What is a UVM sequence ?
UVM sequences are made up of several data items which can be put together in different ways to create interesting scenarios. They are executed by an assigned sequencer which then sends data items to the driver. Hence, sequences make up the core stimuli of any verification plan.
Steps to create a UVM sequence1. Create a user-defined class inherited from
uvm_sequence, register with factory and call
2. Declare the default sequencer to execute this sequence
// my_sequence is user-given name for this class that has been derived from "uvm_sequence" class my_sequence extends uvm_sequence; // [Recommended] Makes this sequence reusable. Note that we are calling // `uvm_object_utils instead of `uvm_component_utils because sequence is a uvm_transaction object `uvm_object_utils (my_sequence) // This is standard code for all components function new (string name = "my_sequence"); super.new (name); endfunction endclass
3. Define the body method
// [Optional] my_sequencer is a pre-defined custom sequencer before this sequence definition `uvm_declare_p_sequencer (my_sequencer)
// [Recommended] Make this task "virtual" so that child classes can override this task definition virtual task body (); // Stimulus for this sequence comes here endtask
UVM Sequence Example
class my_sequence extends uvm_sequence; `uvm_object_utils (my_sequence) function new (string name = "my_sequence"); super.new (name); endfunction // Called before the body() task task pre_body (); ... endtask task body (); my_data pkt; `uvm_do (pkt); endtask // Called after the body() task task post_body(); ... endtask endclass
Note the following from the example shown above.
- my_sequence is inherited from
- It is registered with the factory using
`uvm_object_utilsbecause it is a transaction item
- The main stimulus is written within the
post_body()are useful callbacks to be used if required
- A data packet is created and sent for execution using
post_body methods are not invoked in a
`uvm_do macro call.
`uvm_do macro will allocate an object of type my_data to pkt, randomize it and send it to the default sequencer associated to execute this sequence. Use of this macro simply reduces the code required to achieve the objectives mentioned before.
Learn how to create and use a sequence