JTAG and SystemC are both IEEE standards (1149.1 and 1666 respectively), and the standardization documents are the ultimate reference. The SystemC standard [5] is a free PDF download (a novelty for the IEEE), but the JTAG standard [3] costs money. The Texas Instruments JTAG primer [4] is a useful free alternative.

The files making up the reference implementation for the JTAG SystemC interface are comprehensively commented, and can be processed with Doxygen [1]. Each class, member and methods behavior, parameters and any return value is described.