nxtOSEK is an RTOS for LEGO Mindstorms NXT. nxtOSEK consists of I/O driver part of LEJOS NXJ, TOPPERS/ATK1 RTOS, and glue code for them. You can write applications for NXT in ANSI-C/C++. Check nxtOSEK site: http://lejos-osek.sourceforge.net
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