[USRP-users] Transmission with timestamps

Josh Blum josh at ettus.com
Sat Jun 2 16:59:25 EDT 2012


> What is the best way to make the USRP reconsider the timestamps while
> the stream runs ? Is there a better way than dropping a packet, thereby
> creating an underrun ?
> 

Basically, set the end of burst on the last TX packet.
Then send the next packet with a new time.

The examples/tx_bursts.cpp should demonstrate this.

> I've also tried setting the end-of-burst, and with both
> STREAM_MODE_NUM_SAMPS_AND_MORE and STREAM_MODE_START_CONTINUOUS
> <http://files.ettus.com/uhd_docs/doxygen/html/structuhd_1_1stream__cmd__t.html#a4df1f2e22148b7e09ace0eca0dfbf904a91fa979980d1a6de6bf861b8459ed5c3>,
> but I get a lot of late packets (prints 'L' on the console). This
> approach seemed to be better, because the FSM would go back to IBS_IDLE,
> but I'm not sure I'm doing it right.
> 

Maybe there is some confusion, but the STREAM_MODE/stream command stuff
only applies to the RX side of things, its independent of TX.

> Furthermore, I have not quite understood what the stream mode
> influences. Is it changing the policy_next_packet and policy_next_burst
> in vita_tx_control.v ?
> 

This may help:
http://files.ettus.com/uhd_docs/doxygen/html/structuhd_1_1stream__args__t.html#a4463f2eec2cc7ee70f84baacbb26e1ef


-josh

> Best regards,
> 
> Matthias
> 
> [1]:
> by "packet" I mean the data given to the tx_streamer::send function.
> Please tell me if the official terminology differs.
> 

Too many layers and too many things are called packets :-)

I guess more specifically, its a "VRT IF data packet"

-josh




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