Re: [Discuss-gnuradio] Last two data Blocks are always missing

[kaleem ahmad]

Dear Brian,

I have tried with different payload sizes and the maximum value I tried was
1024 bytes. But in all cases I never received last Block (Sorry in my first
post I mistakenly wrote last two blocks, it is actually the last block
only).

The length of transmit side filter is 125 and that of received side is 25.

Can you please explain how can I flush or clear the filters as you said:

"To alleviate, you may want to flush the filters out with all 0's for
at least the length of 1/2 the taps, but it might be better to clear
the whole thing just so if you decide to start a new burst, the filter
doesn't have anything left over to cause some weird transients at the
beginning of the burst."

Please give me a clue with little code if possible.

Thanks

Brian Padalino wrote:
> 
> On Tue, Aug 12, 2008 at 7:33 AM, kaleem ahmad <address@hidden>
> wrote:
>>
>> Hello Everyone,
>>
>> If you run following code on your machine (I am using gnradio3.1.1 and
>> this
>> code is also available in this version with a name 'fsk_loopback.py'
>> although it is removed in gnuradio3.1.2) then you will see that it will
>> transfer a file send.txt (Please create file named as "send.txt" in your
>> current folder) to another file "rcv.txt" (It will create that file by
>> itself).
>>
>> But the problem is it will never transfer the complete file but some data
>> at
>> the end is always missing and the amount of data missing depends on
>> "payload_size = ?" at line 38 in the following:
>>
>>        payload_size = 64             # bytes
>>
>> If the file is larger than 64 bytes let say 64 x 10 bytes then last two
>> blocks will be lost, and first 8 blocks will be received (You can run the
>> code given at the end without and USRP hardware, because it only tests
>> the
>> GNURadio and dont need any hardware).
>>
>> In short>
>>
>> 1-If the file is larger than the payload_size then last two blocks of
>> data
>> (2 x payload_size) are not received.
>>
>> 2-If the file is smaller than the payload_size then data is not
>> transferred
>> at all.
>>
>> For your convinience I have also attached send.txt and python code file
>> which you can directly download and run on your PC.
>>
>> Can some one give me some clue why this data is lost???????????
> 
> Just taking a stab in the dark here, but in your program there are a
> couple of low pass filters.  There is a finite group delay with those
> filters.  Do you know the length of your filters?
> 
> How large have you made your payload size?  I have a feeling that if
> you make your payload size relatively large, then you won't see the
> last few blocks missing, but instead a piece of the last block.
> 
> To alleviate, you may want to flush the filters out with all 0's for
> at least the length of 1/2 the taps, but it might be better to clear
> the whole thing just so if you decide to start a new burst, the filter
> doesn't have anything left over to cause some weird transients at the
> beginning of the burst.
> 
> Hope that helps.
> 
> Brian
> 
> 
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> Discuss-gnuradio mailing list
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> 
> 

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