What is the difference between ARCH_XXX MACH_XXX TARGET_XXX macros

Hello, I am trying to port u-boot to a new board,

There are several macros, how to use them properly?

CONFIG_ARCH_XXX CONFIG_MACH_XXX CONFIG_TARGET_XXX

for example, my board has:

SoC: LS2K1000 ISA: MIPS32r1, MIPS32r2, MIPS64r1, MIPS64r2 Board: UselessRouter or HelloRouter, TBD NIC: 4 1000Mbps NIC(No built in switcher)

thanks very much!

Regards, Tim