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

EvidenceThe agent wrote /app/dut.sv with TopModule, synchronous reset, hidden units digit, tens_o BCD wrap, and delayed roll_o logic: `pending <= rollover; roll_o <= pending;`. Verifier output shows `TEST dut_compiles: PASS`, `TEST simulation_completed: PASS (Mismatches: 0 in 8681 samples)`, and `TEST reference_equivalence: PASS (all 8681 samples matched reference)`. Trajectory shows only a Write to `/app/dut.sv`; no reads of hidden `tests/` or `solution/` artifacts.

Root causeThe task was clearly specified and the agent implemented the required two-digit BCD counter behavior with roll_o pulsing one cycle after tens_o changes. The tests verified behavior against a reference model across directed and random stimulus, and the implementation matched.

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 and the registered rollover delay stage.
    reg [3:0] units;
    reg       pending;

    // A units 9->0 rollover happens this edge when we increment at units==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;
            pending <= 1'b0;
        end else begin
            if (inc_i) begin
                if (units == 4'd9) begin
                    units <= 4'd0;
                    if (tens_o == 4'd9)
                        tens_o <= 4'd0;      // 99 -> 00 wrap
                    else
                        tens_o <= tens_o + 4'd1;
                end else begin
                    units <= units + 4'd1;
                end
            end
            // Two-stage delay so roll_o pulses one full cycle after tens_o
            // changes: rollover (edge T) -> pending (edge T) -> roll_o (edge T+1).
            pending <= rollover;
            roll_o  <= pending;
        end
    end
endmodule

Written `/app/dut.sv`. Design notes: - `units` (hidden) and `tens_o` form the two-digit BCD counter; only `tens_o` is exposed. - `rst` is checked synchronously inside `always @(posedge clk)` and clears everything. - On a non-reset edge, `inc_i` gates the increment; at `units==9` the units wrap to 0 and `tens_o` increments, with 9→0 wrap for the 99→00 case, keeping `tens_o` always a valid 0–9 BCD digit. - `roll_o` uses a **two-stage register delay**: the combinational `rollover` (units 9→0) latches into `pending` at edge T (when `tens_o` changes), then into `roll_o` at edge T+1. So `roll_o` pulses exactly one clock, one full cycle after the new `tens_o` appears , never on the same edge , and clears the following edge unless another delayed rollover is queued. No system tasks, macros, DPI, or force/release were used.

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_b1193180b8034305. Re-running the agent live requires EVAL_PLATFORM_ENABLE_OAUTH_SMOKE=1 and is non-deterministic.

Trial trial_b1193180b8034305 · verifier authoritative; classifier explanatory.