State machine

In a Moore finite state machine, the output of the circuit is dependent only on the state of the machine and not on its inputs. This is described i pictorially in Figure 3-5. Since the outputs are dependent only on the j state, a good way to describe a Moore machine is to use an always state- j ment with a case statement. The case statement is used to switch between j the various states and the output logic for each state is described in the appropriate branch. The always statement can have the clock event in its] event list to indicate that it is a clocked always statement. This models the] condition of a finite state machine going from state to state synchronously j on every clock edge. The machine state itself is modeled using a reg vari-] able (a variable of reg data type). 

Here is an example of a Moore finite state machine. A reg variable] MooreState is used to model the machine state which can have either of] the four states. The event list indicates that the state transitions occur synchronously on every rising clock edge. 

When this model is synthesized, three flip-flops are inferred two to hold the value of the machine state (MooreState) and one for the output Z. States are encoded using sequential state assignment. 

In a Mealy finite state machine, the output is dependent both on the machine state as well as on the inputs to the finite state machine. This is shown pictorially in Figure 3-8. Notice that in this case, outputs can change asynchronously with respect to clock. 

Here is an example of a Mealy finite state machine. Variable MealyState holds the machine state, while NextState is used to pass information from the combinational logic always statement to the sequential logic always statement. Input Reset asynchronously resets the state to STO. 

There are many ways to model the machine states of a finite state machine. Described here are some of the most common ones. The... 

In this case, the number of bits required for state encoding is dictated by the number of bits in the parameter which in this example is 3 bits. Of course, the machine state MooreState must be made wide enough to hold the new size of three bits. 

Toenshoff H K, Karpuschewsky B, Borbe C (1998) Hard machining state of research. In Proceedings of CIRP/ VDI conference on international high performance tools, VDI Berichte, Ausgabe 1399. Duesseldorf, pp 253-277... 

The states of the model are defined by the member attributes of the class that is instantiated. Then, state faults can be introduced corrupting the values of these attributes. For this case, FIK is introduced in the machine state that rules the model behaviour. 

FIGURE 1.S4 Partition table construction process (a) sample machine state table, (b) first partition step, (c) second partition step, (d) third partition step, (e) composite partition table, (f) reduced state assignments, (g) reduced state table. 

FIGURE 8 Steps in MOVE FOO.L, D3 instruction cycle in which conventional machine states are changed. 

Machine state labels Action to be taken if the head reads Action to be taken if the head reads ... 

The data path modules are specified abstractly. For instance, an arithmetic-logic unit (ALU) would have its width and functions (e.g. add, subtract, and OR) specified. As illustrated in Figure 1-1, the controller is described textually as an abstract state machine (states, next states, and data path elements to enable). The controller is not any more detailed since the actual implementations of the data path... 

FIGURE 7.6 State-space TAFEI diagram that integrates the machine state with the tasks that take the system from state to state. Those tasks can he performed by humans or machines. (From Stanton, N.A. et al., Human Factors Methods, Ashgate, Withston, VT, 2005. With permission.)... 

FIGURE 7.6 State-space TAFEI diagram that integrates the machine state with the tasks that take the system from state to state. . 180... 

Fig. 2. Short x86 assembler snippet (left) adding up the contents of an array AU memory reads in the dynamic execution (right) share a similar machine state, and FI wlU lead to similar results in all cases (a wrong sum). For simplicity registers carry dummy 16-bit values.

These two criteria-wiajcimttm accuracy and minimal number of fault-similarity classes - are contradictory and can be traded for each other. One extremal point (in favor of accuracy) uses the identity function as the state-vector projection - hence defines all available machine state as relevant for grouping - and combines no def/use partition with another it produces fault-similarity classes with one def/use member each, hence conducts an FI experiment for every def/use class, and achieves maximum accuracy. The other extremal point combines all def/use classes to a single similarity class and only conducts a single experiment, resulting in minimal experimentation effort and maximal result error. Between these extremal points exists a large search space with all possible machine-state vector projections, some of them representing Pareto-optimal solutions that optimally trade experiment effort for accuracy. 

We implemented a tool set for the outlined fault-space pruning approach in the Fail [12] FI experimentation framework, configured to run with the Bochs x86 simulator [24]. Ideally, we would simulate faults in a detailed register transfer and gate-level processor model however, since simulation of realistic benchmarks on low-level models is extremely slow, this work chooses a fast architecture simulator. We extended the tracing plugin of Fail with the capability to record the additional machine state listed in Tab. 1 alongside the usual instruction and memory-access trace. 

Fig. 3a shows the training results and fitness values for eCos/baseline after 3 40" of optimization (on a 32-core Intel Xeon E5-4650) Each point represents an individual (the machine-state projection vector, cf. Sect. 3.2), which partitions the training set into... 

As an example, one could solve the halting problem on fixed-size memories using a counter (Gurari, 1989). Since the number of possible machine states is 2 , then if machine states are counted,... 

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