OP25 PCM Underuns When Monitering Motorola SmartZone™ System

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Feb 7, 2021
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Hey again all. I am so close to having my OP25 fully set up, but I am running into one final issue.
I constantly get PCM Underuns when listening to A Motorola SmartZone™ System using multi_rx.py and I dont know why.
Let me know anything you need form me, logs, start command line etc.
Thank all in advanced
 

rlmurray56

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I found this information from @boatbod doing a forum search..........

"PCM underrun means the audio stream stopped coming out of op25 but the PCM (alsa) subsystem expected it to continue. For the most part you can ignore these warnings if they are occasional. If they happen frequently and are accompanied by glitchy audio, it points to signal strength or tuning issues, or hardware with too low a spec."
 
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I found this information from @boatbod doing a forum search..........

"PCM underrun means the audio stream stopped coming out of op25 but the PCM (alsa) subsystem expected it to continue. For the most part you can ignore these warnings if they are occasional. If they happen frequently and are accompanied by glitchy audio, it points to signal strength or tuning issues, or hardware with too low a spec."
Well they do cause audio issues, my thing is that It happens randomly in the middle of audio but any other time it comes through loud and clear, I will attach my signal and constallations
 

boatbod

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The control channel signal looks pretty good, both signal strength and well locked on. What hardware are you running op25 on? Smartzone decode is fairly cpu hungry because it requires two simultaneous channels to be monitored during a voice call. What sdr dongles are you using and what sample rate for each?
 
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The control channel signal looks pretty good, both signal strength and well locked on. What hardware are you running op25 on? Smartzone decode is fairly cpu hungry because it requires two simultaneous channels to be monitored during a voice call. What sdr dongles are you using and what sample rate for each?
Raspberry Pi 3B+
1.2 Ghz Quad Core ARM 7 CPU
1 GB of Ram

Noolec SmartSDR Mini

I dont know where in the config File sample rate would be, sorry. if its the "if_rate" setting then thats gonna be 1800
I JUST got a RPi 4 4 GB so I can try to run it on that instead
 

ww7ch

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A while back I attempted to monitoring a single TG on a P25P2 system using OP25 on an RPI3B+ and had issues. Changed it to an RPI4 and problem solved. I recommend giving it a try...
 
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A while back I attempted to monitoring a single TG on a P25P2 system using OP25 on an RPI3B+ and had issues. Changed it to an RPI4 and problem solved. I recommend giving it a try...
Same Issue, just starts the script faster lol
 

boatbod

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Raspberry Pi 3B+
1.2 Ghz Quad Core ARM 7 CPU
1 GB of Ram

Noolec SmartSDR Mini

I dont know where in the config File sample rate would be, sorry. if its the "if_rate" setting then thats gonna be 1800
I JUST got a RPi 4 4 GB so I can try to run it on that instead
RPi3B is going to be on the edge for a Smartzone system. It will work but you should minimize the sample rate as much as possible.
Assume you are running two RTL dongles or does the system fit entirely within the 2.4Mhz max bandwidth?
Look in the cfg.json file under the "devices" section for the "rate" parameter. If you are using two dongles, suggest going no higher than 1000000.
 
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RPi3B is going to be on the edge for a Smartzone system. It will work but you should minimize the sample rate as much as possible.
Assume you are running two RTL dongles or does the system fit entirely within the 2.4Mhz max bandwidth?
Look in the cfg.json file under the "devices" section for the "rate" parameter. If you are using two dongles, suggest going no higher than 1000000.
I am using two dongles yes, I have now gotten my pi4 set up and am running on that. sample rate is set at the default, I will lower it and report back
 

dave3825

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I attempted to monitoring a single TG on a P25P2 system using OP25 on an RPI3B+ and had issues. Changed it to an RPI4 and problem solved.
P25 Phase 1 and phase 2 run fine on my Pi 3B+. Not one problem with OP25 Boatbod version.
 
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That doesn't actually sound too terrible. Have you tried using pulse audio? (Set the audio device to "pulse" rather than default in the cfg.json file)
Sorry about the gap in response. I tried this and they happen less often but they do still happen. I could excuse it if it didnt cause me to miss conversations.
 

wgbecks

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Sorry about the gap in response. I tried this and they happen less often but they do still happen. I could excuse it if it didnt cause me to miss conversations.
I've been running op25 on the Raspberry Pi 3B, 3B+ and Pi-4B using both rx.py and multi_rx.py and have never had and issues getting PCM underruns. Most typically, I am using the Raspbian Lite versions in a headless stand alone configuration but have also assisted others with op25 on both of the Desktop GUI variants.

If all else fails you might try a fresh Raspbian Buster image and start clean.
 
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