6502/      - Architectural files for the 6502 CPU.

rtxc/      - Architectural files for the RTXC operating system.

unix/      - Architectural files for testing on unix-like systems
             (assuming gcc and pthreads).

Each subdirectory (may) also include:

perf.c     - Optional file that should be implemented when running
             performance tests of lwIP.

sys.c      - Implementation of the operating system emulation layer.

netif/	   - Architectural specific network interfaces.