Hi
I’m using the following boot script in order to boot uImage and device tree blob directly from my PC.
No SD card removal, no flashing.
It boots out of RAM immediately
Edit ips and ethernet address accordingly to your network and hardware configuration.
Enjoy

setenv initrd_high 0xffffffff                                                      
setenv fdt_high 0xffffffff
setenv bootargs "root=/dev/mmcblk0p1  rootdelay=10 rw console=ttyS0,115200 panic=10 clk_ignore_unused"
setenv ethaddr D2:91:80:B7:AB:5C
setenv serverip 192.168.1.147
setenv ipaddr 192.168.1.145
ext4load mmc 0 0x43000000 boot/script.bin
tftp 0x49000000 sun7i-a20-cubieboard2.dtb
tftp 0x46000000 uImage
bootm 0x46000000 - 0x49000000