Clock event

The D gate freezes a copy of the variable input at the moment the clock event occurs. 

What if we want to model a flip-flop with synchronous preset and clear In such a case, simply describe the synchronous preset and clear logic within a clocked always statement (an always statement with a clock event). Here is an example. 

A task call can represent either combinational logic or sequential logic depending on the context under which the task call occurs. By this, we mean that the output parameters of a task call may imply memory depending on the context in which they are assigned. For example, if a task call occurs in a clocked always statement (always statement with a clock event), then an output parameter in a task call may be synthesized as a flip-flop this is determined by using the flip-flop inference rales. A synthesis system implements a task call by expanding the task call in-line with the rest of the code in effect, no separate hierarchy for the task call is maintained. 

If a variable is assigned a value z in an always statement in which the variable is also inferred as a flip-flop, then it becomes necessary to save the enabling logic of the three-state also in a flip-flop. Here is the same example as above except that the always statement is controlled by a clock event. 

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). 

Recommendation For an always statement without a clock event (that is, when modeling combinational logic), include all variables read in the always statement in the event list. 

The use of the term process does not imply a heavyweight construct with memory protection, etc. It merely implies an abstract concurrent activity. Each process experiences a potentially infinite number of invocations (each in response to its event-trigger). The event may originate from the clock, the interface, or another process. If the clock event is regular, then the process is termed periodic. 

The process P,- writes scheduling requests Ai on its signals Si to the kernel and reads directly via the kernel clock events and the state E = J E,- of signals ... 

There are two types of prospective memory time based and event based (Kliegel, Martin, McDaniel, and Einstein, 2001 Logie, May lor, Della Sala, and Smith, 2004 Smith, 2003). Time based, also called self cued prospective memory, is when the task has to be executed at a specific arrd fixed time for example going to an appointment at ten o clock. Event based or extenrally cued is the one most relevant to ATC. At the onset of a certain event one must be triggered to execute a specific command in the above example, ATC has to clear a plarre to take-off, therefore ATC mirst take irrto accormt that mrrltiple prospective tasks can occrrr simirltaneously. 

A novel feature of the representation is the first-order predicate calculus that is used to specify complex timing constraints between events. The calculus has all the usual primitives and two new ones based on chronological and causal relationships. Timing constraints consist of three parts quantifiers that specify the events involved in the constraint, a context in which the constraint applies to these events, and requirements on the relative time of occurrence of each event. The context uses the two new primitives. For example, the chronological relationship is used to express constraints between an event and the clock event that immediately follows. The causal relationship is used to specify that a particular constraint holds only if the events were part of one sequence of events and not another, as for example, to specify a hold time requirement during a write operation and not during a read. 

The simplest manifestation of nonlinear kinetics is the clock reaction—a reaction exliibiting an identifiable mduction period , during which the overall reaction rate (the rate of removal of reactants or production of final products) may be practically indistinguishable from zero, followed by a comparatively sharp reaction event during which reactants are converted more or less directly to the final products. A schematic evolution of the reactant, product and intenuediate species concentrations and of the reaction rate is represented in figure A3.14.2. Two typical mechanisms may operate to produce clock behaviour. 

Figure A3.14.2. Characteristic features of a clock reaction, illustrated for the Landolt reaction, showing (a) variation of product concentration witii induction period followed by sharp reaction event (b) variation of overall reaction rate witli course of reaction.

Correlated events are related in time and this time relation can be measured either with respect to an external clock or to the events themselves. Random or uncorrelated events bear no fixed time relation to each other but, on the other... 

Any one bin can be electronically distinguished from the next one, and therefore the bins can be used like the tick of a standard clock. Each bin serves as one tick, which lasts for only 0.3 nsec. By counting the ticks and knowing into which bin the ion pulse has gone, the time taken for the ion to arrive at the detector can be measured to an accuracy of 0.3 nsec, which is the basis for measuring very short ion arrival times after the ions have traveled along the TOE analyzer tube. Each ion arrival pulse (event) is extracted from its time bin and stored in an associated computer memory location. 

A typical transputer architecture. The transputer (sometimes referred to as a computer on a chip) has four input/output links (0, 1, 2, 3) to other transputers, a channel for inputting/requesting data (event link), some built-in random-access memory, an interface to the main operating system (clock, boot, etc.), and an external memory interface. Internal communication is via a bus. 

Real-time clocks (RTCs). Real-time systems are required to respond to events, as they occur, in a timely manner. This is especially crucial in process control systems where control actions applied at the wrong time may amplify process deviations or destabilize the processes. The nodes in the systems are interrupted periodically by the real-time clocks to maintain the ac tual elapsed times. 

All data recorded in the data base have been acquired from plant records. Statistical reductions of data for generation of reports or specific end use are available. Data are currently collected from four operating plants (eight units). Time clocks have been installed on components, to record actual exposure time. Event data are available on a broad variety of safety and commercial grade components including pumps, valves, transformers, diesels, filters, tanks (vessels), and heat exchangers. 

The criteria used to identify events that require expedited reporting to European regulatory authorities are shown in Figure 12.6. The maximum time allowed for the submission of an expedited report is 15 days. The clock starts from the time that any... 

There are apparently customers who soldered on ceramic capacitors in their power supplies and found the clock was just too low. They figured the capacitance was above the guaranteed upper tolerance band (a rare event with commercial ceramics ), and shipped them right back to their manufacturers. But the problem was only that as soon as the PCBs went through the soldering process, age reset (or de-aging) occurred and so capacitance rose. If only they had waited for some more time, their clocks would have been right on However, I would have preferred SMD him capacitors if stability was so important. 

Other chemical changes can be much faster than the RNA conformational changes illustrated here. Photodissociation of sodium iodide (Nal) in the gas phase occurs on the time scale of a few picoseconds (10-12 seconds). To measure this phenomenon, Nal molecules are irradiated by a sub-picosecond ultraviolet pulse of radiation, and the subsequent events are clocked by another short light pulse that detects the newborn... 

TA are used to model and analyze dynamic systems with discrete and timed behavior. One of their strengths is the easy modeling in a decomposed fashion as a set of often small and individually acting automata. Time in TA is modeled in a very natural way by a set of clocks that simply measure the time between events. This is a major difference to MIP techniques, where time and dynamic components are described in a rather artificial way by providing variables and inequalities for every point of time within a discretized time horizon. In addition to the advantages in modeling, TA serve as a computational model which can be analyzed by techniques for reachability analysis. These techniques are widely used in the context of verification, in which the objective is to detect possible undesired (bad or forbidden) behaviors [9-11]. The success of these techniques was pushed by the availability and increasing performance of tools for TA, e.g., Uppaal [9, 10, 12, 13]. 

Special clock variables called docks a, i = 1,..., NC are used to measure the time between events. The values of the clocks increase permanently with the rate t = 1. Clocks are used to measure the durations of tasks for the resource automata, and to measure the waiting between two tasks for place automata. 

Multi-static radar is usually combined with the net-centric approach to data exchange. All sensor sites have to be connected by high-throughput, self-configuring data links. The data links should also provide a very stable clock to make all processing coherent, and very accurate time data to synchronize all events in the distributed system. 

The periodic recurrence of cell division suggests that globally the cell cycle functions like an autonomous oscillator. An extended model incorporating the sequential activation of the various cyclin-dependent kinases, followed by their inactivation, shows that even in the absence of control by cell mass, this sequence of biochemical events can operate as a limit cycle oscillator [145]. This supports the union of the two views of the cell cycle as dominoes and clock [146]. Because of the existence of checkpoints, however, the cell cycle stops at the end of certain phases before engaging in the next one. Thus the cell cycle looks more like an oscillator that slows down and makes occasional stops. A metaphor for such behavior is provided by the movement of the round plate on the table in a Chinese restaurant, which would rotate continuously under the movement imparted by the participants, were it not for frequent stops. 

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