rfnoc_radio_loopback with rx-timestamps set to true always results in an overflow #956

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1. mbr0wn commented on Nov 13, 2026

   

   mbr0wn

   on Nov 13, 2026

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   This is expected behaviour -- in fact, this use case is why we have that API in the first place. I agree though it's weird to not document that in the example.

   👍React with 👍1Reacted by climb4life
2. climb4 commented on Nov 13, 2026

   

   climb4

   on Nov 13, 2026

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   Thank you very much for clarifying.

   As a bit of a follow up, with the RX timestamps disabled I can now successfully run the loopback example (and my own derived code).
   However, as soon as I add blocks in the chain (using my own custom image) to the two radio blocks the overflow issues come back.

   I have now tried pretty much everything that came to mind, my goal is to create a chain of radio -> ddc -> custom OOT block -> duc -> radio, but even with just radio -> ddc -> duc -> radio, an overflow shows up.
   No matter the image's CHDR width, the buffer sizes of the stream endpoints and whether I connect them statically or dynamically.
   Is there something I'm missing? In my current version the CHDR width is 256 and each endpoint has a buffer size of 65536. I then connect everything up dynamically with each block having 2 dedicated stream endpoints (since NUM_PORTS is set to 2 for each of the 3).
3. climb4 commented on Nov 13, 2026

   

   climb4

   on Nov 13, 2026

   Last edited by climb4

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   For reference, this is the image_core.yml I'm using:

   schema: rfnoc_imagebuilder_args
   copyright: TODO
   license: TODO
   version: '0.1'
   chdr_width: 256
   image_core_name: 'x4xx_image'
   default_target: 'X410'
   inherit:
   - 'yaml_include/x4xx_x4_base.yml'
   device: 'X410'
   
   parameters:
       RF_BW: 400
       ENABLE_DRAM: False
       NUM_DRAM_BANKS: 0
       NUM_DRAM_CHANS: 0
       DRAM_WIDTH: 64
   
   stream_endpoints:
       ep0:
           ctrl: True
           data: True
           buff_size_bytes: 65536
       ep1:
           ctrl: False
           data: True
           buff_size_bytes: 65536
       ep4:
           ctrl: False
           data: True
           buff_size_bytes: 65536
       ep5:
           ctrl: False
           data: True
           buff_size_bytes: 65536
       ep6:
           ctrl: False
           data: True
           buff_size_bytes: 65536
       ep7:
           ctrl: False
           data: True
           buff_size_bytes: 65536
   
   noc_blocks:
       radio0:
           block_desc: 'radio.yml'
           parameters:
               NUM_PORTS: 2
           ctrl_clock: _device_.rfnoc_ctrl
           timebase_clock: _device_.radio
       duc0:
           block_desc: 'duc.yml'
           parameters:
               NUM_PORTS: 2
       ddc0:
           block_desc: 'ddc.yml'
           parameters:
               NUM_PORTS: 2
   
   connections:
       - { srcblk: radio0,     srcport: ctrlport,  dstblk: _device_,   dstport: ctrlport_radio0    }
       - { srcblk: _device_,   srcport: radio0,    dstblk: radio0,     dstport: radio              }
       - { srcblk: _device_,   srcport: time,      dstblk: radio0,     dstport: time               }
   
       - { srcblk: ep0,    srcport: out0,  dstblk: radio0, dstport: in_0   }
       - { srcblk: radio0, srcport: out_0, dstblk: ep0,    dstport: in0    }
   
       - { srcblk: ep1,    srcport: out0,  dstblk: radio0, dstport: in_1   }
       - { srcblk: radio0, srcport: out_1, dstblk: ep1,    dstport: in0    }
   
       - { srcblk: ep4,    srcport: out0,  dstblk: duc0,   dstport: in_0   }
       - { srcblk: duc0,   srcport: out_0, dstblk: ep4,    dstport: in0    }
   
       - { srcblk: ep5,    srcport: out0,  dstblk: duc0,   dstport: in_1   }
       - { srcblk: duc0,   srcport: out_1, dstblk: ep5,    dstport: in0    }
   
       - { srcblk: ep1,    srcport: out0,  dstblk: radio0, dstport: in_1   }
       - { srcblk: radio0, srcport: out_1, dstblk: ep1,    dstport: in0    }
   
       - { srcblk: ep6,    srcport: out0,  dstblk: ddc0,   dstport: in_0   }
       - { srcblk: ddc0,   srcport: out_0, dstblk: ep6,    dstport: in0    }
   
       - { srcblk: ep7,    srcport: out0,  dstblk: ddc0,   dstport: in_1   }
       - { srcblk: ddc0,   srcport: out_1, dstblk: ep7,    dstport: in0    }
   
   clk_domains:
       - { srcblk: _device_,   srcport: radio, dstblk: radio0, dstport: radio  }
       - { srcblk: _device_,   srcport: ce,    dstblk: duc0,   dstport: ce     }
       - { srcblk: _device_,   srcport: ce,    dstblk: ddc0,   dstport: ce     }

   And the graphviz dot file for the connected graph:

   digraph rfnoc_graph {
     rankdir=LR
     node [shape=record]
   
     subgraph "cluster_0/Radio#0" {
       label="0/Radio#0"
       "0/Radio#0_in" [label="in|<in_0> 0|<in_1> 1"]
       "0/Radio#0_out" [label="out|<out_0> 0|<out_1> 1"]
     }
     "0/Radio#0_in" -> "0/Radio#0_out" [style=invis]
   
     subgraph "cluster_0/DDC#0" {
       label="0/DDC#0"
       "0/DDC#0_in" [label="in|<in_0> 0|<in_1> 1"]
       "0/DDC#0_out" [label="out|<out_0> 0|<out_1> 1"]
     }
     "0/DDC#0_in" -> "0/DDC#0_out" [style=invis]
   
     subgraph "cluster_0/DUC#0" {
       label="0/DUC#0"
       "0/DUC#0_in" [label="in|<in_0> 0|<in_1> 1"]
       "0/DUC#0_out" [label="out|<out_0> 0|<out_1> 1"]
     }
     "0/DUC#0_in" -> "0/DUC#0_out" [style=invis]
   
   
     "0/Radio#0_out":"out_0" -> "0/DDC#0_in":"in_0" [label="dynamic"]
     "0/DDC#0_out":"out_0" -> "0/DUC#0_in":"in_1" [label="dynamic"]
     "0/DUC#0_out":"out_1" -> "0/Radio#0_in":"in_1" [label="dynamic"]
   }

   Could this be a limitation of the single-sample implementation of DDC and DUC of UHD 4.9.0.0 so I'd have to either update to 4.11.0.0 or lower the bandwidth?
4. climb4

   closed this as completedon Nov 13, 2026