AR# 64050


Vivado Simulator - Using Mixed Language Simulation


The Vivado simulator supports mixed language project files and mixed language simulation.

This allows you to include Verilog modules in a VHDL design, and vice versa.
This article highlights some key points in mixed language simulation using Vivado simulator.


Restrictions on Mixed Language in Simulation
  • A VHDL design can instantiate Verilog/System Verilog (SV) modules and a Verilog/SV design can instantiate VHDL components.
    Component instantiation-based default binding is used for binding a Verilog/SV module to a VHDL component.
    Specifically, configuration specification and direct instantiation are not supported for a Verilog/SV module instantiated inside a VHDL component.
    Any other kind of mixed use of VHDL and Verilog, such as VHDL process calling a Verilog function, is not supported.

  • A subset of VHDL types, generics, and ports are allowed on the boundary to a Verilog/SV module.
    Similarly, a subset of Verilog/SV types, parameters and ports are allowed on the boundary to VHDL components.
    The supported data types can be found in (UG900) Vivado Design Suite User Guide: Logic Simulation.
      Note: Connecting an entire VHDL record object to a Verilog object is unsupported.
      However, VHDL record elements of a supported type can be connected to a compatible Verilog port.

  • A Verilog/SV hierarchical reference cannot refer to a VHDL unit, nor can a VHDL expanded or selected name refer to a Verilog/SV unit.
    However, Verilog/SV units can traverse through an intermediate VHDL instance to go into another Verilog/SV unit using a Verilog hierarchical reference.

Binding and Searching rules
When you instantiate a VHDL component in a Verilog/SV module or a Verilog/SV module in a VHDL architecture, the xelab command does the following:
  • First searches for a unit of the same language as that of the instantiating design unit.
  • If a unit of the same language is not found, xelab searches for a cross-language design unit in the libraries specified by the -L option.
The search order is the same as the order of appearance of libraries on the xelab command line.
Note: When using the Vivado IDE, the library search order is specified automatically.
No user intervention is necessary or possible.

Instantiation of Mixed Language Components
Instantiating a Verilog Module in a VHDL Design Unit:
  1. Declare a VHDL component with the same name and in the same case as the Verilog module that you want to instantiate.
  2. Use named or positional association to instantiate the Verilog module.

Instantiating a VHDL Component in a Verilog/SV Design Unit:
To instantiate a VHDL component in a Verilog/SV design unit, instantiate the VHDL component as if it were a Verilog/SV module.

To ensure that you are correctly matching port types, review the Port Mapping and Supported Port Types tables in (UG900) Vivado Design Suite User Guide: Logic Simulation.

Linked Answer Records

Master Answer Records

Answer Number Answer Title Version Found Version Resolved
58881 Xilinx Simulation Solution Center - Design Assistant - Language Support N/A N/A
AR# 64050
Date 04/08/2015
Status Active
Type General Article
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