Signed Fields

Signed Fields#

SystemRDL does not natively provide a way to mark fields as signed or unsigned. The is_signed user-defined property fills this need.

For this Rust exporter, marking a field as signed changes the primitive integer type of the field to a signed integer (for example, i16 instead of u16). The getter method for the field returns a signed value, sign-extended to size of the primitive type. The setter method takes a signed integer and truncates any unused upper bits.

Properties#

A field can be marked as signed using the following user-defined property:

property is_signed {
    type = boolean;
    component = field;
    default = true;
};

This UDP definition, along with others supported by PeakRDL-regblock, can be enabled by compiling the following file along with your design: udps.rdl.

is_signed

  • Assigned value is a boolean.

  • If true, the field’s getter and setter methods will return/accept a signed Rust integer primitive.

  • If false, the field’s getter and setter methods will return/accept an unsigned Rust integer primitive.

  • If not assigned, the field’s getter and setter methods will return the appropriate type (bool, enum, or unsigned integer). In this case the field value is not considered numeric.

Other Rules#

  • is_signed=true is mutually exclusive with the counter property.

  • is_signed=true is mutually exclusive with the encode property.

Examples#

Below are some examples of fields with different signedness.

Signed Fields#

field {
    sw=rw; hw=r;
    is_signed;
} signed_num[63:0] = 0;

field {
    sw=r; hw=w;
    is_signed = true;
} another_signed_num[19:0] = 20'hFFFFF; // -1

SystemRDL’s own integer type is always unsigned. In order to specify a negative reset value, the two’s complement value must be used as shown in the second example above.

Unsigned Fields#

field {
    sw=rw; hw=r;
    is_signed = false;
} unsigned_num[63:0] = 0;
Contents