Verification Components User Guide


This library is released as a BETA version. This means non-backwards compatible changes are still likely based on feedback from our users.

Included verification components (VCs):

  • Avalon Memory-Mapped master

  • Avalon Memory-Mapped slave

  • Avalon Streaming sink

  • Avalon Streaming source

  • AXI-Lite master

  • AXI read slave

  • AXI write slave

  • AXI stream master

  • AXI stream monitor

  • AXI stream protocol checker

  • AXI stream slave

  • RAM master

  • Wishbone master

  • Wishbone slave

  • UART master

  • UART slave

In addition to VCs VUnit also has the concept of Verification Component Interfaces (VCI). A single VC typically implements several VCIs. For example an AXI-lite VC or RAM master VC can support the same generic bus master and synchronization VCI while also supporting their own bus specific VCIs.


The main benefit of generic VCIs is to reduce redundancy between VCs and allow the user to write generic code that will work regardless of the specific VC instance used. For example control registers might be defined as a RAM-style bus in a submodule but be mapped to an AXI-lite interface on the top level. The same testbench code for talking to the submodule can be used in both the submodule test bench as well as the top level test bench regardless of the fact that two different VCs have been used. Without generic VCIs copy pasting the code and changing the type of read/write procedure call would be required.

Neither a VC or a VCI there is the memory model which is a model of a memory space such as the DRAM address space in a computer system. The memory mapped slave VCs such as AXI and Wishbone make transactions against the memory model which provides access permissions, expected data settings as well as the actual buffer for reading and writing data.

Verification Component Interfaces

A verification component interface (VCI) is a procedural interface to a VC. A VCI is defined as procedures in a package file. Several VCs can support the same generic VCI to enable code re-use both for the users and the VC-developers.

List of VCIs included in the main repository:

Included verification component interfaces (VCIs):

  • Bus master: generic read and write of bus with address and byte enable.

  • Stream: push and pop of data stream without address.

  • Synchronization: wait for time and events.

Verification Components

A verification component (VC) is an entity that is normally connected to the DUT via a bus signal interface such as AXI-Lite. The main test sequence in the test bench sends messages to the VCs that will then perform the actual bus signal transactions. The benefit of this is both to raise the abstraction level of the test bench as well as making it easy to have parallel activity on several bus interfaces.

A VC typically has an associated package defining procedures for sending to and receiving messages from the VC. Each VC instance is associated with a handle that is created in the test bench and set as a generic on the VC instantiation. The handle is given as an argument to the procedure calls to direct messages to the specific VC instance.