Rough instructions for now. Will clean up later.
https://wiki.alpinelinux.org/wiki/Raspberry_Pi
/media/mmcblk0p1/userconfig.txt
dtparam=audio=off dtparam=i2c_arm=on dtparam=i2c1=on dtoverlay=i2c-rtc,ds3231 dtparam=spi=off enable_uart=1 dtoverlay=disable-wifi dtoverlay=disable-bt dtoverlay=pps-gpio,gpiopin=4 dtparam=act_led_trigger=heartbeat
Additional Steps:
/dev/mmcblk0p2 /data ext4 rw,relatime 0 0
apk add git build-base scons asciidoctor libxslt docbook-xsl python3-dev libcap-dev ncurses-dev
cd /data wget https://github.com/redlab-i/pps-tools/archive/refs/tags/v1.0.2.tar.gz tar zxvf v1.0.2.tar.gz ; cd pps-tools-1.0.2/ ; make (as root) make install ppstest /dev/pps0