# Hier signal processing block in Python **URL:** \ **Category:** GNU Radio\ **Created:** [January 24, 2013, 5:22pm UTC](https://www.ruby-forum.com/t/hier-signal-processing-block-in-python/225707 "2013-01-24T17:22:13Z")\ **Posts on this page:** 3\ **Page:** 1
**Author:** ![aris](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/258eb7/32.png) [@aris](https://www.ruby-forum.com/u/aris)\ **Post date:** [January 24, 2013, 5:22pm UTC](https://www.ruby-forum.com/t/hier-signal-processing-block-in-python/225707/1 "2013-01-24T17:22:13Z")
Hi all, Can somebody explain me a bit the difference between blocks written in python in the way presented on the website and blocks like packet decoder, packet encoder, gfsk modulator, etc. The latter blocks are written also in Python, but they are different than the previous. Particularly I don’t understand why there are also thread classes stick to the blocks from the second group. And the most important thing is I would like to know how to make such block out of tree. Many thanks ---
**Author:** ![Nemanja\_S](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/n/7bcc69/32.png) [@Nemanja\_S](https://www.ruby-forum.com/u/Nemanja_S)\ **Post date:** [January 24, 2013, 7:26pm UTC](https://www.ruby-forum.com/t/hier-signal-processing-block-in-python/225707/2 "2013-01-24T19:26:46Z")
On 01/24/2013 10:20 AM, Nemanja S. wrote: > Hi all, > > Can somebody explain me a bit the difference between blocks written in > python in the way presented on the website and blocks like packet decoder, > packet encoder, gfsk modulator, etc. The latter blocks are written also in > Python, but they are different than the previous. Particularly I don’t > understand why there are also thread classes stick to the blocks from the > second group. Those old blocks are just hier blocks with some processing blocks from gnuradio, where the python interface part is outside of the scheduler, really just a python thread polling a message queue. The interface is a python function call or something. So, there are APIs to create blocks in python that actually use the scheduler. For example, here is one that does the pkt framer/correlate but presents a message interface. This block has inputs and outputs that can be connected in a gnuradio flow graph. > Then you can do cool things like this: [https://github.com/jmalsbury/pre-cog/wiki](https://github.com/jmalsbury/pre-cog/wiki) > And the most important thing is I would like to know how to make such block > out of tree. Most of the feature above is in gnuradio master branch, but I dont think there is a doc, so you will have to interpolate from this: > **[Blocks Coding Guide](https://github.com/guruofquality/grextras/wiki/Blocks-Coding-Guide)** > > Advanced GNU Radio Blocks. Contribute to guruofquality/grextras development by creating an account on GitHub. -josh ---
**Author:** ![Nemanja\_S](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/n/7bcc69/32.png) [@Nemanja\_S](https://www.ruby-forum.com/u/Nemanja_S)\ **Post date:** [January 24, 2013, 11:19pm UTC](https://www.ruby-forum.com/t/hier-signal-processing-block-in-python/225707/3 "2013-01-24T23:19:23Z")
Thank you Josh, I hope your answer will help. The problem particularly with packet decoder block which could be found in packet.py is that I can’t figure out how messages goes from framer sink to the message source. Namely, framer sink sends message to the queue. There is a thread responsible for reading message from the queue and for calculating crc. After that, callback function is called and if message was OK, it will post message again to the queue (Isn’t there only one queue between two blocks and both read from and write to that queue?). By the way, do you think that message source sounds like block which produces messages (that’s what i was thinking at first glance, but maybe cause I am not native speaker)? Cheers