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Re: [Discuss-gnuradio] High packet loss problem (samples dropped?) and f

From: Dan Halperin
Subject: Re: [Discuss-gnuradio] High packet loss problem (samples dropped?) and fusb parameters
Date: Wed, 25 Jul 2007 12:53:54 -0700
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Hsin-mu Tsai wrote:
> 2. I guess I wasn't very clear in my first e-mail. I tried two
> different kinds of setting with file_sink and file_source:
> a)  TX_blocks -> usrp_source -> usrp board 1 ---physical_channel--->
> usrp board 2 -> usrp_sink -> file_sink
> then decode the signal with
> file_source -> RX_blocks
> b) TX_blocks -> file_sink
> then decode the signal with
> file_source -> RX blocks
> a) still has similar results while b) has 0 packet loss. a) doesn't
> involve real-time decoding (the CPU should have ample time to work
> with the data), but it still has a lot of packet losses.


> One of the weirdest thing is that even when I'm using only usrp_source
> -> file_sink, I can still have a lot of uO when using certain
> fusb_nblock and fusb_block_size setting (and I believe my machine is
> fast enough. I even tried saving the data to a file on the ramdisk).
> How does these settings affect the probability of USRP overrun? If I
> want to avoid samples being dropped, what setting should I use?

Yeah, it sounds like it's not CPU or disk overhead then -- how about
USB? I don't know much about the fast usb settings -- search the archive
for comments from wiser minds than I -- but you should definitely pick
settings that are free of 'uO's.

IIRC 802.15.4 is a 2 MHz (if you think of it as QPSK at twice the symbol
rate, that is) modulation scheme so this is going to be testing the
limits of USB if you sample at 2 4, or 8MHz complex (8, 16, 32 MBps
respectively). Have you benchmarked your USB speed (I think
gnuradio-examples/src/python/usrp/benchmark_usb is the accepted way to
do so these days)? Are there other USB devices attached to the computer?

>> Also, just to make sure, when you connect two USRPs directly make sure
>> to use sufficient attenuation (~40dB I think, check the archives for
>> emails from Matt Ettus for the actual number) with any of the RFX boards
>> to avoid damage to the receiver!
> That's good to know! (I didn't know this.) Is there anyway to make
> sure that my board is not damaged?

Not my area.

- -Dan
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