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Setting up OpenWebRX on a Raspberry Pi 2

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András Retzler edited this page Aug 15, 2018 · 36 revisions

OpenWebRX should work out of the box on your RPi, if you set it up by going through this guide.

You will need at least a Raspberry Pi 2.

Raspberry Pi 1 won't work as its CPU just doesn't have enough processing capability to make it.

(csdr can make use of both NEON and the multiple cores on the RPi2).

As noted by Zsolt, HG2ECZ the Raspberry Pi 3 can limit the CPU frequency if the maximum available current of the power supply is too low, which may result in decreased signal processing speed. Having a correct power supply is required for running OpenWebRX. An 5V, 2A unit (or better) should do.

Common issues with the RPi 2

It is not sure that you will run into any of these, but anyway:

  • Audio underruns and csdr flowcontrol issue
  • Port 8888 is already in use on your system:
    • Edit config_rtl.py and config_webrx.py and replace this port number with another).
  • The Pi doesn't start with RTL-SDR is plugged in / restarts when plugging in RTL-SDR / fails to recongize RTL-SDR:
    • Maybe your power supply cannot provide enough current. You should try a dedicated 5V / 2A power supply like this. I wasn't able to use the RPi from a laptop USB port, needed a dedicated PSU.

Compromise between performance and the maximum number of clients

The Raspberry Pi 2 should be able to handle about 5-10 clients simultaneously at the sampling rate of 250 ksps.

It is quite good from an embedded ARM board, but your PC would do of course better than that.

I'm constantly working on getting OpenWebRX faster on the Pi (in the dev branch I've already done some manual assembly optimizations for NEON).

You will have to set the max_clients and the samp_rate correctly. If you allow too much clients to connect, audio will lag for all of them (will get audio underruns), as the CPU just can't make it.

The higher the sampling rate is:

  • the higher bandwidth will be seen on the waterfall diagram,
  • the higher the CPU usage gets (per client as well),
  • the less clients can connect without lags.

You should try to open many browser windows and see at how many clients will the audio start to lag.

Some general advice to increase reliability and security

Use a firewall

If you don't want to learn iptables, you can use ufw on Debian/Ubuntu based systems. ufw stands for Uncomplicated Firewall. After ufw has been started, it will block any incoming TCP connections / UDP packets unless specifically enabled.

(This part is to be finished.)

Put sshd away from TCP port 22

(This part is to be done.)

Avoid possible file system corruption on power-off

If you just pull the plug from your Raspberry without properly shutting it down, it may or may not boot the next time.

1. Shutdown the RPi with halt every time

Use the proper command to halt the operating system:

sudo halt

You will see one of the LEDs blinking at a given time interval, and then both LEDs switch off.

2. Start your system in read-only mode, and switch to read-write only if required.

In my article about pi-rw you will find advice on doing that.

3. What if my file system has already corrupted?

fsck is a Linux tool meant for repairing corrupted file systems.

You can:

  • Run fsck from a laptop running Linux, having the SD card attached.
  • Run fsck from a Ubuntu Live CD.
  • Run fsck from the shell over the RPi serial port (but you will need a serial adapter).
  • Run fsck with a keyboard and HDMI screen attached to the RPi.

You cannot however run fsck from ssh remotely, as the OS hasn't booted properly yet.

First take a look at which device corresponds to your SD card. You can list the block devices with lsblk:

ha7ilm@pc ~ $ lsblk
NAME        MAJ:MIN RM   SIZE RO TYPE MOUNTPOINT
sda           8:0    0 123,4G  0 disk 
├─sda1        8:1    0 120,0G  0 part /
└─sda2        8:2    0   3,4G  0 part [SWAP]
mmcblk0     179:0    0   7,4G  0 disk 
├─mmcblk0p1 179:1    0    56M  0 part /media/ha7ilm/boot
└─mmcblk0p2 179:2    0   7,4G  0 part /media/ha7ilm/18b2d310-8421-01f9-a0e0-1001b0d00173

Over here, the corresponding device is mmcblk0p2. To run fsck on it:

sudo fsck /dev/mmcblk0p2
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