On Wed, Jun 13, 2012 at 5:58 PM, Josh Blum <
address@hidden> wrote:
>
>
> On 06/13/2012 05:15 PM, Phelps Williams wrote:
>> I have a simple bpsk transmitter setup with a custom udp source block
>> which outputs a fixed pattern if no data is available from the socket.
>> I have instrumented the block to indicate when data is read from the
>> socket inside of work().
>>
>> My radio looks like this:
>> Custom UDP Source -> DPSK Mod (DBPSK, 10 samp/sym) -> Multiply Const
>> (0.3) -> UHD: USRP Sink
>>
>> My sample rate is 1e6.
>>
>> I can tell from my instrumented UDP Source that udp traffic is handled
>> by work and passed on almost immediately. However I can tell from
>> both monitoring the spectrum and the receiver output on the other side
>> that the data takes between 7 and 10 seconds before I see the expected
>> output from the N200. I thought this could be improved by reducing
>> the maximum socket buffer size (sudo sysctl -w
>> net.core.wmem_max=5000000) but that didn't seem to make a difference.
>> I went as low as wmem_max=10000 with no difference in delay. My goal
>> is to get the total delay to < 1sec.
>>
>> What else could be adding delay to my transmission path? Are there
>> other buffers I can tweak? Where else should I be looking?
>>
>
> Well the usrp only has a megabyte of buffering, as does the socket. At
> that rate, you couldnt not be buffering more than half a second's worth
> in the post-gnuradio part of the chain.
>
> I bet you have produced a lot of data all at once, filled up all of the
> gnuradio buffering, and you are simply measuring the time it takes to
> drain these buffers at a rate of 1Msps.
>
> If thats the case, you might pace your inputs. Or not transmit when you
> have nothing to transmit, this lets things flush out and idle.
>
> -josh
>
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