Driver and Sequencer handshake mechansim in UVM

Hello everyone. Here in this post we will learn how driver and sequencer communicate with each other in UVM in a simple way.

Driver is a component which is used to provide stimulus for DUT. Sequencer is a component which gets the sequence item from sequence and provide it to driver.

We now will understand how driver communicate with sequencer in simple points.

• Driver class should be derived from uvm_driver base class and should be parameterized with uvm_sequence_item.
• sequencer class should be derived from uvm_sequencer base class which is also parameterized with uvm_sequence_item.
• Sequencer has number of methods defined to get sequence items from sequence level. Below is the list.

1. get_next_item(output REQ req) : This is a virtual task which is a blocking method. Until sequencer gets sequence item from sequence this will be blocked.This must be associated with Item_done.
2. try_next_item(output REQ req): This is a virtual task and same as get_next_item(). It will return immediately and it is non-blocking method. Only successful getting of sequence item must be associated with item_done().
3. get(output REQ req): This is a virtual task which is blocking until sequencer gets sequence item. item_done will be implicitly called. explicit item_done shall not be called.
4. item_done(input RSP rsp=null): It is a function which does not require any argument by default. successful try_next_item or get_next_item must call this method at the end of complete driver action.  
5. put(input RSP rsp) : This is a virtual task which is used to give response to sequence. This will be used along with get method. This will internally call put_response method.
6. peek(output REQ req): This method will be internally called by get_next_item, try_next_item and get method. This is the base for all these methods.

• We are now familiar with the sequencer methods. But now this method should be called in our driver to get the sequence items and to send response back to the sequence.
• This is done with the help of special TLM connection. uvm_driver base class have a handle of uvm_seq_item_pull_port known as "seq_item_port".
• Same way uvm_sequencer base class have a handle of uvm_sequence_item_pull_imp known as "seq_item_export". 
• These port/export is constructed in uvm driver/ uvm_sequencer base class by default.
• In the agent, which instantiates sequencer and driver these TLM's should be connected. (seq_item_port.connect(seq_item_export)).

       
        


       

• Now we will go little in depth to understand how driver can access sequencer's method. 
• below you can see seq_item_pull_port and seq_item_pull_imp class has UVM_SEQ_ITEM_PULL_IMP macros which is common.

      
   

• We will see what that macro defines

        

• All the methods required to access sequence items in driver are defined here.
• So when we call get_next_item from our driver class, the above defined method will be called which will call implementations methods.
• Implementation is the sequencer which has all the required methods.

This way driver and sequencer communicate with each other. One more point is that it is also possible to access all these methods with sequencer handle.

Hope this post helped in understanding uvm_driver communication in easy, better and detailed way. Stay tuned for more posts on UVM...!! we will also have posts from System Verilog.