The Or1ksim ISS library is extended to provide API calls to handle JTAG registers being shifted in and out. The API call, or1ksim_jtag_reset, causes the JTAG unit to process through a reset sequence. The API calls, or1ksim_jtag_shift_ir and or1ksim_jtag_shift_dr, take a byte vector and bit length as arguments and shift specified number of bits through the instruction register and data register respectively.

All three API calls return the time taken by the function in seconds (as a C++ double). A key aspect of this API is that the calls may not be used during the execution of or1ksim_run. This could occur during processing of an upcall, but at such a time the processor is mid-instruction and the state for debug unit processing is inconsistent. This requirement is enforced in the wrapper by use of a SystemC sc_mutex.

The Or1ksim wrapper, Or1ksimIntrSC is further extended by a new derived class, Or1ksimJtagSC, which provides a TLM 2.0 target port to for JTAG transactions and a handler method, jtagHandler, for those requests.

The JTAG target port makes use of TLM 2.0 generic payload with an ignorable extension, used to specify precisely the JTAG operation required and the size in bits of the JTAG register. The class JtagExtensionSC (see Section 11.2) is defined for this purpose.