Explicit versus implicit state models in Software Development Code 3 of 9 in Software Explicit versus implicit state models

How to generate, print barcode using .NET, Java sdk library control with example project source code free download:
Explicit versus implicit state models use software code39 printing toembed bar code 39 in software QR Code Standardiztion These two Software barcode code39 classes are easily told apart by counting the wait statements per process statement. In an explicit state model, there is no process statement with more than one wait on or wait until; process statements with a sensitivity list (and hence no wait) are more typical, however. In either case, program execution always returns to the same line of code and suspends there after having completed one full turn.

One or more VHDL signals or variables serve to preserve the current state from one process activation to the next. Explicit state models come most naturally to. 4.3 PUTTING VHDL TO SERVICE FOR HARDWARE SYNTHESIS combinatio Software Code 3 of 9 nal operations output function g next state function f o(k) oup o(k) = g( i(k),s(k) ) = s(k) s(k+1) = f( i(k),s(k) ) = ...


s(k+1) next state state register dis by3 00 by4 01 by4 by3 by4 by3 11 dis by4 10 oup := "00" b) dis c) by3 dis output := "00" forever wait on event on clock repeat until clock is high and counting is enabled oup := "01" wait on event on clock s(k) present state a) repeat until clock is high and counting is enabled oup := "10" wait on event on clock repeat until clock is high and counting is enabled 3 divide by 4 oup := "11" wait on event on clock repeat until clock is high and counting is enabled .. i(k) cntrl Fig. 4.18 Software 39 barcode Three formalisms that a ect the writing of software models for sequential behavior.

Data dependency graph (a), state chart (b), Nassi Shneiderman diagram (c). Note that the programmable divide-by-3/divide-by-4 counter chosen for illustration is a Medvedev machine..

hardware d esigners who are accustomed to thinking in terms of nite state machines (FSMs) along with visual formalisms such as schematics, state graphs, and the like. An implicit state model, in contrast, is immediately recognized by the presence of multiple waits in process statements. Upon activation, the simulator executes instructions until the next wait statement encountered causes it to suspend.

Suspension may thus occur at distinct lines of code, and each wait statement represents a speci c state of the model. There is no tangible state variable. Rather, it is the return address to the suspended process that assumes this role during simulation, hence the name implicit state.

Implicit state models resemble the way how software designers code algorithms, and are related to Nassi Shneiderman diagrams, aka structograms, and owcharts. See g.4.

18 and table 4.4 for a comparison. Implicit state models occasionally nd applications in the context of purely behavioral simulation, that is above the RTL level in the abstraction hierarchy.

They must be translated into an explicit state model at the RTL level before synthesis can begin. Code examples in this text refer to explicit state models exclusively..

How to capture a finite state machine in VHDL The restri ction to explicit state models notwithstanding, one still has the choice of putting an FSM into one VHDL process statement or of distributing it over two or more concurrent processes.. Architectures of VLSI Circuits Table 4.4 Explicit and implicit state models compared. modelling Software Code-39 style inspired by synchronization mechanism state variable states captured by state transitions captured by output function captured by immediate hardware equivalent synchronous synthesizable explicit state computed state enumerated state data dependency graph state chart, state or schematic diagram graph, or state table sensitivity list or single wait statement (semantically equivalent) declared explicitly as signal or variable and thus of user-de ned type (sub)range of integer range of or of bit vector type enumerated type arithmetic and/or one-to-one translation logic operations from state table arithmetic and/or one-to-one translation logic operations from state table yes yes yes implicit state Nassi Shneiderman diagram multiple wait statements hidden in pointer to current statement multiple wait statements control ow assignment statements depending on wait conditions idem no. Packing an entire FSM into a single process statement The code is organized as illustrated by g.4.19a through c for Mealy, Moore, and Medvedev automata respectively.

44 Evaluation begins with the asynchronous reset and clock inputs to nd out whether the machine s state must be updated. The remaining inputs are processed further down in the process statement. The state must be stored as a VHDL variable because any state change must become visible to the output function within the same process activation.

The process statement must be made sensitive to events on clock and reset and, in the case of a Mealy machine, to events on other input signals as well. Although this coding style is legal VHDL and perfectly acceptable for simulation, its general adoption is discouraged because it is not supported by many synthesis tools and because it may result in ine cient gate-level networks. Distributing an FSM over two (or more) concurrent processes As depicted in g.

4.19d through f, a memorizing process is essentially in charge of maintaining the current state from one activation to the next. A second process statement of memoryless nature computes the next state and the present output value.

This combinational part might just as well be implemented using concurrent/selected/conditional signal assignments. Both present state and next state are being modelled as VHDL signals that go back and forth between the two (or more) processes involved..

The three Software Code 39 Extended classes of autom ata essentially di er in the nature of their output functions. Please refer to sections B.1 and B.

2 if you have doubts ab out the characteristics and equivalence relations am ong those classes..
Copyright © . All rights reserved.