Compile kernel for popmetal:
export ARCH=arm export CROSS_COMPILE=/path/to/your/toolchain/...
make zImage
make rk3288-popmetal.dtb
cat arch/arm/boot/zImage arch/arm/boot/dts/rk3288-popmetal.dtb > arch/arm/boot/kernel
./mkkrnlimg arch/arm/boot/kernel kernel.img
then Download the kernel.img to your board.