Systems and methods for generating an RTL description based on logical signal groupings are described. Logical interfaces are declared in a compressed form, and logical signal grouping is defined in a markup document. The definitions from the markup document are used by expansion scripts to populate RTL modules and encapsulate block connectivity and functionality. Multiple interfaces can be created instantly, and interface definitions for common interfaces may be easily re-defined. Default values may be assigned to module outputs for testing purposes, allowing for multi-module simulations where certain modules are shelled-out.