"put u-boot into ram and start it"?

Hi, dear Forum,

I am flashing OpenWrt into EasyBox 803 - openwrt.org/toh/astoria/arv752dpw22#installing_openwrt
(section #Install OpenWrt via serial port)
So I've done the part "cat ARV752DPW22_boot.dump openwrt-lantiq-danube-ARV752DPW22-squashfs.image > flash.img" and sx flash.img </dev/ttyUSB0 >/dev/ttyUSB0

and then "put u-boot into ram and start it"? What exactly to do?

Thank you in advance.

Isn't that the bootm command, in uboot?

Type help while in uboot.