ALSA support

[tmigone]

Device sound cards will be preconfigured and exposed to pulseaudio for supported devices with no extra configuration needed.

Raspberry Pi 3:

• Audio jack
• HDMI

Raspberry Pi 4:

• Audio jack
• HDMI0
• HDMI1

[tmigone]

Raspberry Pi

snd_bcm2835 kernel module has two modes of operation:

1. without parameters, it will create a single ALSA card (aplay -l) with two/three different "devices". You can switch between them using amixer cset numid=3 x.

2. using parameters: snd_bcm2835.enable_headphones=1 snd_bcm2835.enable_hdmi=1 snd_bcm2835.enable_compat_alsa=0. It will create two/three different cards.

Considerations

• Mode 2 allows you to have one pulse sink for each output (HDMI0/HDMI1/3.5mm) which is what we want because standarization is good! (pactl load-module alsa-sink device=hw:CARD=HDMI,DEV=0)
• Mode 2 is not the default module configuration. So enabling it requires either editing cmdline.txt or modprobe-ing the module on startup.
• Mode 1, pulseaudio overrides the default amixer card so amixer cset numid=3 x needs to be amixer -c 0 cset numid=3 x.
• Mode 2 removes the need of installing alsa-utils package which can spur confusion.

Neat bash commands to get kernel module parameters:

cat /proc/modules | cut -f 1 -d " " | while read module; do \
 echo "Module: $module"; \
 if [ -d "/sys/module/$module/parameters" ]; then \
  ls /sys/module/$module/parameters/ | while read parameter; do \
   echo -n "Parameter: $parameter --> "; \
   cat /sys/module/$module/parameters/$parameter; \
  done; \
 fi; \
 echo; \
done

[tmigone]

Reopening to further evaluate in the future...