the uhd sink is not transmitting

Hello community,

i am transmitting simple continuous wave from uhd sink but the uhd sink after recognizing the device is not  transmitting any signal. i am attaching the log and snapshot of the program .please help me out.

the log:

Generating: '/home/wcc/grc_codes/top_block.py'

Executing: /usr/bin/python3 -u /home/wcc/grc_codes/top_block.py

[INFO] [UHD] linux; GNU C++ version 9.3.0; Boost_107100; UHD_4.0.0.0-46-g57ca4235

[INFO] [B200] Detected Device: B200mini

[INFO] [B200] Operating over USB 3.

[INFO] [B200] Initialize CODEC control...

[INFO] [B200] Initialize Radio control...

[INFO] [B200] Performing register loopback test...

[INFO] [B200] Register loopback test passed

[INFO] [B200] Setting master clock rate selection to 'automatic'.

[INFO] [B200] Asking for clock rate 16.000000 MHz...

[INFO] [B200] Actually got clock rate 16.000000 MHz.

[INFO] [B200] Asking for clock rate 40.000000 MHz...

[INFO] [B200] Actually got clock rate 40.000000 MHz.

[INFO] [MULTI_USRP] 1) catch time transition at pps edge

[INFO] [MULTI_USRP] 2) set times next pps (synchronously)

[INFO] [MULTI_USRP] 1) catch time transition at pps edge

[INFO] [MULTI_USRP] 2) set times next pps (synchronously)

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Regards