Register Model Structure

Component Tree

After compilation, the resulting register model is modeled as an object tree.

Consider the following snippet of SystemRDL:

reg my_reg_t {
    field {} f1;
    field {} f2;

addrmap top {
    my_reg_t A[4];
    my_reg_t B;

Once compiled, the resulting component tree is as follows:


The resulting tree has the following characteristics:

  • Each component instance is represented by a Component object.

  • Any instances within a component are referenced as children of the component.

  • The $root meta-component contains an instance of the elaborated top-level addrmap, as well as any signals that were instantiated in the root namespace.

  • All instances and their descendants are unique objects.

  • Arrays of instances are encoded as a single object that stores the array’s dimensions.

  • Each instance in the component tree keeps a reference back to its original “as-defined” non-instance object.

    • For example, instances A and B are both based off of the common component definition my_reg_t (shown in gray).

    • Note that top and $root instances also have similar references, but are not shown in the diagram above.

Node Overlay

The “Node” overlay is an additional data structure that is used to make model traversal unambiguous.

Each Node object provides the following:

  • Reference to its corresponding Component instance.

  • Reference to its immediate parent

  • The current array index of an instance.

  • Helper functions that simplify querying and traversing the register model.

Most of the your interaction with the register model should be through Node objects.

When the you traverse the register model, Node objects are dynamically created in order to provide unambiguous context as to which instance is being represented.

Consider the following lineage of instances from the previous example top -> A -> f1. Note that register “A” is declared as an array of 4 instances.


Since the overlay provides references back up to each node’s parent as well as an array index, the unambiguous lineage can be known. (purple f1 node vs orange f1 node)