1Here is the step-by-step to boot to U-Boot on rk3368.
2
3Get miniloader and trust.img form rockchip vendor u-boot source code
4==============================================================================
5  > git clone  https://github.com/rockchip-linux/u-boot.git rockchip-uboot
6  > cd rockchip-uboot
7  > make rk3368_defconfig /*chose px5_defconfig if you run a px5 platform here*/
8  > ./mkv8.sh
9
10Compile the upstream U-Boot
11===========================
12  > cd u-boot
13  > make CROSS_COMPILE=aarch64-linux-gnu- sheep-rk3368_defconfig  all
14
15Package u-boot for miniloader
16================================
17  > ../rockchip-uboot/tools/loaderimage --pack --uboot u-boot.bin u-boot.img
18
19Flash the image by rkdeveloptool
20================================
21rkdeveloptool can get from https://github.com/rockchip-linux/rkdeveloptool.git
22
23Power on(or reset with RESET KEY) with MASKROM KEY preesed, and then:
24  > rkdeveloptool db ./rockchip-uboot/rk3368_loader_v2.00.256.bin
25  > rkdeveloptool wl 0x6000 ./rockchip-uboot/trust.img
26  > rkdeveloptool wl 0x4000 ./u-boot/u-boot.img
27  > rkdeveloptool RD
28
29You should be able to get U-Boot log message from boot console:
30
31U-Boot 2017.05-rc3-01094-g9ddd1e8-dirty (May 15 2017 - 15:57:23 +0800)
32
33Model: Rockchip sheep board
34DRAM:  2 GiB
35MMC:   dwmmc@ff0f0000: 0
36Using default environment
37
38In:    serial@ff690000
39Out:   serial@ff690000
40Err:   serial@ff690000
41Net:   Net Initialization Skipped
42No ethernet found.
43Hit any key to stop autoboot:  0
44=>
45