Thank you for the help. Is there somewhere where the command queue depth is 

Also is the same command queue used for both commands scheduled from 
rx_streamer and those scheduled with set_start_time()?

Thank you,


From: Sam Reiter <>
Sent: Wednesday, January 15, 2020 11:55 AM
To: Richard J. Muri
Subject: Re: [USRP-users] X310 scheduled issue_stream_cmd()


I believe what you're looking for is the depth of the command queue. For the 
X310, this FIFO has a depth of 16. Any command that you issue to the X310 that 
has a command time set will be held in this FIFO until the radio's time matches 
the command time, at which point the command is executed.

You should definitely keep track of the state of the command queue - 
overflowing this FIFO will put the radio in a bad state, usually requiring a 

Sam Reiter

On Tue, Jan 14, 2020 at 2:01 PM Richard Joseph Muri via USRP-users 
<<>> wrote:


I'm using an X310 with a number of scheduled receives. I suspect there is a 
FIFO on the USRP that holds the stream_cmd_t until it is time to collect the 
requested samples. I have not been able to find documentation about the size of 
this FIFO. Could anybody point me in the proper direction?

Do I need to keep track of the number of stream_cmds in the FIFO? Is there some 
kind of acknowledge I can use to know the stream_cmd has left the FIFO? At the 
moment I am running an C++ application with two threads, one to 
issue_stream_cmd(), and one to recv(). I loop each operation, posting a 
semaphore after each recv() and waiting on a semaphore before every 

I found this thread about using set_start_time():

Are these commands on the same FIFO issue_stream_cmd() uses?

Thank you!

Richard Muri

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