What is the difference between ARCH_XXX MACH_XXX TARGET_XXX macros

[Tim Williams]

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