derived clocks to the design would be super helpful and thank you all for maintaining such a nice community!!

-J