The constructor simply initializes the private data fields to default values (type RESET, bit size zero, debugging disabled).

The two virtual methods which must be implemented, clone and copy_from use boilerplate code from the TLM 2.0 language reference manual. This is quite sufficient for a simple extension like this.

Finally the three pairs of accessor methods allow each field to be read or set.

The implementation of the SystemC generic payload extension class for JTAG, JtagExtensionSC, may be found in sys-models/jtag-soc/JtagExtensionSC.cpp in the distribution.