Embedding the Internet: Squeezing TCP/IP into an 8-Bit Micro-Controller
Christopher Jf Waters · 1999
As the ubiquity of the Internet increases there is a demand to make more devices Internet friendly. This means pushing resource limits to create TCP/IP network stacks for smaller and cheaper embedded processors. This paper describes the experience of the author in developing a TCP/IP stack to enable a web server in an extremely resource constrained 8-bit micro-controller. The micro-controller in question is from the Scenix SX series and has 256 bytes of RAM and 4K words of program memory. This device was chosen because of its small physical size coupled with a relatively high computational power (50 MIPS at 5OMH2). A usable TCP/IP network stack requires several protocols to be implemented: TCP, IP and ICMP. A UDP implementation was also developed for use in simpler command and control applications. For the physical interface both the Point-to-Point Protocol (PPP) and IEEE 802.3 Ethernet have been implemented. Fitting the network stack into such a resource constrained device has necessitated several tradeoffs and limitations. However, a key requirement was that the stack be RFC compliant and inter-operate with any other TCP/IP implementation. This paper describes where the tradeoffs were made, why they were made and how RFC compliance was maintained.