3.4.2. TapAction

3.4.2. `TapAction`

This is the abstract base class of all the TAP action classes. It provides the common interface, expected by JtagSC.

JtagSC is declared a friend class and the pure virtual process method is made protected. This method can therefore be called by JtagSC, but not by other users of the class. Subclasses of TapAction are expected to implement this method.

Although there are no public instance variables which form part of the API, TapAction maintains some private state.

```
sc_core::sc_event *doneEvent
	    
```
The SystemC event which will be notified when an action completes.
```
int  resetCounter
	    
```
A counter for use when resetting the TAP state machine of the target through checkResetDone (see below).

In addition to the pure virtual process method, TapAction provides the function checkResetDone (see below) as a utility for its subclasses.

`checkResetDone`

The TapActionIRScan and TapActionDRScan subclasses rely on the TAP state machine in JtagSC being an accurate reflection of the TAP state machine in the target. This can only be the case if both have been through a synchronous reset cycle (5 or more TMS=1 cycles).

The TRST signal cannot be used as a guide, since it is an optional signal, which may not be implemented by targets.

Instead the TAP state machine class, TapStateMachine records whether it has been through a reset cycle. It relies on other classes to use (and set) this information as is helpful.

Both TapActionIRScan and TapActionDRScan check this information, and if necessary force the state machine through a reset to synchronize with the model.

This method is a utility to provide that function for subclasses. A subtlety of its implementation is that it sets the value of the TAP state machine flag as soon as it has provided the final (fifth) TMS signal, but does not return true to indicate no reset is needed until its subsequent call. This allows users to distinguish whether they are about to complete reset, or have already completed it in the previous TCK cycle. This in turn allows the method to provide the functionality for TapActionReset.