[Discuss-gnuradio] Flowgraph running in "fits and starts"

[Marcus D. Leech]

I've got a flow-graph with a throttled random byte source, which is a
test input for a modulator:

http://www.sbrac.org/files/fm4_test_modulator.grc

http://www.sbrac.org/files/fm4_test_modulator.py

The source is throttled to the byte rate required to produce the correct
number of symbols/second (4800).

What I've noticed is that this graph only runs in "fits and starts",
rather than continuously.  I assume this has something to
  do with the Gnu Radio buffering and internal scheduler.

In the case of a "real" flow-graph, taking real data in at
4800symbols/second, going to a real USRP transmitter, will it still
  run in "fits and starts" or will it "do the right thing"??

I realize that buffering is an important part of Gnu Radio, but how do
you actually send low-rate data in something approaching
  correct real-time?

I at first thought this was due to the throttle block, so I replaced it
with an external (via a FIFO) source that produced random bytes
  at a 1200-bytes/second rate (2 bits/symbol), and it behaves exactly
the same as a a throttled random source--the graph seems to run in
  "fits and starts".


-- 
Marcus Leech
Principal Investigator
Shirleys Bay Radio Astronomy Consortium
http://www.sbrac.org