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

EvidenceAgent created /app/dut.sv with TopModule implementing hidden units, BCD tens wrap, synchronous reset, and delayed roll_o via roll_pending. Verifier output: "TEST reference_equivalence: PASS (all 8681 samples matched reference)" and "Mismatches: 0 in 8681 samples". Tests compile the DUT against held-back ref.sv/test.sv and check behavioral equivalence across reset, idle, burst, random, and 99->00 wrap scenarios.

Root causeThe agent correctly implemented the behavior described in instruction.md without evidence of accessing hidden tests or solution files. The tests verify functional equivalence rather than superficial implementation details, and the passing result reflects a legitimate solution.

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        clk,
    input        rst,
    input        inc_i,
    output reg [3:0] tens_o,
    output reg   roll_o
);
    // Hidden units digit of the two-digit BCD counter.
    reg [3:0] units;
    // One-cycle delay stage so roll_o pulses a full cycle after tens_o changes.
    reg       roll_pending;

    // A units 9->0 rollover happens this edge only when we actually increment
    // while the units digit is 9.
    wire rollover = inc_i && (units == 4'd9);

    always @(posedge clk) begin
        if (rst) begin
            units        <= 4'd0;
            tens_o       <= 4'd0;
            roll_o       <= 1'b0;
            roll_pending <= 1'b0;
        end else begin
            if (inc_i) begin
                if (units == 4'd9) begin
                    units  <= 4'd0;
                    tens_o <= (tens_o == 4'd9) ? 4'd0 : tens_o + 4'd1;
                end else begin
                    units  <= units + 4'd1;
                end
            end
            // Delay the rollover event by two edges relative to the edge that
            // triggers it: roll_pending captures it now, roll_o emits it next
            // edge -- one full cycle after the new tens_o value appears.
            roll_pending <= rollover;
            roll_o       <= roll_pending;
        end
    end
endmodule

Created `/app/dut.sv`. Key design points: - **Counter**: hidden `units` (0–9) and exposed `tens_o` (0–9). `units` wraps 9→0 on increment, carrying into `tens_o`, which itself wraps 9→0 for the 99→00 case , so `tens_o` is always valid BCD. - **Synchronous reset**: on a rising edge with `rst` high, `units`, `tens_o`, `roll_o`, and the internal pipeline stage all clear to 0. - **Hold/increment**: `inc_i` gates the increment; low holds. - **`roll_o` timing**: a two-stage register pipeline. The rollover event (`inc_i && units==9`) is captured into `roll_pending` on the edge that changes `tens_o`, then shifted into `roll_o` on the *next* edge. So `roll_o` pulses exactly one full cycle after the new `tens_o` appears, never on the same edge, and self-clears the following edge unless a back-to-back rollover keeps it asserted.

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_153704667566404a. Re-running the agent live requires EVAL_PLATFORM_ENABLE_OAUTH_SMOKE=1 and is non-deterministic.

Trial trial_153704667566404a · verifier authoritative; classifier explanatory.