Configuration Database (uvm_config_db)

The uvm_config_db is UVM's centralized configuration mechanism. It lets any component store and retrieve values — virtual interfaces, parameters, configuration objects — without direct references.

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The API

Setting a value:

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uvm_config_db#(type)::set(context, instance_path, field_name, value);

Getting a value:

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uvm_config_db#(type)::get(context, instance_path, field_name, variable);

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Example 1: Passing the Virtual Interface

The most common use — passing the DUT interface from the top module to UVM components:

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// ── Top module (sets the interface) ──
module tb_top;
    logic clk;
    apb_if vif(clk);

    // Instantiate DUT
    dut u_dut (.clk(clk), .psel(vif.PSEL), /* ... */);

    initial begin
        // Store the interface in config_db
        uvm_config_db#(virtual apb_if)::set(
            null,                          // null = global
            "uvm_test_top.env.agent*",     // who can see it
            "vif",                         // field name
            vif                            // the value
        );
        run_test();
    end
endmodule

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// ── Driver (gets the interface) ──
function void build_phase(uvm_phase phase);
    super.build_phase(phase);
    if (!uvm_config_db#(virtual apb_if)::get(this, "", "vif", vif))
        `uvm_fatal("NOVIF", "Virtual interface not found!")
endfunction

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Example 2: Configuration Objects

For complex configurations, create a config object:

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class apb_agent_config extends uvm_object;
    `uvm_object_utils(apb_agent_config)

    int            num_transactions = 100;
    bit            enable_coverage  = 1;
    bit            enable_checking  = 1;
    bit [31:0]     base_address     = 32'h0;

    function new(string name = "apb_agent_config");
        super.new(name);
    endfunction
endclass

Set it from the test:

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class my_test extends uvm_test;
    function void build_phase(uvm_phase phase);
        super.build_phase(phase);

        apb_agent_config cfg = apb_agent_config::type_id::create("cfg");
        cfg.num_transactions = 500;
        cfg.enable_coverage  = 1;

        uvm_config_db#(apb_agent_config)::set(
            this, "env.agent*", "cfg", cfg
        );
    endfunction
endclass

Retrieve it in the agent:

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class apb_agent extends uvm_agent;
    apb_agent_config cfg;

    function void build_phase(uvm_phase phase);
        super.build_phase(phase);
        if (!uvm_config_db#(apb_agent_config)::get(this, "", "cfg", cfg))
            `uvm_fatal("NOCFG", "Agent config not found!")
    endfunction
endclass

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Scoping Rules

The instance_path controls which components can see the value:

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Debugging config_db

Dump all entries:

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uvm_config_db#(virtual apb_if)::dump();

Command-line trace:

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+UVM_CONFIG_DB_TRACE

This prints every set and get call with full path information.

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Common Pitfalls

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Best Practices

• Use config objects instead of many individual set/get calls.
• Always \uvm_fatal on get failure for required configurations.
• Set values at the highest appropriate level (test → env → agent).
• Use null context for truly global values (virtual interfaces from top module).