Multi-file Compilation

The ability to split a SystemRDL register model into several RDL files seems like an inherently useful way to manage a design that spans multiple components.

Unfortunately, the SystemRDL 2.0 spec provides no insight on how “compilation units” are handled. Below are the assumptions I made to guide the implementation of this compiler.

Each file is its own compilation unit

  • The contents of files included using one or more include directives become part of the compilation unit of the file within which they are included.

  • Declarations must be completed within the boundaries of a compilation unit. If there is a declaration that is incomplete at the end of a compilation unit, it shall be a compile error.

  • Any Verilog-style preprocessor macros defined within a file are discarded at the end of the compilation unit.


Isolating each file provided to the compiler to a design unit reduces confusing scenarios where things like preprocessor macros ‘leak’ unexpectedly between files.

Namespaces are global across compilation units

The root scope of the official SystemRDL namespaces are shared across files.

Specifically the three namespaces described in the SystemRDL 2.0 spec:

  • Type namespace

    Component definitions, enum types, and struct types

  • Element namespace

    In the $root scope, this is limited to signal instances.

  • Property namespace

    User-defined properties declared in the root scope


If supporting multiple file compile, then sharing these namespaces is essential.

Default property assignments are limited to the compilation unit

Any default property assignments made in the root scope are limited to the current compilation unit. Default property assignments are discarded from the root scope at the end of each compilation unit.


Allowing default property assignments to carry over between files/compilation units would be incredibly confusing. A default property assignment in a prior design unit’s root scope would inevitably influence all subsequent files, causing all kinds of unintended consequences.