Re: [Discuss-gnuradio] attribute/control stream question

[Matt Ettus]

Eric A. Cottrell wrote:
> Hello,
>
> The processing of pulses into data requires me to keep track of valid
> pulses (following samples are above threshold) and leading edges (sample
> is 6 dB or more than previous sample and following sample is 6 dB or
> less than current sample).  I also want to indicate preamble start and
> pass timestamps along.  I have thought of three methods to do this but
> do not know which would be the best one.
>
>   

You can do this, or you may be able to break things up into chunks of
samples and process them as vectors.  See the ofdm_sync code for an
example of how we do that.

> The first method is to have two streams through the blocks, one a float
> stream containing the sample values and the other a short or int stream
> containing the attributes and control.  The float data makes it easier
> to do processing as some of the blocks use 3 dB multiplication of the
> samples (1.414 and 0.707).  Being an old programmer I still have the
> float equals slow performance mindset.
>
> The second method is to have the two streams as shorts.  I have to deal
> with an integer multiplication and division (sample * 707 / 1000).  I
> have no handle if integers would be faster than floats other than
> integer division tends to be expensive.
>   

Float multiplication is 1 cycle.  Integer multiplication can actually be
slower these days.

> The third method is to use one integer stream and have the upper 16 bits
> be the attributes/control and the lower 16 bits be the value.  This
> method has an additional minor disadvantage over the second method of
> needing to mask off the upper 16 bits when using the value but I do not
> have to deal with two streams.
>   

I would use separate streams so you don't need to play with bit fields. 
There are a number of places in the OFDM code where we use chars in
parallel with vectors of floats, and it works well for us.


Matt