Buildroot configuration to turn a raspberry pi into a dumb mp3 player
Clone buildroot's git repository,load rpi's config file and modify it
git clone https://github.com/buildroot/buildroot
cd buildroot
make raspberrypi_defconfig
make menuconfig
Select configuration options.
Toolchain -- > enable WCHAR support
System configuration --> root filesystem overlay directories (overlay)
System configuration --> /dev management (Dynamic using devtmpfs + eudev)
Target packages --> audio and video --> alsa-utils
Target packages --> audio and video --> mpg123
Target packages --> filesystem and flash utilities --> exfatprogs
Target packages --> filesystem and flash utilities --> ntfs-3g
Target packages --> Hardware handling --> enable hwdb installation
Filesystem images --> initial RAM filesystem linked into linux kernel
Create a folder named "overlay" with our customizations. This file sets the headphones as default audio output.
/etc/asound.conf
defaults.pcm.card 1
defaults.ctl.card 1
This script loads the soundcard module, mounts the pendrive, creates a playlist and starts playing.
/root/start.sh
modprobe snd-bcm2835
mkdir -p /media/musika
mount /dev/sda1 /media/musika -o ro
find /media/musika/ -name "*.mp3" > /tmp/lista.m3u
mpg123 -@ /tmp/lista.m3u
This file is a copy of the original inittab, but replaces the login console with the previous script.
/etc/inittab
...
#tty1::respawn:/sbin/getty -L tty1 0 vt100 # HDMI console
tty1::respawn:-/bin/sh /root/start.sh
...
Soundcard is disabled by default so we have to enable it. Add a line at the end of file.
board/raspberrypi/config_default.txt
...
dtparam=audio=on
hdmi_force_hotplug=1
...
Second line forces video output through hdmi. Without that option, if there is no hdmi screen attached the board outputs audio AND VIDEO through jack (so we can use 3.5mm auxiliary to composite cables).
I want to run the system in ram, so uncomment this line too.
board/raspberrypi/config_default.txt
...
#initramfs rootfs.cpio.gz
initramfs rootfs.cpio.gz
...
Modify this file to add rootfs.cpio.gz to our image, and change the size to 64M (original is 32M).
board/raspberrypi/genimage-raspberrypi.cfg
image boot.vfat {
vfat {
files = {
"bcm2708-rpi-b.dtb",
"bcm2708-rpi-b-plus.dtb",
"bcm2708-rpi-cm.dtb",
"rpi-firmware/bootcode.bin",
"rpi-firmware/cmdline.txt",
"rpi-firmware/config.txt",
"rpi-firmware/fixup.dat",
"rpi-firmware/start.elf",
"rootfs.cpio.gz",
"zImage"
}
}
size = 64M
}
...
Run the project
make
Special thanks to
https://marcocetica.com/posts/buildroot-tutorial/
https://www.raspberrypi.com/news/latest-raspberry-pi-os-update-may-2020/
I wanted to control the mp3 player but didn't want to use a full keyboard so plugged this keypad and configured it
https://www.amazon.es/gp/product/B00VQ3DR1E
First I found the vendor's code with lsusb (13ba)
lsusb
Bus 001 Device 014: ID 13ba:0001 PCPlay Konig Electronic CMP-KEYPAD12 Numeric Keypad
Then I found it's modalias
find /sys -name *modalias | xargs grep -i 13ba
/sys/devices/pci0000:00/0000:00:1a.0/usb1/1-1/1-1.2/1-1.2:1.0/0003:13BA:0001.0004/input/input22/modalias:input:b0003v13BAp0001e0110-e0,1,4,11,14,k71,72,73,74,75,77,79,7A,7B,7C,7D,7E,7F,80,81,82,83,84,85,86,87,88,89,8A,B7,B8,B9,BA,BB,BC,BD,BE,BF,C0,C1,C2,F0,ram4,l0,1,2,sfw
Finally got the key codes with evtest
evtest
Event: time 1651002716.523273, type 4 (EV_MSC), code 4 (MSC_SCAN), value 7005d
Event: time 1651002716.523273, type 1 (EV_KEY), code 76 (KEY_KP5), value 1
...
And wrote the configuration file
/etc/udev/hwdb.d/numkeypad.hwdb
evdev:input:b0003v13BAp0001*
KEYBOARD_KEY_7005d=s
KEYBOARD_KEY_7005c=d
KEYBOARD_KEY_7005e=f
KEYBOARD_KEY_70060=leftbrace
KEYBOARD_KEY_7005a=rightbrace
KEYBOARD_KEY_70054=comma
KEYBOARD_KEY_70055=dot
Thanks to
https://askubuntu.com/questions/742946/how-to-find-the-hwdb-header-of-a-general-input-device
https://www.rigacci.org/wiki/doku.php/doc/appunti/linux/sa/remap_keyboard_keys
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