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[Discuss-gnuradio] How to control the open and close state of a flow gra

From: Zhonghua
Subject: [Discuss-gnuradio] How to control the open and close state of a flow graph
Date: Tue, 07 Feb 2012 15:51:17 +0100
User-agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv: Gecko/20110921 Thunderbird/3.1.15

Hi every one,

I am trying to control the open and close state of the flow graph which implements transmission and receiving tasks. I would not like to use start() and stop() pair to do that because the construction time is too long. What I expect is sending a signal from another process to control the flow graph of local process. The architecture is very simple. In RX channel, Using uhd.usrp_source() to get flow and transferring it to a signal process block for example ieee802_15_4_demod_pkts(). TX part transferring flow from ieee802_15_4_mod_pkts to uhd.usrp_sink(). The RX and TX are put in two separate top_block and control them respectively. The simplest method I used to control is lock() and unlock(). My scenario is that when signal A arrived , call lock(), then when signal B arrived call unlock() to revive the flow. The result is sometimes in the period of signal A the flow does not stop and there is still data transferred from usrp_source to demod_pks block. Then, I try to use method that combines lock() + disconnect()+unlock() to stop the flow. For reviving the flow, lock()+connect()+unlock() is used. The result is identical with the former experiment. At last I realised maybe the usrp_source is two slow so it block the signal handler's action. To verify it, I added the period of signal B to give adequate time for the data transferring from usrp_source to the demod_pkts(). I found the signal handler's action became almost regular. If I came back to the old time configuration but set a lower sample rate of the uhd.usrp_source(), the signal handler's action also became regular. So now my question is if I have to keep a small period of signal B and simultaneously a relatively high sample rate, how can I control the flow? Are there some approaches to mute the usrp_source thoroughly at the period of signal B?
Any suggestion is highly appreciated.



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