Re: [Discuss-gnuradio] Slow down rate of Python source block

[Tom Rondeau]

On Thu, Jul 31, 2014 at 12:21 PM, David Halls <address@hidden> wrote:

Dear All,

I have a Python block that produces packets of size 1536 bytes. Due to various reasons, the latter parts of my flow graph are very slow (this is desired and cannot be changed). After producing 510 packets, I get the following error.

"handler caught exception: operands could not be broadcast together with shapes (1527) (1536)
Traceback (most recent call last):
File "/usr/local/lib/python2.7/dist-packages/gnuradio/gr/gateway.py", line 55, in eval
try: self._callback()
File "/usr/local/lib/python2.7/dist-packages/gnuradio/gr/gateway.py", line 160, in __gr_block_handle
) for i in self.__out_indexes],
File "/usr/local/lib/python2.7/dist-packages/trl/blsd_enc_b.py", line 198, in work
out_cA[0:len(cAm)] = cAm
ValueError: operands could not be broadcast together with shapes (1527) (1536)
thread[thread-per-block[1]: <block blsd_enc_b (2)>]: caught unrecognized exception"

Debugging more carefully, I can see that:

len(cAm) = 1536 , len(out_cA) = 32768

Just a quick response without really studying the problem or your code. The dynamic scheduler in GR is getting in your way, and the throttle block is definitely not the right way to help you. You need to either tell the scheduler what you need it to send your block or handle it internally. There are three ways to solve these issues:

1. Use set_output_multiple in the constructor, which will only allow the scheduler to send you chunks of data of some multiple of the number you pass that. I've seen this slow down the scheduler in other situations, but it sounds like you're going slow, anyways, so this shouldn't cause a problem.

2. Make your input signature your packet_length so each item will be a vector of that length. This would not be my preferred way, but we've played that game before.

3. Handle it internally. Buffer up the input until you have enough to produce what you need. You'd need to inherit from gr.basic_block here and do more management of the data and buffers yourself.

Tom

 

for the first 490 packets, and then the length of 'out_cA' begins to reduce

packet_num = 490
len(cAm) = 1536 , len(out_cA) = 32247
packet_num = 491
len(cAm) = 1536 , len(out_cA) = 30711
packet_num = 492
len(cAm) = 1536 , len(out_cA) = 29175
packet_num = 493
len(cAm) = 1536 , len(out_cA) = 27639
packet_num = 494
len(cAm) = 1536 , len(out_cA) = 26103
packet_num = 495
len(cAm) = 1536 , len(out_cA) = 24567
packet_num = 496
len(cAm) = 1536 , len(out_cA) = 23031
packet_num = 497
len(cAm) = 1536 , len(out_cA) = 21495
packet_num = 498
len(cAm) = 1536 , len(out_cA) = 19959
packet_num = 499
len(cAm) = 1536 , len(out_cA) = 18423
packet_num = 500
len(cAm) = 1536 , len(out_cA) = 16887
packet_num = 501
len(cAm) = 1536 , len(out_cA) = 15351
packet_num = 502
len(cAm) = 1536 , len(out_cA) = 13815
packet_num = 503
len(cAm) = 1536 , len(out_cA) = 12279
packet_num = 504
len(cAm) = 1536 , len(out_cA) = 10743
packet_num = 505
len(cAm) = 1536 , len(out_cA) = 9207
packet_num = 506
len(cAm) = 1536 , len(out_cA) = 7671
packet_num = 507
len(cAm) = 1536 , len(out_cA) = 6135
packet_num = 508
len(cAm) = 1536 , len(out_cA) = 4599
packet_num = 509
len(cAm) = 1536 , len(out_cA) = 3063
packet_num = 510
len(cAm) = 1536 , len(out_cA) = 1527

I believe this is because the latter parts of the flow graph are blocking, their buffers become full, and this backs up to my source block. This is confirmed by connecting my source block to null sinks, which then allows the source block to run infinitely (well, a long while!).

Is there a way I can slow up this block? I tried using a throttle on the output, but this doesn't help (in fact it seems to make it worse!).

The full code of the block is attached.

Thanks!

David

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