To add the package to OpenWrt Build System append
src-git usbtemp https://github.com/usbtemp/opkg-packages.git
to feeds.conf, or execute
echo "src-git usbtemp https://github.com/usbtemp/opkg-packages.git" >>feeds.conf
in buildroot (source) directory.
Then update feeds by running
./scripts/feeds update
./scripts/feeds install -a -p usbtemp
Finally, enable package utmp-cli (under Utilities) in make menuconfig (sufficient only as a module) and compile package as
make package/feeds/usbtemp/utmp-cli/compile
Openwrt package (ipk) is created in bin/packages/__target_arch__/usbtemp/ directory.
Instead of running menuconfig the package could be marked as module by:
echo "CONFIG_PACKAGE_utmp-cli=m" >> .config
make oldconfig
Digitemp package is available in official OpenWrt package repository.