Re: [Discuss-gnuradio] gr_delay behavior

[Carlos Aviles]

Hi Martin,

Thanks for the answer and my apologies for the guessing work.

I reviewed my test code and it turns out that, as you say and as I was
expecting, gr_delay works fine. A custom block I built is the one to
blame for the misbehavior I'm seeing.
I'll work on my custom block and eventually post another question in
case I can't figure out by myself the problem.

Thanks,
Carlos.


On Mon, Feb 22, 2010 at 1:51 PM, Martin Braun <address@hidden> wrote:
> On Mon, Feb 22, 2010 at 10:42:08AM +0100, Carlos Aviles wrote:
>> gr_delay is intended to delay the input of the signal by n samples.
>> I've been doing some testing with that block and I have observed that
>> the delay is applied to the chunk of data that the block receives as
>> input (on my case that was some 8000 samples) and applied again to the
>> next chunk.
>>
>> I see two problems with that.
>>
>> - I'm not able to apply the delay once (to the very beginning of the
>> signal). This is actually a very trivial problem that could be solved
>> building a custom block.
>> - If the delay I want to apply is larger than the size of the data
>> that the block receives (say a delay of 10000 samples when the block
>> receives the data in chunks of 8000 samples), the signal is set to 0
>> as if applying an infinite delay.
>
> If you'd have pasted some code, the diagnosis would have been a bit
> simpler, but I'll give it a try:
>
> gr_delay works as you explained. If you set delay to N, the first N-1
> outputs will be zero, after that, everything will work as expected.
> Of course, you must send at least N items before you get anything at
> the output.
>
> Concerning your second point: what do you mean by chunk size? Are you
> talking about what GNU Radio passes between blocks? If so, ignore that,
> GNU Radio will do the right thing. Or have you set itemsize to 8000 *
> gr.sizeof_gr_float? In that case, remember you have to pass 800000000
> samples (in blocks of 8000 samples each) through gr_delay before you've
> reached a delay of 10000.
>
> Please post your questions such that the answer requires less guesswork.
>
> MB
>
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