Re: [Discuss-gnuradio] pipe trick

[Chuck Swiger]

At 03:02 AM 4/10/2005 -0400, you wrote:
> How are you _reading_ the data from the pipe?  Even if you're flushing
> the data into the pipe after every write, the reader could be
> buffering it.

Tks Dave - yes, yesterday I put a vector_sink_b after the 
file_descriptor_source
of the pipe and verified that it is reading ALL the date sent across it.
That is, after sending 20 \0xaa characters, the vector contains
(170, 170, 170, 170  ...  170, 170)   all 20 of them.

The little trickle of data going out to the usrp every byte written is 
interesting
and just now measured this:

bytes written to pipe   size of output to usrp  meaning
-----------------------------   ------------------------------- ------------
2                       49144                   6143 complex samples  49144 / 8
                                                6143+1 = 3 * 2048
                                                2048 is size of 
bytes_to_syms interpolation

3                       65528                   8191 complex samples
                                                8192+1 = 4 * 2048

4                       81912                   10239 complex samples
                                                10239+1 = 5 * 2048

etc


Every byte written to the pipe is /supposed/ to produce 8 * 2048 * 25 = 
409600 samples
the output rate to the usrp is 1.6msps (usrp interpolates by 80 to get 
128e6) so it only
has to write about 4 characters / second to the pipe to keep it stuffed ( 
or approximately
3.906 as Spock would say ).    Then, as soon as I close the pipe after 
getting these
little 'ticks'  of data, boom, it takes off and processes the data at full 
speed and produces
the correct output and prints text on a nearby receiver and psk31 software.

This didn't happen with a pipe head and a sound card sink - only with the 
usrp at the tail.
Even changed the bytes_to_syms interpolation back to 256 as in the sound 
card version,
but still get the same issue with the usrp.

Interestingly, the X25 interp fir filter doesn't show up mathematically in 
the output, even
tho it's in the stream. It's like the entire gnuradio stream is being 
clocked by the pipe and the
X2048 bytes_to_syms interpolator at the beginning.

--Chuck