scalar.md

Scalars are the most simple definition of a type as they describe a single dimensioned bitvector. They are declared using the Scalar type and can be declared within packages or structs.

Example

The Packtype definition can either use a Python dataclass style or the Packtype custom grammar:

=== "Python (.py)"

```python linenums="1"
import packtype
from packtype import Constant, Scalar

@packtype.package()
class ThePackage:
    # Constants
    TYPE_A_W : Constant = 29
    TYPE_B_W : Constant = 13

    # Typedefs
    TypeA : Scalar[TYPE_A_W]
    TypeB : Scalar[TYPE_B_W]
    TypeC : Scalar[7]
```

=== "Packtype (.pt)"

```sv linenums="1"
package the_package {
    // Constants
    TYPE_A_W : constant = 29
    TYPE_B_W : constant = 13

    // Typedefs
    TypeA : Scalar[TYPE_A_W]
        "Comments can be attached to scalar types"
    TypeB : Scalar[TYPE_B_W]
        "They can be queried from the digested result"
    TypeC : Scalar[7]
        """
        Multiline comments can be used for long descriptions.
        Use triple quotes for these like with Python docstrings.
        """
}
```

As rendered to SystemVerilog:

package the_package;

localparam TYPE_A_W = 29;
localparam TYPE_B_W = 13;

typedef logic [28:0] type_a_t;
typedef logic [12:0] type_b_t;
typedef logic [6:0] type_c_t;

endpackage : the_package

!!! note

Packtype currently processes the width of the scalar at the point of definition,
hence when rendered it does not visibly refer to `TYPE_A_W` but it is internally
consistent with the definition.

Syntax

Scalars must be defined with an explicit bit width expressed within the square brackets ([...]) following the Scalar keyword. The width must be a positive integer value, and may be either hardcoded or refer to a constant or an expression. A second optional boolean parameter may be provided that encodes whether the scalar is signed (True) or unsigned (False), defaulting to unsigned.

@packtype.package()
class ThePackage:
    # Format: <NAME> : Scalar[<WIDTH>, <SIGNED>]
    MyType : Scalar[123, False]

Helper Properties and Methods

Scalar definitions expose a collection of helper functions for properties related to the type:

• <Scalar>._pt_width - property that returns the bit width of the type;
• <Scalar>._pt_signed - property that returns whether the scalar expresses a signed or unsigned type;
• <Scalar>._pt_mask - property that returns a bit mask matched to the width of the type (i.e. (1 << MyScalar._pt_width) - 1).