SyncVals · Trajectory

bcd-tens-rollover

claude-code claude-opus-4-8 ✓ resolved GOOD_SUCCESS ↑ View task

Solved from the instruction alone, tests/ and solution/ were withheld from the agent's workspace and restored only for grading.

Reward = tests/test.sh exit code (0 → resolved); the classification below is post-hoc and cannot change it.

Classification , post-hoc; cannot change the reward

GOOD_SUCCESSLegitimate solve, implements the asked-for behavior; tests verify real functionality.

SubtypeLegitimate Solution

EvidenceInstruction required `roll_o` to pulse one full cycle after a units 9->0 rollover and clear on reset. Agent wrote `/app/dut.sv` with `always_ff @(posedge clk)`, synchronous `if (rst)` clearing `units`, `tens_o`, `roll_o`, and `roll_d`, BCD rollover logic for `units == 4'd9`, and `roll_o <= roll_d` with `roll_d <= 1'b1` only on rollover. Verifier output: `TEST reference_equivalence: PASS (all 8681 samples matched reference)` and reward=1.0.

Root causeThe agent implemented the specified two-digit BCD tens counter and delayed registered rollover pulse directly from the instruction. The tests compare behavior against a reference across resets, idle periods, continuous increments, random streams, and 99->00 wrap, and the implementation matched all samples without evidence of hidden test or solution access.

RecommendationN/A - task is fine

Trajectory

Tool-by-tool agent trajectory

1 tool calls · 1 tool types · 3 steps

Write /app/dut.sv defining TopModule with ports clk, rst, inc_i, tens_o[3:0], and roll_o; rst is synchronous active high. Track a two-digit BCD counter from 00 through 99, but expose only the tens digit. On a rising clock with rst high, clear the hidden units digit, tens_o, and roll_o to 0. On any other rising edge with inc_i high, increment the counter once; with inc_i low, hold the count. When the hidden units digit increments from 9 to 0, increment the tens digit, wrapping 9 to 0 for the 99 to 00 transition. tens_o must always be a valid BCD value 0 through 9. roll_o is registered and pulses for exactly one clock one full cycle after the new tens_o value first appears because of a units 9 to 0 rollover. It must not pulse on the same edge that changes tens_o, and it must clear to 0 on the following edge unless another delayed rollover pulse is due. Helper modules are allowed in the same file. Do not use simulator/file-I/O system tasks, include/define/undef/conditional directives, DPI, force/release, or hidden grader identifiers.

write · /app/dut.sv

module TopModule (
    input  logic       clk,
    input  logic       rst,
    input  logic       inc_i,
    output logic [3:0] tens_o,
    output logic       roll_o
);

    // Hidden units digit of the two-digit BCD counter.
    logic [3:0] units;

    // Delayed rollover flag: set on the edge where tens_o changes,
    // consumed one cycle later to produce the registered roll_o pulse.
    logic       roll_d;

    always_ff @(posedge clk) begin
        if (rst) begin
            units  <= 4'd0;
            tens_o <= 4'd0;
            roll_o <= 1'b0;
            roll_d <= 1'b0;
        end else begin
            // Registered pulse appears one full cycle after tens_o updated.
            roll_o <= roll_d;
            roll_d <= 1'b0;

            if (inc_i) begin
                if (units == 4'd9) begin
                    units <= 4'd0;
                    if (tens_o == 4'd9)
                        tens_o <= 4'd0;
                    else
                        tens_o <= tens_o + 4'd1;
                    roll_d <= 1'b1; // rollover happened this edge
                end else begin
                    units <= units + 4'd1;
                end
            end
        end
    end

endmodule

Created `/app/dut.sv`. **How it meets the spec:** - **Hidden units, exposed tens:** `units[3:0]` is internal; only `tens_o[3:0]` is a port. Both stay valid BCD (0–9) , tens wraps 9→0 on the 99→00 transition. - **Synchronous active-high reset:** on a rising edge with `rst` high, `units`, `tens_o`, `roll_o`, and the internal `roll_d` all clear to 0. - **Increment / hold:** with `inc_i` high, counter advances once per edge; with `inc_i` low, everything holds. - **Delayed one-cycle pulse:** on the edge where a units 9→0 rollover updates `tens_o`, `roll_d` is set (but `roll_o` is *not* pulsed that edge). The next edge copies `roll_d` into `roll_o`, so `roll_o` pulses exactly one full cycle after the new `tens_o` appears, then clears the edge after , unless another rollover made a fresh `roll_d` due. No forbidden constructs (no system tasks, no `include`/`define`, no DPI/force). The counter logic and pulse pipeline live entirely in `TopModule`, so no helper module was needed.

Final diff , what the agent changed

No file changes, the agent left the workspace untouched.

Verifier output , the proof behind the reward

tests/test.sh

TEST dut_present: PASS (/app/dut.sv exists)
TEST dut_forbidden: PASS (no forbidden constructs)
TEST harness_prepare: PASS (harness names nonce-renamed)
TEST dut_compiles: PASS (compiled with held-back reference/testbench)
TEST simulation_completed: PASS (Mismatches: 0 in 8681 samples)
TEST reference_equivalence: PASS (all 8681 samples matched reference)

Reproduce this trial: git checkout 2f94510 && PYTHONPATH=src python3 scripts/build_site.py , then open trial/trial_3e3a66595e7042b2. Re-running the agent live requires EVAL_PLATFORM_ENABLE_OAUTH_SMOKE=1 and is non-deterministic.

Trial trial_3e3a66595e7042b2 · verifier authoritative; classifier explanatory.