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:

• Create a non-root user
• Install and enable dropbear/openssh
• Create ext4 partition with the rest of the SD space, mount at /data

  /dev/mmcblk0p2 /data ext4 rw,relatime 0 0

• Install dependencies

  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