On 17/06/2024 21:16, cjohn...@serranosystems.com wrote:
I hacked the code to set the DATA_FRAME_MAX_SIZE = 8500, half-way
between 8000 and MTU 9000.
Then I made sure to set the send_frame_size=recv_frame_size=8700,
which is equal, and over the MAX_SIZE.It still picks 8144. You can see
below.
I added a bunch of debug of the intermediate variables.
$~/uhd-4.6.0.0/host/build/examples$ ./tx_samples_c -a
"type=x300,addr=192.168.40.2,send_frame_size=8700,recv_frame_size=8700"
|Creating USRP with args
"type=x300,addr=192.168.40.2,send_frame_size=8700,recv_frame_size=8700"...|
|[INFO] [UHD] linux; GNU C++ version 9.4.0; Boost_107100;
UHD_4.6.0.0-1-ga9f0b4c7|
|[INFO] [X300] X300 initialization sequence...|
|[INFO] [X300] user_frame_size.send_frame_size: 8700|
|[INFO] [X300] x300::DATA_FRAME_MAX_SIZE: 8500|
|[INFO] [X300] std::min(user_frame_size.send_frame_size,
x300::DATA_FRAME_MAX_SIZE): 8500|
|[INFO] [X300] max_send_frame_size: 8500|
|[INFO] [X300] min_recv_frame_size: 8144|
|[INFO] [X300] min_send_frame_size: 8144|
|[INFO] [X300] Maximum frame size: 8144 bytes.|
|[WARNING] [X300] You requested a receive frame size of (8700) but
your NIC's max frame size is (8144).Please verify your NIC's MTU
setting using 'ip link' or set the recv_frame_size argument
appropriately.UHD will use the auto-detected max frame size for this
connection.|
|[WARNING] [X300] You requested a send frame size of (8700) but your
NIC's max frame size is (8144).Please verify your NIC's MTU setting
using 'ip link' or set the send_frame_size argument appropriately.UHD
will use the auto-detected max frame size for this connection.|
|[WARNING] [X300] For the 192.168.40.2 connection, UHD recommends a
send frame size of at least 8500 for best|
|performance, but your configuration will only allow 8144.This may
negatively impact your maximum achievable sample rate.|
|Check the MTU on the interface and/or the send_frame_size argument.|
|[WARNING] [X300] For the 192.168.40.2 connection, UHD recommends a
receive frame size of at least 8500 for best|
|performance, but your configuration will only allow 8144.This may
negatively impact your maximum achievable sample rate.|
|Check the MTU on the interface and/or the recv_frame_size argument.|
|[INFO] [GPS] Found an internal GPSDO: LC_XO, Firmware Rev 0.929a|
|[INFO] [X300] Radio 1x clock: 200 MHz|
|Setting TX Rate: 200000000.000000...|
|Actual TX Rate: 200000000.000000...|
|Setting TX Gain: 0.000000 db...|
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Well, as Wade pointed out, the MTU limit in the FPGA is 8192. I don't
know whether the UHD 'stack' is using PMTUD, or
some other technique. With PMTUD (Path MTU Discovery), even if your
NIC MTU is 9000, with PMTUD, things will
be configured for the largest MTU that the path can actually
support. In this case, with the FPGA supporting a max
of 8192, the numbers quoted make sense...
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