uvm_config_db Architecture

static function void set(
uvm_component  cntxt,       // who is setting (null = from module scope)
string          inst_name,   // hierarchical path pattern (wildcards OK)
string          field_name,  // string key — must match get() exactly
T               value        // the data to store (type T = parameterised)
);

// ── From tb_top (module, NOT a component — use null cntxt) ───────────
initial begin
// Scope: "" + "uvm_test_top.*" = "uvm_test_top.*"
// Visible to: every component under uvm_test_top
uvm_config_db#(virtual apb_if)::set(
null,                 // cntxt: null because tb_top is a module
"uvm_test_top.*",     // inst_name: wildcard — all components under root
"apb_vif",            // field_name: the lookup key
apb_vif               // value: the interface instance
);
run_test();
end
 
// ── From base_test (component — use 'this') ───────────────────────────
function void build_phase(uvm_phase phase);
super.build_phase(phase);
// Scope: "uvm_test_top" + "*.apb_agent" = "uvm_test_top.*.apb_agent"
// Visible to: any apb_agent component anywhere under the test
uvm_config_db#(int)::set(
this,             // cntxt: 'this' = uvm_test_top (the test component)
"*.apb_agent",    // inst_name: any apb_agent under this test
"num_txns",        // field_name
200               // value
);
endfunction
 
// ── From my_env (narrower scope) ──────────────────────────────────────
function void build_phase(uvm_phase phase);
super.build_phase(phase);
// Scope: "uvm_test_top.env" + "apb_agent_0.*"
// Visible to: ONLY components under apb_agent_0 in THIS env
uvm_config_db#(bit)::set(
this, "apb_agent_0.*", "is_active", 1'b1
);
endfunction

static function bit get(
uvm_component  cntxt,       // the component doing the getting ('this')
string          inst_name,   // usually "" — appended to cntxt's path
string          field_name,  // must exactly match the set() field_name
ref T           value        // output — populated on success
);  // returns 1 if found, 0 if not found — ALWAYS check the return value
 
// ── Standard get() pattern with mandatory error handling ─────────────
class apb_driver extends uvm_driver #(apb_seq_item);
`uvm_component_utils(apb_driver)
virtual apb_if vif;
 
function void build_phase(uvm_phase phase);
super.build_phase(phase);
 
// cntxt = this (driver at "uvm_test_top.env.apb_agent.drv")
// inst_name = "" (no additional path — look up for 'this' component)
// field_name must match what was set() exactly
if (!uvm_config_db#(virtual apb_if)::get(this, "", "apb_vif", vif))
`uvm_fatal("CFG",
"apb_vif not found in config_db — check tb_top set() call")
 
// If get() returned 0, uvm_fatal stops simulation — no null pointer crash later
endfunction
endclass
 
// ── Getting a simple integer ──────────────────────────────────────────
int num_txns = 100;   // default value
void'(uvm_config_db#(int)::get(this, "", "num_txns", num_txns));
// void'() suppresses "return value ignored" warning when absence is acceptable

// ── SET side: scope key construction ─────────────────────────────────
// set(cntxt, inst_name, field_name, value)
// Scope key = cntxt.get_full_name() + "." + inst_name
//           = "" + "uvm_test_top.*"   (null cntxt has empty path)
//           = "uvm_test_top.*"
uvm_config_db#(virtual apb_if)::set(null, "uvm_test_top.*", "apb_vif", vif_h);
 
// ── GET side: lookup key construction ────────────────────────────────
// get(cntxt, inst_name, field_name, value)
// Lookup key = cntxt.get_full_name() + "." + inst_name  (if inst_name not empty)
//           = "uvm_test_top.env.apb_agent.drv" + "." + ""
//           = "uvm_test_top.env.apb_agent.drv"
uvm_config_db#(virtual apb_if)::get(this, "", "apb_vif", vif);
 
// ── Matching: does "uvm_test_top.*" cover "uvm_test_top.env.apb_agent.drv"?
// Pattern:  "uvm_test_top.*"
// Key:      "uvm_test_top.env.apb_agent.drv"
// The wildcard * matches ".env.apb_agent.drv" → MATCH → get() returns 1 ✓
 
// ── Narrower scope example ────────────────────────────────────────────
// If set was called as:
uvm_config_db#(virtual apb_if)::set(null, "uvm_test_top.env.apb_agent_0.*", "apb_vif", vif0);
// Scope: "uvm_test_top.env.apb_agent_0.*"
// Covers: any component under apb_agent_0 only
// drv under apb_agent_1 → "uvm_test_top.env.apb_agent_1.drv" → NO MATCH

// ────────────────────────────────────────────────────────────────────
// tb_top.sv  — the module that owns the interface
// ────────────────────────────────────────────────────────────────────
module tb_top;
`include "uvm_macros.svh"
import uvm_pkg::*;
import test_pkg::*;
 
// Interface instances
apb_if  apb_vif();   // creates the interface
my_dut  dut (.apb(apb_vif));   // DUT connection
 
initial begin
// Store handle BEFORE run_test() — run_test() triggers build_phase
uvm_config_db#(virtual apb_if)::set(
null,               // null because tb_top is a module, not uvm_component
"uvm_test_top.*",   // visible to ALL components under the test root
"apb_vif",          // the key — exactly this string must be used in get()
apb_vif             // the interface instance — modport not needed here
);
run_test();   // UVM takes over — build_phase cascade begins
end
endmodule
 
// ────────────────────────────────────────────────────────────────────
// apb_driver.sv  — the component that needs the interface
// ────────────────────────────────────────────────────────────────────
class apb_driver extends uvm_driver #(apb_seq_item);
`uvm_component_utils(apb_driver)
virtual apb_if vif;   // will hold the interface handle after build_phase
 
function new(string name, uvm_component parent);
super.new(name, parent);
endfunction
 
function void build_phase(uvm_phase phase);
super.build_phase(phase);
// Retrieve the interface — fatal if not found
if (!uvm_config_db#(virtual apb_if)::get(
this,      // 'this' = drv at "uvm_test_top.env.apb_agent.drv"
"",        // no additional path — lookup for 'this' component
"apb_vif", // must match the set() key exactly
vif))      // populated on success
`uvm_fatal("CFG", "apb_vif not found — check tb_top set() call")
endfunction
 
task run_phase(uvm_phase phase);
// vif is now valid — safe to drive signals
@(posedge vif.clk);
vif.paddr  = req.addr;
vif.pwdata = req.data;
endtask
endclass

// ── Step 1: Define the configuration class ────────────────────────────
class apb_agent_config extends uvm_object;
`uvm_object_utils(apb_agent_config)   // register with factory (good practice)
 
// Interface handle — part of the config object
virtual apb_if   vif;
 
// Behavioural parameters
int              num_txns    = 100;
bit              is_active   = 1;   // 1 = active (driver+monitor), 0 = passive (monitor only)
int              max_wait_cycles = 20;
 
function new(string name = "apb_agent_config");
super.new(name);
endfunction
endclass
 
// ── Step 2: Create and set from tb_top or test ────────────────────────
initial begin
apb_agent_config cfg = new("cfg");   // or use factory create
cfg.vif            = apb_vif;          // attach the virtual interface
cfg.num_txns       = 500;
cfg.is_active      = 1;
cfg.max_wait_cycles = 10;
 
uvm_config_db#(apb_agent_config)::set(
null, "uvm_test_top.env.apb_agent", "cfg", cfg
);
run_test();
end
 
// ── Step 3: Retrieve in the agent's build_phase ───────────────────────
class apb_agent extends uvm_agent;
`uvm_component_utils(apb_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("CFG", "apb_agent_config not found")
 
// cfg is now populated — pass it down to driver and monitor
drv = apb_driver::type_id::create("drv", this);
uvm_config_db#(apb_agent_config)::set(this, "drv", "cfg", cfg);
endfunction
apb_driver        drv;
endclass

// ── The four arguments ────────────────────────────────────────────────
//   set(cntxt, inst_name, field_name, value)
//   get(cntxt, inst_name, field_name, value)  ← returns bit (1=found)
//
//   cntxt     : who is setting/getting. null from module. 'this' from component.
//   inst_name : path suffix appended to cntxt's full_name. Wildcards OK.
//   field_name: string key. Case-sensitive. Must match exactly.
//   value     : the data (type T = the parameterised class argument)
 
// ── Scope key formula ─────────────────────────────────────────────────
//   set scope = cntxt.get_full_name() + "." + inst_name
//   get key   = cntxt.get_full_name() + "." + inst_name
//   Match if: the set scope pattern covers the get key path
 
// ── Essential rules ───────────────────────────────────────────────────
//   1. set() before run_test() for interfaces (needed in build_phase)
//   2. Always check get() return value for critical data
//   3. Type T in set() and get() must be IDENTICAL
//   4. field_name must match EXACTLY — case, spelling, no spaces
//   5. For debug: add +UVM_CONFIG_DB_TRACE to simulation command
 
// ── Debug trace output format ─────────────────────────────────────────
//   vsim +UVM_CONFIG_DB_TRACE work.tb_top
//
//   UVM_INFO: SET uvm_config_db #(virtual apb_if) ...
//     by: null  context: uvm_test_top.*  field: apb_vif
//   UVM_INFO: GET uvm_config_db #(virtual apb_if) ...
//     by: uvm_test_top.env.apb_agent.drv  field: apb_vif  result: HIT

`include "uvm_macros.svh"
import uvm_pkg::*;
 
// ── Consumer: component that reads config ──────────────────────────
class my_monitor extends uvm_monitor;
`uvm_component_utils(my_monitor)
int num_checks = 10;   // default value
 
function new(string n, uvm_component p); super.new(n,p); endfunction
 
function void build_phase(uvm_phase phase);
super.build_phase(phase);
// Retrieve config — override default if found
if(!uvm_config_db#(int)::get(this, "", "num_checks", num_checks))
`uvm_info("CFG", "num_checks not found, using default=10", UVM_MEDIUM)
else
`uvm_info("CFG", $sformatf("num_checks=%0d", num_checks), UVM_MEDIUM)
endfunction
endclass
 
// ── Provider: test that sets config ────────────────────────────────
class basic_cfg_test extends uvm_test;
`uvm_component_utils(basic_cfg_test)
my_monitor mon;
function new(string n, uvm_component p); super.new(n,p); endfunction
 
function void build_phase(uvm_phase phase);
// Set BEFORE creating the component so it sees the value in its build_phase
uvm_config_db#(int)::set(this, "mon", "num_checks", 50);
super.build_phase(phase);
mon = my_monitor::type_id::create("mon", this);
endfunction
 
task run_phase(uvm_phase p);
p.raise_objection(this); p.drop_objection(this);
endtask
endclass
 
module basic_cfg_top;
initial run_test("basic_cfg_test");
endmodule
 
// Expected Output:
// UVM_INFO [CFG] num_checks=50   ← config_db value overrides default

`include "uvm_macros.svh"
import uvm_pkg::*;
 
// Interface definition (normally in a separate .sv file) ──────────
interface apb_if (input logic clk);
logic[31:0] paddr;
logic[31:0] pwdata;
logic        pwrite;
logic        psel;
logic        penable;
logic        pready;
endinterface
 
// Driver reads vif from config_db ──────────────────────────────────
class apb_driver extends uvm_driver#(uvm_sequence_item);
`uvm_component_utils(apb_driver)
virtual apb_if vif;
 
function new(string n, uvm_component p); super.new(n,p); endfunction
 
function void build_phase(uvm_phase phase);
super.build_phase(phase);
// Fatal if vif not set — driver cannot function without it
if(!uvm_config_db#(virtual apb_if)::get(this, "", "vif", vif))
`uvm_fatal("CFG", "Virtual interface 'vif' not set in config_db")
else
`uvm_info("CFG", "vif connected successfully", UVM_MEDIUM)
endfunction
endclass
 
// Top module wires interface and sets it in config_db ──────────────
module apb_tb_top;
logic clk;
initial clk = 0;
always #5 clk = ~clk;
 
apb_if dut_if(.clk(clk));   // interface instance
 
initial begin
// Set BEFORE run_test — driver needs it in build_phase
uvm_config_db#(virtual apb_if)::set(null, "uvm_test_top.*", "vif", dut_if);
run_test("apb_test");
end
endmodule
 
// Key points:
// 1. null context + wildcard path = accessible from any component
// 2. set() called BEFORE run_test() so it's available in build_phase
// 3. uvm_fatal ensures the driver can't silently run with a null interface

`include "uvm_macros.svh"
import uvm_pkg::*;
 
// Config object: one object, multiple parameters ───────────────────
class apb_agent_config extends uvm_object;
`uvm_object_utils_begin(apb_agent_config)
`uvm_field_int(is_active,    UVM_ALL_ON)
`uvm_field_int(num_txns,     UVM_ALL_ON)
`uvm_field_int(bus_width,    UVM_ALL_ON)
`uvm_object_utils_end
 
bit  is_active  = 1;       // 1=active agent, 0=passive monitor only
int  num_txns   = 100;     // number of transactions to generate
int  bus_width  = 32;      // APB bus width in bits
 
function new(string n="apb_agent_config"); super.new(n); endfunction
endclass
 
class apb_agent extends uvm_agent;
`uvm_component_utils(apb_agent)
apb_agent_config cfg;
 
function new(string n, uvm_component p); super.new(n,p); endfunction
 
function void build_phase(uvm_phase phase);
super.build_phase(phase);
if(!uvm_config_db#(apb_agent_config)::get(this, "", "cfg", cfg))
`uvm_fatal("CFG", "apb_agent_config not found")
 
`uvm_info("CFG", $sformatf(
"active=%0b txns=%0d width=%0d",
cfg.is_active, cfg.num_txns, cfg.bus_width), UVM_MEDIUM)
endfunction
endclass
 
class cfg_obj_test extends uvm_test;
`uvm_component_utils(cfg_obj_test)
apb_agent        agent;
apb_agent_config cfg;
function new(string n, uvm_component p); super.new(n,p); endfunction
 
function void build_phase(uvm_phase phase);
cfg = apb_agent_config::type_id::create("cfg");
cfg.is_active = 1;
cfg.num_txns  = 250;
cfg.bus_width = 32;
 
uvm_config_db#(apb_agent_config)::set(this, "agent", "cfg", cfg);
super.build_phase(phase);
agent = apb_agent::type_id::create("agent", this);
endfunction
 
task run_phase(uvm_phase p);
p.raise_objection(this); p.drop_objection(this);
endtask
endclass
 
module cfg_obj_top;
initial run_test("cfg_obj_test");
endmodule
 
// Expected Output:
// [CFG] active=1 txns=250 width=32   ← all three fields from config object

`include "uvm_macros.svh"
import uvm_pkg::*;
 
class scope_consumer extends uvm_component;
`uvm_component_utils(scope_consumer)
int timeout;
function new(string n, uvm_component p); super.new(n,p); endfunction
function void build_phase(uvm_phase phase);
super.build_phase(phase);
void'(uvm_config_db#(int)::get(this, "", "timeout", timeout));
$display("  [%s] timeout=%0d", get_full_name(), timeout);
endfunction
endclass
 
class scope_test extends uvm_test;
`uvm_component_utils(scope_test)
scope_consumer c1, c2;
function new(string n, uvm_component p); super.new(n,p); endfunction
 
function void build_phase(uvm_phase phase);
// Wildcard: applies to all children
uvm_config_db#(int)::set(this, "*", "timeout", 100);
// Exact path: overrides wildcard for c2 specifically
uvm_config_db#(int)::set(this, "c2", "timeout", 500);
super.build_phase(phase);
c1 = scope_consumer::type_id::create("c1", this);
c2 = scope_consumer::type_id::create("c2", this);
endfunction
task run_phase(uvm_phase p);
p.raise_objection(this); p.drop_objection(this);
endtask
endclass
 
module scope_top;
initial run_test("scope_test");
endmodule
 
// Expected Output:
//   [uvm_test_top.c1] timeout=100   ← wildcard applied
//   [uvm_test_top.c2] timeout=500   ← exact path overrides wildcard
//
// Key insight: More specific path wins. "c2" is more specific than "*".

// ❌ WRONG: type mismatch between set and get
// In test:
uvm_config_db#(int)::set(this, "mon", "timeout", 100);   // stores as 'int'
 
// In monitor:
bit[31:0] timeout;
uvm_config_db#(bit[31:0])::get(this, "", "timeout", timeout);
// get() returns 0 — different type = different entry in database
// timeout remains at its initialization value, no warning
 
// ✓ CORRECT: matching types
uvm_config_db#(int)::set(this, "mon", "timeout", 100);
 
int timeout;   // ← same type as set()
if(!uvm_config_db#(int)::get(this, "", "timeout", timeout))
`uvm_error("CFG", "timeout not found in config_db")
 
// Debug: add +UVM_CONFIG_DB_TRACE to simulation command
// It shows every set/get call with types and paths — type mismatches are obvious

// ❌ WRONG: path doesn't reach the deep component
// Testbench topology: test → env → agent → driver
// Component full path: "uvm_test_top.env.agent.drv"
 
// In test.build_phase:
uvm_config_db#(int)::set(this, "drv", "speed", 100);
// set scope = "uvm_test_top.drv" ← WRONG, driver is at "...env.agent.drv"
 
// ✓ FIX 1: Use wildcard to reach any level
uvm_config_db#(int)::set(this, "env.agent.drv", "speed", 100);
 
// ✓ FIX 2: Global wildcard — reaches all components named "drv"
uvm_config_db#(int)::set(null, "uvm_test_top.*", "speed", 100);
 
// Debug: print the consumer's path INSIDE get():
// `uvm_info("CFG", $sformatf("my path: %s", get_full_name()), UVM_DEBUG)
// Use +UVM_CONFIG_DB_TRACE to see scope resolution in real time

// ================================================================
// config_db_demo.sv — config_db Architecture Demonstration
// Covers: integer, string, scope, wildcard, config object
//
// Compile (Questa):
//   vlog -sv -L uvm_1_2 config_db_demo.sv
//   vsim -c -L uvm_1_2 config_db_demo_top -do "run -all; quit"
//
// Compile (VCS):
//   vcs -sverilog -ntb_opts uvm-1.2 config_db_demo.sv && ./simv
//
// Compile (Xcelium):
//   xrun -sv -uvm config_db_demo.sv
//
// Debug mode (any simulator):
//   Add +UVM_CONFIG_DB_TRACE to see all set/get operations
// ================================================================
 
`include "uvm_macros.svh"
import uvm_pkg::*;
 
// ── Config object ──────────────────────────────────────────────────
class agent_cfg extends uvm_object;
`uvm_object_utils(agent_cfg)
int    max_txns  = 100;
string protocol  = "APB";
bit    is_active = 1;
function new(string n="agent_cfg"); super.new(n); endfunction
endclass
 
// ── Generic consumer component ─────────────────────────────────────
class demo_comp extends uvm_component;
`uvm_component_utils(demo_comp)
 
int        num_pkts = 10;     // integer config
string     mode     = "SLOW";  // string config
agent_cfg  cfg;                // object config
 
function new(string n, uvm_component p); super.new(n,p); endfunction
 
function void build_phase(uvm_phase phase);
super.build_phase(phase);
// Get all three config items
void'(uvm_config_db#(int)::get(this, "", "num_pkts", num_pkts));
void'(uvm_config_db#(string)::get(this, "", "mode", mode));
void'(uvm_config_db#(agent_cfg)::get(this, "", "cfg", cfg));
 
$display("  [%s] num_pkts=%0d mode=%s", get_name(), num_pkts, mode);
if(cfg != null)
$display("  [%s] cfg: max_txns=%0d protocol=%s active=%0b",
get_name(), cfg.max_txns, cfg.protocol, cfg.is_active);
else
$display("  [%s] cfg: not set", get_name());
endfunction
endclass
 
// ── Test: sets different configs for two components ─────────────────
class full_demo_test extends uvm_test;
`uvm_component_utils(full_demo_test)
demo_comp  c_alpha, c_beta;
agent_cfg  cfg_a;
 
function new(string n, uvm_component p); super.new(n,p); endfunction
 
function void build_phase(uvm_phase phase);
// ── Integer: wildcard applies to all children ──────────
uvm_config_db#(int)::set(this, "*", "num_pkts", 50);
 
// ── String: per-component exact path ───────────────────
uvm_config_db#(string)::set(this, "c_alpha", "mode", "FAST");
uvm_config_db#(string)::set(this, "c_beta",  "mode", "SAFE");
 
// ── Config object: only c_alpha gets one ───────────────
cfg_a = agent_cfg::type_id::create("cfg_a");
cfg_a.max_txns  = 200;
cfg_a.protocol  = "AXI";
cfg_a.is_active = 1;
uvm_config_db#(agent_cfg)::set(this, "c_alpha", "cfg", cfg_a);
 
super.build_phase(phase);
c_alpha = demo_comp::type_id::create("c_alpha", this);
c_beta  = demo_comp::type_id::create("c_beta",  this);
endfunction
 
task run_phase(uvm_phase phase);
phase.raise_objection(this);
phase.drop_objection(this);
endtask
endclass
 
module config_db_demo_top;
initial run_test("full_demo_test");
endmodule
 
// ================================================================
// Expected Output:
//
//   [c_alpha] num_pkts=50 mode=FAST
//   [c_alpha] cfg: max_txns=200 protocol=AXI active=1
//
//   [c_beta]  num_pkts=50 mode=SAFE
//   [c_beta]  cfg: not set
//
// Analysis:
//   num_pkts=50:   wildcard "*" set applies to both
//   mode=FAST/SAFE: exact paths set different values per component
//   cfg: only c_alpha received it; c_beta gets null → "not set"
// ================================================================