I have been working on and off on PBP Ethernet, and it's not easy. And not friendly, at all. Base of my work is article from Nuts and Volts, and building from there using various examples from net.
But one thing that surprises me a lot is that PBP is much more efficient than C. Lot less typing to do same thing, and as far as I can see much smaller code. But very little additional stuff you can put in 128K...