3.2.2. The JtagSC SystemC Module Class

3.2.2. The `JtagSC` SystemC Module Class

This SystemC module class provides the primary interface. Users can queue instances of TapAction on its FIFO and it will generate the correct sequence of JTAG tap pin signals.

JtasSC defines a set of signal ports to connect to the target model implementing JTAG

```
sc_core::sc_in<bool>  sysReset
	    
```
Input. The system wide reset signal (active high). Whenever this is active JtagSC will drive the TRST signal to its active state (low).
```
sc_core::sc_in<bool>  tck
	    
```
Input. The JTAG clock signal. This must be synchronous with the TCK signals to connected devices implementing JTAG
```
sc_core::sc_out<bool>  tdi
	    
```
Output. The TDI signal. For JtagSC it is an output, because this class is generating the required signals on TDI from the actions which have been queued.
```
sc_core::sc_in<bool>  tdo
	    
```
Input. The TDO signal. For JtagSC it is an output from which the result of the actions which have been queued is built up
```
sc_core::sc_out<bool>  tms
	    
```
Output. The TMS signal. For JtagSC it is an output, because this class is generating the required signals to drive the TAP state machine from the actions which have been queued.
```
sc_core::sc_out<bool>  trst
	    
```
Output. The TRST signal. Driven low (active) whenever the system reset (sysReset) is active (high). For JtagSC it is an output, because this class generates the reset when required.
Users connecting to modules which do not implement TRST should tie this off to a dummy signal

JtasSC defines a FIFO on which users queue JTAG actions.

```
sc_core::sc_fifo<TapAction *> *tapActionQueue
	    
```
The JTAG actions are of type TapAction and its subclasses. Over successive TCK cycles, the JtagSC will generate the required TMS and TDI signals and capture the TDO signals. When complete the SystemC sc_event from the action's creation is signaled.

The public methods of JtagSC are:

```
JtagSC (sc_core::sc_module_name  name,
        int                      fifo_size = DEFAULT_TAP_FIFO_SIZE)
	    
```
The constructor of new JTAG modules. The first argument, name, like all SystemC modules, is the name of the module. The optional second argument specifies the size of FIFO on which actions may be queued. Its default value, DEFAULT_TAP_FIFO_SIZE is 256 in the current implementation.
```
~JtagSC ()
	    
```
The destructor for JTAG modules. This deletes the FIFO and a number of internal data structures.