Totally get and applaud that. Indeed, I built a high-performance Ethernet driver for the STM32F4 chips just because I wanted to say I've done it. But his stat

Totally get and applaud that. Indeed, I built a high-performance Ethernet driver for the STM32F4 chips just because I wanted to say I've done it. But his stated goal is to build a TCP/IP stack, not futz around with SPI and the particulars of an idiosyncratic network chip. There will be plenty of work (and learning) to do once he starts climbing up the network stack.