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Re: [Discuss-gnuradio] USRP2 start/stop issues

From: rwmcgwier
Subject: Re: [Discuss-gnuradio] USRP2 start/stop issues
Date: Sun, 6 Sep 2009 01:38:38 +0000

Nice job all!
Sent from my Verizon Wireless BlackBerry

-----Original Message-----
From: Tom Rondeau <address@hidden>

Date: Sat, 5 Sep 2009 17:26:13 
To: Eric Blossom<address@hidden>; Tom Rondeau<address@hidden>; GNURadio 
Discussion List<address@hidden>; Johnathan Corgan<address@hidden>
Subject: Re: [Discuss-gnuradio] USRP2 start/stop issues

On Fri, Sep 4, 2009 at 7:14 AM, Eric Blossom<address@hidden> wrote:
> On Tue, Sep 01, 2009 at 03:58:32PM -0700, Eric Blossom wrote:
>> On Tue, Sep 01, 2009 at 06:23:24PM -0400, Tom Rondeau wrote:
>> > I have an application where I have to start and stop the USRP2
>> > multiple times at various points, but I've been having trouble getting
>> > it to work. I traced it down to see that when the stop control message
>> > is sent, the host never processes the reply pack from the USRP2. Using
>> > Wireshark, I can see that this packet is being sent. After the failure
>> > of the stop command, the remaining commands to restart the USRP2 and
>> > set its parameters fail.
>> >
>> > To make this easier to debug, I found out that the simple program
>> > below exercises the problem nicely. To see the failures, I just print
>> > out the success message from "usrp2::impl::stop_rx_streaming" and from
>> > "usrp2::impl::start_rx_streaming" (in /usrp2/host/lib/usrp2_impl.cc).
>> > This is what happens:
>> >
>> > usrp2::stop_rx_streaming: success=1
>> > usrp2::start_rx_streaming: success=1
>> > usrp2::stop_rx_streaming: success=0
>> > usrp2::start_rx_streaming: success=0
>> > usrp2::stop_rx_streaming: success=0
>> >
>> > The first stop_rx_streaming comes during the initialization of the
>> > USRP2 to make sure its not streaming yet.
>> >
>> > Strangely (or maybe not; I can think of a some good reasons for this
>> > behavior), when you set the "rate" variable to above 300 to slow down
>> > the transmissions, everything works fine. At rate=200 it's flaky;
>> > sometimes it works and sometimes it doesn't. So there seems to be some
>> > timing issue involved.
>> >
>> > I've been looking and feel like I'm getting close to an answer, but it
>> > keeps escaping me. Any ideas on what's causing this?
> It's fixed!  I ran your test case 500 times w/o failure.
> There was a race in the code that notified the caller when the reply
> came in.  I also used your "don't enqueue when trying to stop" idea too.
> Please pull from http://gnuradio.org/git/eb.git u2-hang
> Eric

Hey. I thought I hit both you and Johnathan with a thank you email,
but looking back, looks like it only went to Corgan.

The fix works, so I'm well on my way with what I'm trying to do now.
Thank you very much for the quick turnaround on this.


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