Adding Alsa Loopback Interface before build

olafzen · September 11, 2026 at 5:41 PM

Hello,

I tried to compile LE 12.2.1 with the option to use an Alsa loopback Interface.

I changed the Kernel config file (CONFIG_SND_ALOOP=m) first before the make image process.

But the modul has not been build, when compiling finished.

How is it possible, to build LE with the apropriate aloop modul? Either fixed in kernel or as a modul?

FYI; I want to use camilladsp with my LE Box (PI4b) and therefore I need a loopback interface.

Thanks in advance.

Best regards

Olaf

olafzen · September 12, 2026 at 8:24 AM

Nevermind,

I've read the GIT Wiki and will try that way (cloning, forking, editing and commiting...).

Is this the right way:

In my forked Git clone; edit /projects/RPi/devices/RPi4/linux/linux.aarch64.conf (add CONFIG_SND_ALOOP=m)

Add the changed file to the forked repo:

git add projects/RPi/devices/RPi4/linux/linux.aarch64.conf

Download sources:

PROJECT=RPi ARCH=aarch64 DEVICE=RPi4 tools/download-tool

Start build process:

PROJECT=RPi ARCH=aarch64 DEVICE=RPi4 make image

Test the new image. Check if the loopback module exists and loads (modprobe snd-aloop)

If succesfull:

git commit -m "linux: enable Alsa Loopback Interface"

???

**chewitt** · September 12, 2026 at 10:13 AM

If you have a working default image building, edit projects/RPi/devices/RPi4/linux/linux.aarch64.conf to enable the module then rebuild the image and it will rebuild the kernel and update the image.

At least that's the theory. It doesn't work for me on an Amlogic image with linux-7.3-rc2 kernel either, and diff comparing the edited conf and .config file from the kernel build folder shows the kernel has unset CONFIG_SND_ALOOP=m when processing the config; hence nothing gets built.

I will task Claude to investigate the problem once I take a break from some other debugging. I suspect some kind of upstream kernel issue and not something on our side.

**HiassofT** · September 12, 2026 at 10:34 AM

You also need CONFIG_SND_DRIVERS=y

so long,

Hias

**chewitt** · September 12, 2026 at 10:56 AM

Code

config SND_ALOOP                                                                          
        tristate "Generic loopback driver (PCM)"                                          
        select SND_PCM                                                                    
        select SND_TIMER                                                                  
        help                                                                              
          Say 'Y' or 'M' to include support for the PCM loopback device.                  
          This module returns played samples back to the user space using                 
          the standard ALSA PCM device. The devices are routed 0->1 and                   
          1->0, where first number is the playback PCM device and second                  
          number is the capture device. Module creates two PCM devices and                
          configured number of substreams (see the pcm_substreams module                  
          parameter).                                                                     
                                                                                          
          The loopback device allows time synchronization with an external                
          timing source using the time shift universal control (+-20%                     
          of system time).                                                                
                                                                                          
          To compile this driver as a module, choose M here: the module                   
          will be called snd-aloop.

Display More

No mention of SND_DRIVERS there ^ so looks like a kernel bug to report and submit a fix for

**HiassofT** · September 12, 2026 at 11:02 AM

Scroll up a bit and you'll notice it's inside a if SND_DRIVERS block

linux/sound/drivers/Kconfig at master · torvalds/linux

Linux kernel source tree. Contribute to torvalds/linux development by creating an account on GitHub.

github.com

so long,

Hias

**chewitt** · September 12, 2026 at 11:05 AM

"User error: please replace user"

olafzen · September 12, 2026 at 11:37 AM

Ah OK, thanks for replies.

I guess the missing driver entry was the culprit in my 1st. attempt

Will give it a try.

olafzen · September 13, 2026 at 12:19 PM

Cool, it works..

Now I need to start 2 applications (camillagui and camilladsp) as a service and load snd-aloop bofore this services.

Therefor I have to define 3 new services under /storage/.config/system.d/, correct?

Thanks for your support.

**chewitt** · September 13, 2026 at 1:10 PM

I’d build the module with =y so it’s always present and doesn’t need to be loaded. Use two services for the apps if you need to manage start order. Or do in one if they can start more in parallel. Or use one and put whatever sequence you need in a script and execute that from a service. Lots of options; probably no wrong or right and to the question

olafzen · September 13, 2026 at 3:18 PM

Unfortunately I did a make clean ... Oh, and recompiling takes ONLY several hours on the PI4 .

But no Problem, I created the relevant services. It runs like a charm now.

The loop module is loaded by a service and then Camilladsp (CDSP) and camillagui.

Next step is remote control of volume for CDSP. CDSP is controlled over Python Websocket.

It means, I have to put the relevant Python modules into the build tree... Duh..

Let's see

**chewitt** · September 13, 2026 at 3:27 PM

Once complexity reaches a certain point it's time to look for a Docker container that a) has everything needed, b) is attentively maintained by someone else

olafzen · September 13, 2026 at 4:21 PM

Haha someone else...

The thing is, there's a complete separate python environment with all the needed modules within camillagui_backend. If only I could use them and control parts with flirc events...

I'll ask in the diyaudio forum.

So for here; case closed.

Merci bien.