[Discuss-gnuradio] forecast in infinite loop

[Jared Dulmage]

Ubuntu 14.04, GR 3.7.8

I apologize if this question is a duplicate, I never received a confirmation of 
my original request in the mailing list digest.  I appreciate any insights or 
advice to diagnose the issue presented below.

>From a high level, I am trying to create a block that acts like a gate, i.e. 
>in the locked state, the block passes all inputs to the output;  in the 
>unlocked state the block consumes its input and provides no output.  The state 
>depends on a count of consecutive events (misses) where the block's state 
>changes to locked (unlocked) when a threshold is met.  Events are marked by 
>stream tags on the input at a regular interval.  So there is no a priori known 
>relationship between input and output.  I've seen this thread which I believe 
>is related:

https://lists.gnu.org/archive/html/discuss-gnuradio/2013-01/msg00039.html

but I can't seem to determine a solution from that discussion.  My block is 
called frame_sync_c and is a python block.

My test flowgraph looks like

vector_source_c -> throttle -> frame_sync_c -> null_sink

The vector source has tags placed periodically with a gap in the tag sequence.  
The block behaves completely as expected for a number of lock/unlock cycles and 
then devolves into an infinite loop of forecast calls without calling 
general_work.  Below is a sample log that shows the forecast calls, 
noutput_items and nitems_read(0) in each general_work call and consume calls.  

Consume calls are prefixed by the current block state, Locked or Unlocked.  
"Consume & produce X" means the block called self.consume(0,X) and also 
returned X.  "Consume X" means self.consume(0,X) was called and 0 was returned 
(i.e. no output was produced).  The block generally consumes up to a state 
transition and then relies on another call to general_work to continue 
processing with the new state.  Interestingly, the block seems to devolve after 
around 3000 samples regardless of the vector_source_c data size, tag period, or 
other parameters related to the input stream.

gr::debug :INFO: frame_sync_c0 - Forecast 4096
gr::debug :INFO: frame_sync_c0 - Forecast 2048
gr::debug :INFO: frame_sync_c0 - Forecast 1024
gr::debug :INFO: frame_sync_c0 - Forecast 512
gr::debug :INFO: frame_sync_c0 - Forecast 256
gr::debug :INFO: frame_sync_c0 - Forecast 128
gr::debug :INFO: frame_sync_c0 - Forecast 64
gr::debug :INFO: frame_sync_c0 - Forecast 32
gr::debug :INFO: frame_sync_c0 - Forecast 16
gr::debug :INFO: frame_sync_c0 - Forecast 8
gr::debug :INFO: frame_sync_c0 - Forecast 4
gr::debug :INFO: frame_sync_c0 - Forecast 2
gr::debug :INFO: frame_sync_c0 - Forecast 1
gr::debug :INFO: frame_sync_c0 - Forecast 4096
gr::debug :DEBUG: frame_sync_c0 - noutput_items = 4096, nitems_read(0) = 0, 
key_tags @ 10, 110, 210, 310, 410, 510, 610, 710
gr::debug :DEBUG: frame_sync_c0 - Unlocked: Consume 410
gr::debug :INFO: frame_sync_c0 - Forecast 4096
gr::debug :INFO: frame_sync_c0 - Forecast 2048
gr::debug :DEBUG: frame_sync_c0 - noutput_items = 2048, nitems_read(0) = 410, 
key_tags @ 410, 510, 610, 710
gr::debug :DEBUG: frame_sync_c0 - Locked: Consume & produce 600
gr::debug :INFO: frame_sync_c0 - Forecast 4096
gr::debug :INFO: frame_sync_c0 - Forecast 2048
gr::debug :DEBUG: frame_sync_c0 - noutput_items = 2048, nitems_read(0) = 1010, 
key_tags @ 
gr::debug :DEBUG: frame_sync_c0 - Unlocked: Consume 2048
gr::debug :INFO: frame_sync_c0 - Forecast 4096
gr::debug :INFO: frame_sync_c0 - Forecast 2048
gr::debug :INFO: frame_sync_c0 - Forecast 1024
gr::debug :DEBUG: frame_sync_c0 - noutput_items = 1024, nitems_read(0) = 3058, 
key_tags @ 
gr::debug :DEBUG: frame_sync_c0 - Unlocked: Consume 1024
gr::debug :INFO: frame_sync_c0 - Forecast 4096
gr::debug :INFO: frame_sync_c0 - Forecast 2048
gr::debug :INFO: frame_sync_c0 - Forecast 1024
gr::debug :INFO: frame_sync_c0 - Forecast 512
gr::debug :INFO: frame_sync_c0 - Forecast 256
gr::debug :INFO: frame_sync_c0 - Forecast 128
gr::debug :INFO: frame_sync_c0 - Forecast 64
gr::debug :INFO: frame_sync_c0 - Forecast 32
gr::debug :INFO: frame_sync_c0 - Forecast 16
gr::debug :INFO: frame_sync_c0 - Forecast 8
gr::debug :DEBUG: frame_sync_c0 - noutput_items = 8, nitems_read(0) = 4082, 
key_tags @ 
gr::debug :DEBUG: frame_sync_c0 - Unlocked: Consume 8
gr::debug :INFO: frame_sync_c0 - Forecast 4096
gr::debug :INFO: frame_sync_c0 - Forecast 2048
gr::debug :INFO: frame_sync_c0 - Forecast 1024
gr::debug :INFO: frame_sync_c0 - Forecast 512
gr::debug :INFO: frame_sync_c0 - Forecast 256
gr::debug :INFO: frame_sync_c0 - Forecast 128
gr::debug :INFO: frame_sync_c0 - Forecast 64
gr::debug :INFO: frame_sync_c0 - Forecast 32
gr::debug :INFO: frame_sync_c0 - Forecast 16
gr::debug :INFO: frame_sync_c0 - Forecast 8
gr::debug :INFO: frame_sync_c0 - Forecast 4
gr::debug :DEBUG: frame_sync_c0 - noutput_items = 4, nitems_read(0) = 4090, 
key_tags @ 
gr::debug :DEBUG: frame_sync_c0 - Unlocked: Consume 4
gr::debug :INFO: frame_sync_c0 - Forecast 4096
gr::debug :INFO: frame_sync_c0 - Forecast 2048
gr::debug :INFO: frame_sync_c0 - Forecast 1024
gr::debug :INFO: frame_sync_c0 - Forecast 512
gr::debug :INFO: frame_sync_c0 - Forecast 256
gr::debug :INFO: frame_sync_c0 - Forecast 128
gr::debug :INFO: frame_sync_c0 - Forecast 64
gr::debug :INFO: frame_sync_c0 - Forecast 32
gr::debug :INFO: frame_sync_c0 - Forecast 16
gr::debug :INFO: frame_sync_c0 - Forecast 8
gr::debug :INFO: frame_sync_c0 - Forecast 4
gr::debug :INFO: frame_sync_c0 - Forecast 2
gr::debug :DEBUG: frame_sync_c0 - noutput_items = 2, nitems_read(0) = 4094, 
key_tags @ 
gr::debug :DEBUG: frame_sync_c0 - Unlocked: Consume 2
gr::debug :INFO: frame_sync_c0 - Forecast 4096
gr::debug :INFO: frame_sync_c0 - Forecast 2048
gr::debug :INFO: frame_sync_c0 - Forecast 1024
gr::debug :INFO: frame_sync_c0 - Forecast 512
gr::debug :INFO: frame_sync_c0 - Forecast 256
gr::debug :INFO: frame_sync_c0 - Forecast 128
gr::debug :INFO: frame_sync_c0 - Forecast 64
gr::debug :INFO: frame_sync_c0 - Forecast 32
gr::debug :INFO: frame_sync_c0 - Forecast 16
gr::debug :INFO: frame_sync_c0 - Forecast 8
gr::debug :INFO: frame_sync_c0 - Forecast 4
gr::debug :INFO: frame_sync_c0 - Forecast 2
gr::debug :INFO: frame_sync_c0 - Forecast 1
---- repeats Forecast 4096 to Forecast 1 lines forever ----

Jared.
------------------------------------------------------
Jared Dulmage
Engineering Specialist
Digital Comm. and Implementation Dept.
Aerospace Corporation
310-336-3140