source:

rtk-hciattach.service: 
https://github.com/revyos/mkimg-th1520/blob/main/addons/etc/systemd/system/rtk-hciattach.service
rtk_hciattach:
https://github.com/revyos/mkimg-th1520/blob/main/addons/lpi4a-bt/rootfs/usr/local/bin/rtk_hciattach

thanks revy.