准备工作：
uboot下载：ftp://ftp.denx.de/pub/u-boot/u-boot-2018.07.tar.bz2
toolchain下载：http://releases.linaro.org/components/toolchain/binaries/7.3-2018.05/aarch64-linux-gnu/gcc-linaro-7.3.1-2018.05-x86_64_aarch64-linux-gnu.tar.xz
arm-trusted-firmware（编译bl31.bin）下载：https://github.com/apritzel/arm-trusted-firmware/tree/cd7fa4893dd204e419a8403a8d1dc1c295e3d698
编译工作：
第一步：进入arm-trusted-firmware文件夹编译uboot用到的bl31.bin文件(原因请百度or谷歌or参考：uboot/board/sunxi/README.sunxi64)
$ export CROSS_COMPILE=aarch64-linux-gnu-
$ make PLAT=sun50iw1p1 DEBUG=1 bl31执行完上述指令后会在 arm-trusted-firmware/build/sun50iw1p1/debug文件夹中生成bl31.bin
注意：最新的arm--trusted-firmware没有sun50iw1p1平台，所以我用的老的（上边的地址）
第二步：将第一步生成的bl31.bin文件拷贝到uboot根目录下
第三步：编译uboot
$ export CROSS_COMPILE=aarch64-linux-gnu-
$ make orangepi_pc2_defconfig
$ make执行完上述指令后在uboot根目录下生成：u-boot-sunxi-with-spl.bin文件
第四步：下载uboot到SD卡
$ sudo dd if=u-boot-sunxi-with-spl.bin of=/dev/sdx bs=8k seek=1注意：上述指令 of=/dev/sdx 中的 sdx 根据你自己的环境替换，我的环境是sdb
第五步：将SD卡插入开发板测试
打印如下信息：
U-Boot SPL 2018.07 (Aug 07 2018 - 18:02:30 +0800)
DRAM: 1024 MiB
Trying to boot from MMC1
NOTICE: BL3-1: Running on H5 (1718) in SRAM A2 (@0x44000)
NOTICE: Configuring SPC Controller
NOTICE: BL3-1: v1.0(debug):4fe12b7
NOTICE: BL3-1: Built : 17:31:07, Aug 7 2018
NOTICE: PLL_CPUX: 90001521
INFO: BL3-1: Initializing runtime services
INFO: BL3-1: Preparing for EL3 exit to normal world
INFO: BL3-1: Next image address: 0x4a000000, SPSR: 0x3c9
U-Boot 2018.07 (Aug 07 2018 - 18:02:30 +0800) Allwinner Technology
CPU: Allwinner H5 (SUN50I)
Model: OrangePi PC 2
DRAM: 1 GiB
MMC: SUNXI SD/MMC: 0
Loading Environment from FAT... *** Warning - bad CRC, using default environment
Failed (-5)
In: serial
Out: vidconsole
Err: vidconsole
Allwinner mUSB OTG (Peripheral)
Net: phy interface7
eth0: ethernet@1c30000
Warning: usb_ether using MAC address from ROM
, eth1: usb_ether
starting USB...
USB0: USB EHCI 1.00
USB1: USB OHCI 1.0
USB2: USB EHCI 1.00
USB3: USB OHCI 1.0
scanning bus 0 for devices... 1 USB Device(s) found
scanning bus 2 for devices... 1 USB Device(s) found
scanning bus 1 for devices... 1 USB Device(s) found
scanning bus 3 for devices... 2 USB Device(s) found
scanning usb for storage devices... 0 Storage Device(s) found
Hit any key to stop autoboot: 2 1 0