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Re: [Discuss-gnuradio] UHD problem

From: Josh Blum
Subject: Re: [Discuss-gnuradio] UHD problem
Date: Thu, 15 Jul 2010 12:40:55 -0700
User-agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv: Gecko/20100527 Thunderbird/3.0.5

You have done nothing wrong. This is a result of the transmit SM in the FPGA using ethernet pause frames to flow control the transmit. The pause frame is blocking the transaction from the issue stream command, and causing the timeout error (no response).

Sending a large packet (greater than the fpga buffering) several seconds in the future will cause the FPGA to issue these pause frames and it will last for several seconds (until the transmit packets are processed).

Understanding that, it may be possible for you to work around this by making the sends in the future sooner (within 100 ms). Or issue the stream command before any sending occurs. In the long run, we are working on a host based flow control to avoid using the pause frames.

Hope that helps,

On 07/15/2010 12:16 PM, Per Zetterberg wrote:
Hi Josh and List,

I am trying to send two frames and then receive a frame. The two transmit frames are transmitted several seconds in 
advance using  d_dev->send. They arrive nicely at the receiver as they should. However, then I try to receive a frame  
using "d_sdev->issue_stream_cmd(stream_cmd)" followed by d_dev->recv. However, the command 
"d_sdev->issue_stream_cmd" gives the error "usrp2 no control response".

Could it be that when I do the command d_sdev->issue_stream_cmd the USPR2 is 
busy waiting to transmit the two transmit frames ?

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