For an embedded Linux system, if I have two or more network interfaces, how do I ensure that they always get the same interface names every boot

In other words, I want, for example, eth0 to always map to one physical Ethernet port, eth1 to the next, etc.

My Linux "distribution" is home-grown, and I use devtmpfs for populating /dev. I use busybox for init (and most everything else), along with custom init scripts for system startup and shutdown.

I do not need hotplug facilities of mdev or udev -- I'm referring to "fixed" Ethernet ports.