lock DLCb, dispatch was not in a state where it could input (or save) the signal. G. In the Validator, select Commands > Toggle MSC Trace: the MSC trace shows the simula- tion executed by the Validator. 6.2.1.2 Analyze the error To understand the bug, you will search in which state process dispatch (in block DLCb) was when process DLC transmitted to it the signal DLCstopped. A. In the Validator, select View > Command Window: as shown in Figure 6.2, the state of each process instance is displayed. You see that process dispatch in block DLCb is in state waitParmResp. Random Simulation 169 ValUI Command File Command List-Process - Command State <<Block DLCa>> dispatch:1 ready <<Block DLCb>> dispatch: 1 aitParmResp AtoB:1 1 ready BtoA: 1 ready Print-Trace 1 Command Figure 6.2 Process states in the Command window B. In the Organizer, double-click on process dispatch: in the page part1, you see that in state waitParmResp, the only input is L_SetParmResp; therefore, when a V76frame is first in the process queue, it is discarded. The error is also easy to understand by looking at the MSC trace. We will not correct this bug, because we will learn how to find it with exhaustive simulation. 6.2.2 Multiple random simulations The random simulation algorithm used in the Validator is based on a pseudorandom number called seed. The initial default seed value, 1, can be changed using Define-Random-Seed. At each random simulation step, the Validator executes a transition selected among the firable transitions according to a random number. For example, if there are two firable transitions, depending on the random number, the first or the second transition is executed. In the previous section, we have used the textual command Random-Down, which performs a single-shot random simulation. To simulate different scenarios in order to hit more errors, you could repeat this simulation several times by returning to the model's initial state (button Top) and entering again the command Random-Down. To simplify your work, the Validator command