Get Ralink SDK, filename: MTK_Ralink_ApSoC_SDK_4120_20120607.tar.bz2
Unpack the "toolchain/buildroot-gcc342" folder to "/opt/buildroot-gcc342", or wherever you want, but then you need to replace the paths below.
$ git clone git@github.com:agustim/u-boot_wrtnode.git
$ export CONFIG_CROSS_COMPILER_PATH=/opt/buildroot-gcc342/bin # necessary if not in /opt
$ export PATH=/opt/buildroot-gcc342/bin:$PATH
$ cp wrtnode_config .config
$ make menuconfig # Exit and save
$ make
$ hexdump -C uboot.bin | head # look at first bytes to verify
NOTE: The output filename for directly flashing the binary has to be uboot.bin.
The first bytes of uboot.bin are some sort of interrupt vector table and should look approximately like this (exact address entries may vary):
00000000 ff 00 00 10 00 00 00 00 fd 00 00 10 00 00 00 00 |................|
00000010 7f 02 00 10 00 00 00 00 7d 02 00 10 00 00 00 00 |........}.......|
00000020 7b 02 00 10 00 00 00 00 79 02 00 10 00 00 00 00 |{.......y.......|
00000030 77 02 00 10 00 00 00 00 75 02 00 10 00 00 00 00 |w.......u.......|
00000040 73 02 00 10 00 00 00 00 71 02 00 10 00 00 00 00 |s.......q.......|