UVM Verification Methodology

UVM testbench design patterns and best practices for the AXIUART_RV32I verification environment.

When to Use This Skill

• Creating UVM testbench components (tests, environments, agents)
• Implementing drivers, monitors, sequences, or scoreboards
• Debugging UVM configuration or communication issues
• Resolving UVM naming convention questions
• Setting up factory patterns or objection management

UVM Component Naming

Component Hierarchy

File Naming

UVM Component Templates

Driver Template

class uart_driver extends uvm_driver #(uart_transaction);
    `uvm_component_utils(uart_driver)
    
    virtual uart_if vif;
    
    function new(string name = "uart_driver", uvm_component parent = null);
        super.new(name, parent);
    endfunction
    
    virtual function void build_phase(uvm_phase phase);
        super.build_phase(phase);
        if (!uvm_config_db#(virtual uart_if)::get(this, "", "vif", vif)) begin
            `uvm_fatal(get_type_name(), "Virtual interface not found in config DB")
        endif
    endfunction
    
    virtual task run_phase(uvm_phase phase);
        forever begin
            seq_item_port.get_next_item(req);
            drive_transaction(req);
            seq_item_port.item_done();
        end
    endtask
    
    virtual task drive_transaction(uart_transaction trans);
        // Implementation
        `uvm_info(get_type_name(), 
            $sformatf("Driving transaction: %s", trans.convert2string()), 
            UVM_HIGH)
    endtask
endclass

Monitor Template

class uart_monitor extends uvm_monitor;
    `uvm_component_utils(uart_monitor)
    
    virtual uart_if vif;
    uvm_analysis_port #(uart_transaction) analysis_port;
    
    function new(string name = "uart_monitor", uvm_component parent = null);
        super.new(name, parent);
    endfunction
    
    virtual function void build_phase(uvm_phase phase);
        super.build_phase(phase);
        if (!uvm_config_db#(virtual uart_if)::get(this, "", "vif", vif)) begin
            `uvm_fatal(get_type_name(), "Virtual interface not found in config DB")
        endif
        analysis_port = new("analysis_port", this);
    endfunction
    
    virtual task run_phase(uvm_phase phase);
        uart_transaction trans;
        forever begin
            trans = uart_transaction::type_id::create("trans");
            collect_transaction(trans);
            `uvm_info(get_type_name(), 
                $sformatf("Collected: %s", trans.convert2string()), 
                UVM_HIGH)
            analysis_port.write(trans);
        end
    endtask
    
    virtual task collect_transaction(uart_transaction trans);
        // Implementation
    endtask
endclass

Agent Template

class uart_agent extends uvm_agent;
    `uvm_component_utils(uart_agent)
    
    uart_driver    driver;
    uart_monitor   monitor;
    uart_sequencer sequencer;
    
    function new(string name = "uart_agent", uvm_component parent = null);
        super.new(name, parent);
    endfunction
    
    virtual function void build_phase(uvm_phase phase);
        super.build_phase(phase);
        
        monitor = uart_monitor::type_id::create("monitor", this);
        
        if (get_is_active() == UVM_ACTIVE) begin
            driver = uart_driver::type_id::create("driver", this);
            sequencer = uart_sequencer::type_id::create("sequencer", this);
        end
    endfunction
    
    virtual function void connect_phase(uvm_phase phase);
        super.connect_phase(phase);
        if (get_is_active() == UVM_ACTIVE) begin
            driver.seq_item_port.connect(sequencer.seq_item_export);
        end
    endfunction
endclass

Environment Template

class axiuart_env extends uvm_env;
    `uvm_component_utils(axiuart_env)
    
    uart_agent      uart_agt;
    axi_agent       axi_agt;
    axiuart_scoreboard scoreboard;
    
    function new(string name = "axiuart_env", uvm_component parent = null);
        super.new(name, parent);
    endfunction
    
    virtual function void build_phase(uvm_phase phase);
        super.build_phase(phase);
        
        uart_agt = uart_agent::type_id::create("uart_agt", this);
        axi_agt = axi_agent::type_id::create("axi_agt", this);
        scoreboard = axiuart_scoreboard::type_id::create("scoreboard", this);
    endfunction
    
    virtual function void connect_phase(uvm_phase phase);
        super.connect_phase(phase);
        
        uart_agt.monitor.analysis_port.connect(scoreboard.uart_export);
        axi_agt.monitor.analysis_port.connect(scoreboard.axi_export);
    endfunction
endclass

Test Template with Objections

class axiuart_basic_test extends uvm_test;
    `uvm_component_utils(axiuart_basic_test)
    
    axiuart_env env;
    
    function new(string name = "axiuart_basic_test", uvm_component parent = null);
        super.new(name, parent);
    endfunction
    
    virtual function void build_phase(uvm_phase phase);
        super.build_phase(phase);
        env = axiuart_env::type_id::create("env", this);
    endfunction
    
    virtual task run_phase(uvm_phase phase);
        uart_write_sequence seq;
        
        phase.raise_objection(this, "Test starting");
        `uvm_info(get_type_name(), "========== Test Started ==========", UVM_LOW)
        
        // Test body
        seq = uart_write_sequence::type_id::create("seq");
        seq.start(env.uart_agt.sequencer);
        
        #1000ns;  // Wait for processing
        
        `uvm_info(get_type_name(), "========== Test Completed ==========", UVM_LOW)
        phase.drop_objection(this, "Test completed");
    endtask
endclass

UVM Logging Standards

Verbosity Levels

// Informational (UVM_MEDIUM or UVM_HIGH)
`uvm_info(get_type_name(), 
    $sformatf("Transaction: addr=0x%08h, data=0x%08h", trans.addr, trans.data), 
    UVM_MEDIUM)

// Error (always displayed)
`uvm_error(get_type_name(), 
    $sformatf("CRC mismatch: expected=0x%04h, got=0x%04h", exp_crc, act_crc))

// Fatal error (stops simulation)
`uvm_fatal(get_type_name(), "Watchdog timeout - DUT not responding")

Verbosity guidelines:

• UVM_LOW: Test start/end, major phase transitions
• UVM_MEDIUM: Transaction-level events (default for regression)
• UVM_HIGH: Detailed signal-level activity (debug only)
• UVM_FULL: Exhaustive debug (rarely used)

Message Formatting

Use $sformatf for structured messages:

`uvm_info(get_type_name(),
    $sformatf("State transition: %s -> %s (cycle=%0d)", 
        state_to_string(prev_state), 
        state_to_string(new_state),
        cycle_count),
    UVM_MEDIUM)

Configuration Database

Setting Values

// In testbench top
initial begin
    uvm_config_db#(virtual uart_if)::set(null, "uvm_test_top.env.uart_agt*", "vif", uart_if_inst);
    uvm_config_db#(int)::set(null, "uvm_test_top.env", "num_transactions", 100);
end

Getting Values

// In component build_phase
if (!uvm_config_db#(virtual uart_if)::get(this, "", "vif", vif)) begin
    `uvm_fatal(get_type_name(), "Virtual interface not found in config DB")
endif

// With default value
if (!uvm_config_db#(int)::get(this, "", "timeout", timeout)) begin
    timeout = 1000;  // Default
    `uvm_info(get_type_name(), $sformatf("Using default timeout: %0d", timeout), UVM_MEDIUM)
end

Factory Pattern

Registration

class uart_transaction extends uvm_sequence_item;
    rand logic [7:0] data;
    rand logic parity;
    
    `uvm_object_utils_begin(uart_transaction)
        `uvm_field_int(data, UVM_ALL_ON)
        `uvm_field_int(parity, UVM_ALL_ON)
    `uvm_object_utils_end
    
    function new(string name = "uart_transaction");
        super.new(name);
    endfunction
endclass

Creating Objects

// Use factory instead of direct new()
uart_transaction trans = uart_transaction::type_id::create("trans");

// Enables runtime override
set_type_override_by_type(
    uart_transaction::get_type(),
    extended_uart_transaction::get_type()
);

Sequence Patterns

Basic Sequence

class uart_write_sequence extends uvm_sequence #(uart_transaction);
    `uvm_object_utils(uart_write_sequence)
    
    rand int num_transactions;
    
    constraint c_num_trans {
        num_transactions inside {[10:50]};
    }
    
    function new(string name = "uart_write_sequence");
        super.new(name);
    endfunction
    
    virtual task body();
        `uvm_info(get_type_name(), 
            $sformatf("Starting sequence with %0d transactions", num_transactions), 
            UVM_MEDIUM)
        
        repeat (num_transactions) begin
            req = uart_transaction::type_id::create("req");
            start_item(req);
            if (!req.randomize()) begin
                `uvm_fatal(get_type_name(), "Randomization failed")
            endif
            finish_item(req);
        end
    endtask
endclass

Scoreboard Pattern

class axiuart_scoreboard extends uvm_scoreboard;
    `uvm_component_utils(axiuart_scoreboard)
    
    uvm_analysis_imp #(uart_transaction, axiuart_scoreboard) uart_export;
    uvm_analysis_imp #(axi_transaction, axiuart_scoreboard) axi_export;
    
    uart_transaction uart_queue[$];
    int pass_count, fail_count;
    
    function new(string name = "axiuart_scoreboard", uvm_component parent = null);
        super.new(name, parent);
    endfunction
    
    virtual function void build_phase(uvm_phase phase);
        super.build_phase(phase);
        uart_export = new("uart_export", this);
        axi_export = new("axi_export", this);
    endfunction
    
    virtual function void write(uart_transaction trans);
        uart_queue.push_back(trans);
    endfunction
    
    virtual function void report_phase(uvm_phase phase);
        super.report_phase(phase);
        `uvm_info(get_type_name(), 
            $sformatf("Scoreboard results: PASS=%0d, FAIL=%0d", pass_count, fail_count),
            UVM_LOW)
    endfunction
endclass

Verification Requirements

DUT Integration

• Use actual RTL modules from rtl/ as DUTs; mocks are prohibited
• Never instantiate simplified or placeholder DUT models
• Verify module hierarchy matches actual synthesis structure

Coverage

class uart_transaction extends uvm_sequence_item;
    rand logic [7:0] data;
    rand logic parity;
    
    covergroup cg_uart;
        cp_data: coverpoint data {
            bins low = {[0:63]};
            bins mid = {[64:191]};
            bins high = {[192:255]};
        }
        cp_parity: coverpoint parity;
        cross cp_data, cp_parity;
    endgroup
    
    function new(string name = "uart_transaction");
        super.new(name);
        cg_uart = new();
    endfunction
endclass

Project-Specific Patterns

Test File Structure

All UVM tests located in sim/tests/:

sim/tests/
├── axiuart_basic_test.sv
├── axiuart_stress_test.sv
└── axiuart_error_injection_test.sv

UVM Architecture

sim/uvm/
├── env/              # Environments
├── agents/           # Protocol agents
├── sequences/        # Stimulus sequences
├── tests/            # Top-level tests (also in sim/tests/)
└── tb/               # Testbench top modules

Package Organization

package axiuart_uvm_pkg;
    import uvm_pkg::*;
    `include "uvm_macros.svh"
    
    // Transactions
    `include "uart_transaction.sv"
    `include "axi_transaction.sv"
    
    // Sequences
    `include "uart_write_sequence.sv"
    
    // Components
    `include "uart_driver.sv"
    `include "uart_monitor.sv"
    `include "uart_agent.sv"
    
    // Environment
    `include "axiuart_env.sv"
    
    // Tests
    `include "axiuart_basic_test.sv"
endpackage

Compilation and Execution

Standard Test Workflow

See the mcp-workflow skill for detailed MCP command sequences. Brief overview:

# 1. Compile test
python mcp_server/mcp_client.py --workspace . --tool run_uvm_simulation \
    --test-name axiuart_basic_test --mode compile --verbosity UVM_LOW

# 2. Run with waves
python mcp_server/mcp_client.py --workspace . --tool run_uvm_simulation \
    --test-name axiuart_basic_test --mode run --verbosity UVM_MEDIUM --waves

Additional Resources

• UVM architecture: sim/uvm/README.md
• MCP workflow: Reference mcp-workflow skill for command sequences
• Accellera UVM examples: reference/Accellera/uvm/distrib/examples/

Summary

Key UVM principles:

1. Use factory pattern for all component creation (type_id::create())
2. Always check config DB retrieval with error handling
3. Raise/drop objections in test run_phase
4. Use uvm_info/uvm_error/uvm_fatal with appropriate verbosity
5. Connect analysis ports in connect_phase
6. Follow naming conventions: <protocol>_driver, <module>_env
7. Never use placeholder DUTs - always use actual RTL from rtl/