Note that the data in initrd can have any structure
in this case and doesn't necessarily have to be a file system image.

Compressed cpio images
----------------------

Recent kernels have support for populating a ramdisk from a compressed cpio
archive. On such systems, the creation of a ramdisk image doesn't need to
involve special block devices or loopbacks; you merely create a directory on
disk with the desired initrd content, cd to that directory, and run (as an
example):

find . | cpio --quiet -H newc -o | gzip -9 -n > /boot/imagefile.img

Examining the contents of an existing image file is just as simple:

mkdir /tmp/imagefile
cd /tmp/imagefile
gzip -cd /boot/imagefile.img | cpio -imd --quiet

простенький спикер (как в обычном pc).
Понимаю что можно его подключить к gpio