ralgen: A FuseSoC generator for UVM RAL package

The ralgen.py script is implemented as a FuseSoC generator. which enables the automatic creation of the SystemVerilog UVM RAL package and its insertion into the dependency tree when compiling the DV testbench.

This approach is useful for DV simulation flows that use FuseSoC as the backend to generate the filelist for compilation. A separate RAL package generation step is no longer needed since it gets handled within FuseSoC.


The adjoining ralgen.core file registers the ralgen generator. The FuseSoC core file that ‘calls’ the generator adds it as a dependency. When calling the generator, the following parameters are set:

  • name (mandatory): Name of the RAL package (typically, same is the IP).
  • dv_base_prefix (optional): The prefix added to the base classes from which the register classes are derived. Set this option to derive the register classes not from the default dv_base_reg, but from user defined custom class definitions.
  • ip_hjson: Path to the hjson specification written for an IP which includes the register descriptions. This needs to be a valid input for reggen.
  • top_hjson: Path to the hjson specification for a top level design. This needs to be a valid input for topgen.

Only one of the last two arguments is mandatory. If both are set, or if neither of them are, then the tool throws an error and exits.

The following snippet shows how it is called:

    generator: ralgen
      name: <name>
      ip_hjson|top_hjson: <path-to-hjson-spec>
      [dv_base_prefix: my_base]

      - ral

Note that the path to hjson specification in the snippet above is relative to the core file in which the generator is called.

ralgen script

When FuseSoC processes the dependency list and encounters a generator, it passes a YAML file containing the above parameters to the generator tool (the ralgen.py) as a single input. It then parses the YAML input to extract those parameters.

ralgen.py really is just a wrapper around reggen and the util/topgen.py scripts, which are the ones that actually create the RAL package. Due to the way those scripts are implemented, RAL packages for the IP level testbenches are generated using reggen, and for the chip level testbench, util/topgen.py. Which one to choose is decided by whether the ip_hjson or top_hjson parameter is supplied.

In addition, the ralgen.py script also creates a FuseSoC core file. It uses the name parameter to derive the VLNV name for the generated core file.

The generated core file adds lowrisc:dv:dv_base_reg as a dependency for the generated RAL package. This is required because our DV register block, register and field models are derived from the DV library of classes. This ensures the right compilation order is maintained. If the dv_base_prefix argument is set, then it adds lowrisc:dv:my_base_reg as an extra dependency, where my_base is the value of the argument as shown in the example above. This core file and the associated sources are assumed to be available in the provided FuseSoC search paths.


The script is not designed to be manually invoked, but in theory, it can be, if a YAML file that contains the right set of parameters is presented to it (compliant with FuseSoC).

If the user wishes to create the RAL package manually outside of the DV simulation flow, then the make command can be invoked in the hw/' area instead. It generates the RTL, DV and SW collaterals for all IPs, as well as the top level in a single step.