什么是 nx_ type

nx_ types 是在nesC 1.2，tinyos中用到的platform independent types. 这个类型的数据可以适用任何平台。

To accomplish this goal, nesC 1.2 introduces platform independent types.（network types）

Platform independent simple types (integers) are either big-endian or little-endian, independently of the underlying chip hardware.

Generally, an external type is the same as a normal type except that it has nx preceding it

nx_uint16_t val; // A big endian 16-bit value
nxle_uint32_t otherVal; // A little endian 32-bit value

nx_types is that they were introduced to deal with what does a packet looks like on the wire.  It deals with both the packing problem as well as endianess.  The end result of nx_types must be by definition be platform independent, thats the whole point.  The implementation must also be by definition be platform dependent because the intent is nx_types marry a given platform to network order so data packets can make sense across different machines and the right thing still happens.

platform independent structs, declared with nx struct