The software doesn't use any operating system. Everything is implemented from scratch. Some of the API's (e.g. timer API) are modelled after the corresponding Linux kernel API's. However, this does not imply that any of the actual implementation is shared. The reason for matching the Linux API's is merely because they are well-understood and there's lots of example code using them. The SAM7 firmware is compiled using GNU GCC 4.0.2 for ARM. It uses GNU Make for processing the Makefiles. All development of the system happened on Linux, therefore your milage of compiling it on Windows might vary, but should theoretically work.