Characterizing and Comparing Direct-Tcl and Indirect-Abstract Approaches for Hardware Build Systems

Build systems become an indispensable part of the software implementation and deployment process. New programming languages are released with the build system integrated into the language tools, for example, Go, Rust, or Zig. However, in the hardware description domain, no official build systems have been released with the predominant Hardware Description Languages (HDL) such as VHDL or SystemVerilog. Moreover, hardware design projects are often multilingual. This paper characterizes and compares two common approaches for hardware build system implementations. The first one is the direct-Tcl approach, in which the build system code is executed directly by the EDA tool during the design build flow. The second one is the indirect-abstract approach, in which the build system produces a Tcl script, which is later run by a proper EDA tool. As none of the existing direct-Tcl build systems were close to the indirect-abstract build systems in terms of supported functionalities, this paper also presents a new direct-Tcl hardware build system called HBS. The implemented build system was used as a representative of direct-Tcl build systems in comparison with indirect-abstract build systems. The main goals of the system include simplicity, readability, a minimal number of dependencies, ease of integration with the existing EDA tools, and independence from version control systems. The system provides a broad design automation, including support for multiple synthesis EDA tools, listing automatically detected cores and targets, automatic testbench targets detection, parallel testbench running, and dependency graph generation.