Dear Ettus Support Team,
I hope this message finds you well. We are currently using the X310 (FPGA 39.2)
with a 10GigE interface, handling 1996 samples (4 bytes each) per packet.
Despite following all recommended setup tips and tricks for the USRP and our
Linux box, we occasionally encounter “U” (underflow) indicators. Below are
additional setup notes for your reference.
### Our Questions and Requests:
1. **FPGA Rx Buffer Size:**
* What is the FPGA Rx buffer size on the X310?
* I understand that this value cannot be set from the host side and requires
changes to the FPGA source. Could you confirm this understanding?
2. **Setting and Getting Host Parameters:**
* We are interested in setting and getting the values of three specific host
parameters: `num_send_frames`, `send_frame_size`, and `send_buff_size`.
* The Ettus documentation for "Transport Notes" mentions that values can be
specified using device arguments, which configure the transport, overriding the
default values chosen by UHD.
* How do we properly set and verify these values? The UHD API does not
provide a direct method to retrieve these parameters, making it unclear if they
are set correctly.
* For example, using `stream_args.args["foo"] = "512";` does not indicate an
error, so setting `num_send_frames` in the same way does not guarantee that the
value is applied. How can we ensure these settings are correctly applied?
3. **Suggestions for Mitigating Underflow ("U") Issues:**
* Could you provide suggestions on how to adjust our configuration or other
potential fixes to eliminate the "U" indicators?
### Setup Notes:
* **Operating System:** Ubuntu 20.04 Linux with Real Time scheduler at a very
high priority (-81).
* **Hardware Specifications:**
* 64 cores / 4 GPUs / >250GB RAM running at 3.5 GHz.
* Example analysis for CPU 63:
```
yamlCopy codedriver: intel_cpufreq
CPUs which run at the same hardware frequency: 63
CPUs which need to have their frequency coordinated by software: 63
maximum transition latency: 20.0 us.
hardware limits: 800 MHz - 3.50 GHz
available cpufreq governors: conservative, ondemand, userspace, powersave,
performance, schedutil
current policy: frequency should be within 800 MHz and 3.50 GHz.
The governor "performance" may decide which speed to use
within this range.
current CPU frequency is 3.50 GHz.
```
* **Software Settings:**
* Based on your recommendations, we
* See thread
https://lists.ettus.com/empathy/thread/P5LALBA6HSLEDTND4Z6IGTSZTEG3P5GX
* “For the first version can you try setting has_time_spec to false after the\
first packet is sent, and don't bother to set the time_spec on subsequent\
packets within a burst? The time_spec should really only be for the first\
packet. The radio will ignore the timestamp on the subsequent packets\
within a burst, and I noticed we set has_time_spec to false after the first\
packet in our benchmark_rate example.”
* https://kb.ettus.com/USRP_Host_Performance_Tuning_Tips_and_Tricks , not
using DPDK.
Thank you for your assistance and support. We look forward to your guidance on
these issues.
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