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).

v2pro/     - Architectural files for the Xilinx Virtex-II PRO device with 
             embedded PowerPC 405 Processor.  Supports lwIP Raw API only.
             (requires V2PDK - http://www.xilinx.com/ise/vii_pro/kit.htm)

msvc6/     - Architectural files for Microsoft Visual C++ 6.0

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.

include/   - Architectural specific header files.

netif/     - Architectural specific network interfaces.