How to Get the Response ID in UVM_Sequence
The UVM_Sequence is a powerful mechanism in Universal Verification Methodology (UVM) for generating and driving test sequences. During the test, a sequence may need to track the response ID of a transaction to ensure proper correlation and verification. This article will delve into the process of retrieving response ID within a UVM_Sequence.
Understanding the UVM_Sequence and Response ID
The UVM_Sequence is responsible for orchestrating the order and content of transactions that are sent to the DUT. The response ID acts as a unique identifier associated with each transaction sent by the sequence. This allows the sequence to track the responses it expects and correlate them to the transactions it sent.
Retrieving Response ID within a UVM_Sequence
There are two primary approaches to get the response ID within a UVM_Sequence:
1. Utilizing the get_response_id Method
The get_response_id method is a standard function provided within the UVM_Sequence class. This method returns the response ID associated with the current transaction.
class my_sequence extends uvm_sequence #(my_transaction);
...
task body();
my_transaction trans;
...
// Create a transaction
trans = my_transaction::type_id::create("my_trans");
...
// Send the transaction and get the response ID
start_item(trans);
int response_id = get_response_id();
...
endtask
endclass
2. Accessing the response_id Field within the Transaction
The response_id field is a built-in member variable of the UVM_Transaction class. This field is populated by the environment when the transaction is received by the driver or monitor.
class my_transaction extends uvm_transaction;
...
int response_id; // Default declaration in UVM_Transaction
...
endclass
class my_sequence extends uvm_sequence #(my_transaction);
...
task body();
my_transaction trans;
...
// Create a transaction
trans = my_transaction::type_id::create("my_trans");
...
// Send the transaction
start_item(trans);
wait (trans.response_id != 0); // Wait for the response ID to be set
...
endtask
endclass
Considerations for Using Response ID
- Correct Association: Ensure that the response ID retrieved corresponds precisely to the transaction that was sent. This is crucial for accurate correlation and verification.
- Timing: If the response ID is needed within the sequence itself, consider using appropriate wait statements to guarantee that the response ID is available before its use.
Example: Verifying a Simple Bus Interface
// Transaction class
class my_transaction extends uvm_transaction;
rand int data;
int response_id;
...
endclass
// Sequence class
class my_sequence extends uvm_sequence #(my_transaction);
...
task body();
my_transaction trans;
...
// Create and send transaction
trans = my_transaction::type_id::create("my_trans");
trans.data = 10;
start_item(trans);
// Get the response ID
wait (trans.response_id != 0);
int received_response_id = trans.response_id;
...
// Verify that the response ID matches expectation
if (received_response_id == 0) begin
`uvm_error("SEQ_ERROR", "Response ID not received");
end else begin
`uvm_info("SEQ_INFO", "Response ID received successfully: %0d", received_response_id);
end
...
endtask
endclass
// Driver class
class my_driver extends uvm_driver #(my_transaction);
...
function void write(my_transaction trans);
// Send transaction on the bus
...
// Set the response ID
trans.response_id = get_response_id(); // UVM_Driver method
...
endfunction
endclass
In this example, the sequence sends a transaction with data "10" to the bus via the driver. The driver sets the response ID within the transaction before sending it to the DUT. The sequence then retrieves the response ID from the transaction and performs verification.
Conclusion
Retrieving the response ID within a UVM_Sequence is essential for accurate correlation and verification of transactions. Using the get_response_id method or accessing the response_id field within the transaction provides reliable ways to obtain this crucial identifier. Remember to pay attention to timing and association when utilizing response IDs to ensure the integrity of your verification environment.