The five JTAG ports in ORPSoC are modeled as SystemC sc_in<bool> (for jtag_tck, jtag_tdi, jtag_tms and jtag_trst) and sc_in<bool> ports (for jtag_tdo).

Rather than drive the JTAG ports directly, requiring detailed management of the Test Access Port (TAP) state machine, the GDB interface uses the Embecosm cycle accurate SystemC JTAG interface [9]. This provides a SystemC FIFO interface on which requests to read and write the JTAG instruction and data registers can be queued, as well as requests to reset the JTAG TAP state machine.