VxWorks gives the programmer access to a library of symbol table support routines and provides a global symbol table which contains all external variable and function references in the system. The device support modules described here allow selected record types to read and write variables referenced by name. Device support has been provided for ai, ao, longin, longout, stringin, stringout and waveform record types. An underscore is automatically prefixed. Suffixes and prefixes are optional.
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In this version of the driver, the value of the pointer is read at run-time rather than initialisation. Finally note that strings are not treated any differently from longs or doubles in that the address returned from this routine is simply the address of the data. Processing consists of reading or writing the VAL field using the pointer, unless the pointer is NULL, in which case the device support module exits immediately. String operations are restricted to the 40 character size of the string record VAL fields and null termination is enforced. No exclusion or interlocking with other code using the referenced variable is provided.