OK, I've been stabbing in the dark on the OS all day, but I think I have it now. No, really. Really.
Check out this Atheros Bulletin. Atheros provides eCos for the ar6001 chips and they call it "eCOS BSP - Basic Kernel." There are references to the "BSP version AR6000-..." in the firmware *and* eCos has a 'devfs'. Then, there's this post from Berend about using lwIP with eCos.
Any eCos hackers out there?