SystemVerilog Structure
A structure can contain elements of different data types which can be referenced as a whole or individually by their names. This is quite different from arrays where the elements are of the same data-type.
Unpacked Structures
A structure is unpacked by default and can be defined using the struct keyword and a list of member declarations can be provided within the curly brackets followed by the name of the structure.
Structure Example
What is the need to typedef a structure .
Only one variable was created in the example above, but if there's a need to create multiple structure variables with the same constituents, it'll be better to create a user defined data type of the structure by typedef . Then st_fruit will become a data-type which can then be used to create variables of that type.
Packed Structures
A packed structure is a mechanism for subdividing a vector into fields that can be accessed as members and are packed together in memory without gaps. The first member in the structure is the most significant and subsequent members follow in decreasing order of significance.
A structure is declared packed using the packed keyword which by default is unsigned.
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Verilog Assignment Patterns
Sigasi Studio has several checks on Verilog assignment patterns.
Default member must be last
Concrete assignments must precede more general assignments. Otherwise, some of those assignments might be ignored (rule 28). In particular:
- for arrays, default must be at the end of the list
- for structures, default must be at the end, but type-default must be after the particular member assignments
Only one default member expression is allowed
Sigasi Studio flags an error when expressions have multiple default assignments (rule 29). In particular:
- arrays cannot have multiple default assignments
- structures cannot have multiple default assignments or multiple type-default assignments
Overwritten type key in assignment pattern
Sigasi Studio warns about duplicate type member keys in assignment patterns (rule 30). This is not an error according to the language reference manual, but the last used type key overwrites previously matched members, making the code confusing and hard to maintain.
Duplicate member key in structure assignment pattern
Sigasi Studio flags an error for duplicate members/index keys in assignment patterns (rule 31). Each member/index key can occur only once.
Mixed named and ordered notation in assignment pattern
Sigasi Studio flags an error when an assignment contains a mix of ordered and named elements (rule 32).
Rule configuration
These rules can be disabled for your project, or their severity and parameters can be modified in the project linting settings . Alternatively, they can be manually configured with the following template:
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SystemVerilog Structure. A structure can contain elements of different data types which can be referenced as a whole or individually by their names. This is quite different from arrays where the elements are of the same data-type. // Normal arrays -> a collection of variables of same data type. int array [10]; // all elements are of int type.
In reply to rr2007: Unpacked or untagged unions have little use in SystemVerilog. You cannot use an assignment pattern with a union; only array’s and struct’s. Hi, how to pass values to the struct fields inside another struct within single line? typedef struct { int unsigned test1; int unsigned test2; int unsigned test3; } type_set1 ...
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