Introduction to Events

The e language provides temporal constructs for specifying and verifying behavior over time. All e temporal language features depend on the occurrence of events, which are used to synchronize activity with a simulator and within the e program.

• If a path is provided, use the event defined in the struct instance pointed to by the path.
• If no path is provided, the event is resolved at compile time. The current struct instance is searched.
• If the event instance is not found, a compile-time error shall be issued.
  An event named "clk" is defined to be the rising edge of a signal named "top.clk" at another event named "sim". The @ symbol is used with an event name, @event, to mean "when the event is true". The special @sim syntax means at a callback from the simulator. The rise() expression always causes a callback when the signal rises. Therefore, this event definition means "a rise of top.clk causes clk to occur". Occurrences of the "clk" event are represented by arrows.
• 

Defining and Emitting Named Events
Events are defined as a part of a struct definition. When a struct is instantiated, each instance has its own event instances. Each event instance has its own schedule of occurrences. There is no relation between occurrences of event instances of the same type. All references to events are to event instances. The scoping rules for events are similar to other struct members, such as fields.

Events can be attached to temporal expressions, using the option is [only] temporal-expression syntax, or they can be unattached. An attached event is emitted automatically during any tick in which the temporal expression attached to it succeeds.

You can use the emit action in any method to cause an event to occur, whether it has an attached temporal expression or not. The simplest usage of emit is to synchronize two TCMs, where one TCM waits for the named event and the other TCM emits it. Emitting an event causes the immediate evaluation of all temporal expressions that contain that event.
Example - Defining and Emitting Named Events

  1 <'

  2 struct eventEmit {

  3   event clk is rise('top.clk') @sim;;

  4   event nclk is fall('top.clk') @sim;

  5   event startSim;

  6

  7   mainInit()@clk is {

  8    // Do something here

  9    wait [1] *cycle;

 10    // Emit event

 11    emit startSim;

 12    // Do something here

 13   };

 14 };

 15 '>

Sampling Events Overview

Events are used to define the points at which temporal expressions and TCMs are sampled. An event attached to a temporal expression becomes the sampling event for the temporal expression. The event is attached using the @sampling-event syntax:
temporal-expression @sampling-event
The temporal expression is evaluated at every occurrence of the sampling event. The sampling period is the time from after one sampling event up to and including the next sampling event. All event occurrences within the same sampling period are considered simultaneous. Multiple occurrences of a particular event within one sampling period are considered to be one occurrence of that event.

Predefined Events Overview

Predefined events are events which are already defined in e language, they get emitted at pre defined point of time.

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