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Methods Part-I

Saturday, 19 February 2022 16:54 Semicon Editor 01

Introduction to Methods

e methods are similar to C functions, Verilog tasks, functions, and VHDL processes. There are two types of methods in e language.

Regular Method : Execute within a single point of simulation time (within zero time)

Time Consuming Method : Executes over multiple cycles.

TCMs are used to synchronize processes in an e program with processes or events in the DUT. Within a single e program, multiple TCMs can execute ether in sequence or concurrently, along parallel but separate threads. A TCM can also have internal branches, which are multiple action blocks executing concurrently.

Methods defined in one module can later be overwritten, modified or enhanced in subsequent modules using the extend mechanism. This is something that makes e language more powerful compared to VERA or C++ based verification.

Implementing an e method is usually done in e. However, you might want to write a C routine and convert it into an e method. You can do this by declaring an e method that is implemented in C. We can also use Verilog task and function in e.

Defining and Extending Methods

There are two ways to define a method is [ C routine ]
is undefined | empty
There are two ways to extend a method

is also | first | only
You can also use is to extend a method in the following cases:
The method was previously introduced with is undefined or is empty and has not been previously extended in this struct or in any struct that inherits from this struct.
The method was previously introduced (and perhaps extended) in a struct that this struct inherits from, as long as the method has not already been extended in this struct or in any struct that inherits from this struct using like.
We will see all this is detail below.

Is

We define pure e method for first time using is. A TCM is a time-consuming method that is distinguished from a regular method by the presence of @event and can use time-consuming actions such as sync and wait.

Syntax :

method-name ([parameter-list]) [: return-type]@event is {action;...}

Below is simple example which shows how to declare a regular method.

 1 <'

2 extend sys {

3 // This is how delcare a method

4 say_hello() is {

5 out ("Hello World");

6 };

7

8 run() is also {

9 say_hello();

10 };

11 };

12 '>

Here the method is say_hello, and it is regular method, which does not contain wait statements.

is undefined/empty

Declares an abstract regular method or an abstract TCM with no defined functionality. Abstract methods are place holders that you can extend at a later point.

Syntax

method-name ([parameter-list]) [: return-type] [@event-type] is [undefined|empty]

	Parameters
Parameter	Description
method-name	A legal e name
parameter-list	A list composed of zero or more parameter declarations of the form param-name,The parentheses around the parameter list are required even if the parameter list is empty
return-type	For methods that return values, specifies the data type of the return value
@event-type	Specifies a default sampling event that determines the sampling points of the TCM.
undefined	No action block is defined for the method yet; an action block must be defined in a subsequent module before this method is called. A runtime error is issued if it is called before it is defined.
empty	The action block is empty, but no error is issued if it is called. Empty value-returning methods return the default value for the type.
Parameter	Description
method-name	A legal e name
parameter-list	A list composed of zero or more parameter declarations of the form param-name,The parentheses around the parameter list are required even if the parameter list is empty
return-type	For methods that return values, specifies the data type of the return value
@event-type	Specifies a default sampling event that determines the sampling points of the TCM.
undefined	No action block is defined for the method yet; an action block must be defined in a subsequent module before this method is called. A runtime error is issued if it is called before it is defined.
empty	The action block is empty, but no error is issued if it is called. Empty value-returning methods return the default value for the type.

is inline

Defining a method as inline requires Specman Elite to generate code that enables the C compiler to inline the method. The C compiler to place all the code for the method at each point in the code where the method is called. This inline expansion allows the compiler to optimize the inline method code for the best performance. Methods that are frequently called and involve computation are good candidates for inline definition

Syntax

method-name ([parameter-list]) [: return-type] is inline {action;...}

Note:

The Gnu C compiler can inline most methods declared as inline without any additional flags.
A method originally defined as inline cannot be redefined using is only, is first, or is also.
Methods defined in when conditional struct members cannot be inline.
Time-consuming methods (TCMs) cannot be inline.
Example

1 <'