Writing Tb

Writing a Testbench

Framework

Use svc_unit.sv from rtl/common/. File location: tb/<category>/ matching the module's rtl location.

Testbench Template

`include "svc_unit.sv"
`include "svc_module_name.sv"

module svc_module_name_tb;
  //
  // Clock and reset
  //
  `TEST_CLK_NS(clk, 10);
  `TEST_RST_N(clk, rst_n);

  //
  // Testbench signals
  //
  logic       in_valid;
  logic [7:0] in_data;
  logic       in_ready;
  logic       out_valid;
  logic [7:0] out_data;
  logic       out_ready;

  //
  // UUT instantiation
  //
  svc_module_name uut (
      .clk      (clk),
      .rst_n    (rst_n),
      .in_valid (in_valid),
      .in_data  (in_data),
      .in_ready (in_ready),
      .out_valid(out_valid),
      .out_data (out_data),
      .out_ready(out_ready)
  );

  //
  // Signal initialization
  //
  always_ff @(posedge clk) begin
    if (~rst_n) begin
      in_valid  <= 1'b0;
      in_data   <= 8'h00;
      out_ready <= 1'b1;
    end
  end

  //
  // Tests
  //
  task automatic test_reset();
    `CHECK_FALSE(out_valid);
    `CHECK_TRUE(in_ready);
  endtask

  task automatic test_basic();
    in_valid = 1'b1;
    in_data  = 8'hA5;
    `TICK(clk);
    `CHECK_WAIT_FOR(clk, out_valid, 10);
    `CHECK_EQ(out_data, 8'hA5);
  endtask

  //
  // Test suite
  //
  `TEST_SUITE_BEGIN(svc_module_name_tb);
  `TEST_CASE(test_reset);
  `TEST_CASE(test_basic);
  `TEST_SUITE_END();
endmodule

Key Macros

Setup

• TEST_CLK_NS(clk, period_ns) - Create clock
• TEST_RST_N(clk, rst_n) - Create reset (active 5 cycles)

Test Organization

• TEST_SUITE_BEGIN(name) - Start test suite
• TEST_SUITE_END() - End test suite
• TEST_CASE(task_name) - Register a test
• TICK(clk) - Advance one clock cycle

Assertions

• CHECK_TRUE(condition) - Verify true
• CHECK_FALSE(condition) - Verify false
• CHECK_EQ(a, b) - Verify equal
• CHECK_NEQ(a, b) - Verify not equal
• CHECK_LT(a, b) / CHECK_GT(a, b) - Comparisons
• CHECK_LTE(a, b) / CHECK_GTE(a, b) - Comparisons
• CHECK_WAIT_FOR(clk, condition, max_cycles) - Wait for condition

Rules

• First test must be reset test - Always test post-reset state
• Use automatic for all tasks - Proper variable scoping
• Initialize all signals in reset block - Use always_ff with ~rst_n
• Use non-blocking assignments (<=) in reset block

Running Tests

make <module>_tb           # Run specific testbench
make <module>_tb RUN=test  # Run specific test case
make tb                    # Run all testbenches

Debugging

VCD files generated at .build/<module>.vcd:

gtkwave .build/<module>.vcd &

Reference

See tb/common/svc_arbiter_tb.sv for a complete example.

For full details see docs/tb.md