SyncValsverifier → artifact → classifier → verdict
SyncVals · Trajectory

byte-serial-round-scheduler

claude-code claude-opus-4-8 ✗ failed GOOD_FAILURE ↑ 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_FAILUREHonest miss, the agent ran correctly but couldn't solve it. Expected for a hard task; the task is sound.
SubtypeImplementation Bugs
EvidenceVerifier passed setup and simulation but failed behavioral equivalence: `TEST reference_equivalence: FAIL (794 mismatches in 16537 samples)`. The task instruction states `result_valid and ready asserting that cycle` on the finishing key-mix slot, and the reference/testbench compares `{ready_ref, rv_ref, bo_ref}` against the DUT every clock sample. The agent's submitted `/app/dut.sv` sets `result_valid <= 1'b1` on finish but has no default deassertion in the idle/no-start path, so `result_valid` can remain high after the completion cycle.
Root causeThe agent implemented the core transform mostly correctly but missed registered control-signal pulse behavior, causing behavioral mismatches after operations complete. The tests check the specified protocol behavior against a reference model, and this failure is attributable to the agent's implementation, not an underspecified or brittle task.
RecommendationN/A - task is fine
Trajectory
Tool-by-tool agent trajectory
3 tool calls · 2 tool types · 8 steps
A block engine transforms a 128-bit block under a start/ready protocol. Ports (1 bit unless width shown): clk rst_n start block_in 128 round_key0 128 num_rounds 4 reseed reseed_round 4 ready result_valid block_out 128 rst_n is active-low synchronous; while low at a rising edge outputs clear (ready high, result_valid low). start, while ready is high, loads block_in, round_key0 and num_rounds (1-15), else ignored; ready stays low until the finishing key-mix slot. Engine state is 128 bits, seeded by block_in. A round is sixteen byte slots then one key-mix slot. Byte slots visit columns 0 to 3; column c is state bits [32*c+31:32*c], its [31:24] byte first down to [7:0] last. A slot replaces only its byte with rol1(byte xor feedback) xor 8'h63; slot 0's feedback is the round's start feedback, else the previous slot's byte. round_index counts completed rounds. Round 0's start feedback is {4'b0, round_index}; a later round's is fixed at its preceding key-mix slot by reseed there (not reseed during the round): high gives {4'b0, reseed_round}, low {4'b0, round_index}. The key-mix slot xors state with round_key0. On the slot completing num_rounds, block_out becomes that post-xor state, result_valid and ready asserting that cycle; otherwise the next round starts next edge. block_out holds between operations, changing only on a finishing slot. All outputs are registered. Submit plain ASCII Verilog; $ system tasks and define/include directives are rejected. Write TopModule to /app/dut.sv.
I'll analyze the spec carefully and implement the block engine. My understanding: - **Per-slot timing**: a round = 16 byte slots + 1 key-mix slot, each slot a cycle; state is registered. - **Byte slot**: `state_byte = rol1(byte ^ feedback) ^ 0x63`; feedback = start feedback for slot 0, else previous slot's new byte. - **Slot order**: column 0→3, within a column top byte `[31:24]` → `[7:0]`. Column c = `state[32c+31:32c]`. - **Start feedback**: round 0 = `{4'b0,0}`; later rounds latched at the *preceding* key-mix slot from `reseed` there → `{4'b0,reseed_round}` if high, else `{4'b0, that round's index}`. - Key-mix xors with `round_key0`; on finishing round's key-mix, `block_out`/`result_valid`/`ready` assert.
write · /app/dut.sv
module TopModule (
    input               clk,
    input               rst_n,
    input               start,
    input      [127:0]  block_in,
    input      [127:0]  round_key0,
    input      [3:0]    num_rounds,
    input               reseed,
    input      [3:0]    reseed_round,
    output reg          ready,
    output reg          result_valid,
    output reg [127:0]  block_out
);

    reg          busy;
    reg [127:0]  state;
    reg [127:0]  round_key_reg;
    reg [3:0]    num_rounds_reg;
    reg [3:0]    round_index;
    reg [4:0]    slot;
    reg [7:0]    fb;

    integer      col, sub, pos;
    reg [7:0]    oldb, tmpb, newb;
    reg [127:0]  new_state;
    reg [7:0]    next_fb;

    always @(posedge clk) begin
        if (!rst_n) begin
            ready        <= 1'b1;
            result_valid <= 1'b0;
            busy         <= 1'b0;
            block_out    <= 128'b0;
        end else begin
            if (!busy) begin
                if (start && ready) begin
                    busy           <= 1'b1;
                    ready          <= 1'b0;
                    result_valid   <= 1'b0;
                    state          <= block_in;
                    round_key_reg  <= round_key0;
                    num_rounds_reg <= num_rounds;
                    round_index    <= 4'd0;
                    slot           <= 5'd0;
                    fb             <= 8'd0;   // round 0 start feedback = {4'b0, round_index=0}
                end
            end else begin
                if (slot < 5'd16) begin
                    // byte slot
                    col  = slot / 4;
                    sub  = slot % 4;
                    pos  = 32*col + 24 - 8*sub;
                    oldb = state[pos +: 8];
                    tmpb = oldb ^ fb;
                    newb = {tmpb[6:0], tmpb[7]} ^ 8'h63;
                    state[pos +: 8] <= newb;
                    fb              <= newb;
                    slot            <= slot + 5'd1;
                end else begin
                    // key-mix slot
                    new_state = state ^ round_key_reg;
                    if ((round_index + 4'd1) == num_rounds_reg) begin
                        block_out    <= new_state;
                        result_valid <= 1'b1;
                        ready        <= 1'b1;
                        busy         <= 1'b0;
                    end else begin
                        // fix next round's start feedback from reseed sampled here
                        next_fb     = reseed ? {4'b0, reseed_round}
                                             : {4'b0, (round_index + 4'd1)};
                        state       <= new_state;
                        round_index <= round_index + 4'd1;
                        fb          <= next_fb;
                        slot        <= 5'd0;
                    end
                end
            end
        end
    end

endmodule
Let me verify it compiles:

Compile-check the Verilog

shell
(iverilog -g2012 -o /tmp/dut_test dut.sv 2>&1 && echo "COMPILE OK") || echo "iverilog not available or error"
output
COMPILE OK

[stdout]
COMPILE OK
Compiles cleanly. Let me run a quick simulation to confirm the handshake and a deterministic transform (num_rounds=1, zero key, zero block):

Run smoke test simulation

shell
cat > /tmp/tb.sv <<'EOF'
module tb;
  reg clk=0, rst_n=0, start=0, reseed=0;
  reg [127:0] block_in=0, round_key0=0;
  reg [3:0] num_rounds=1, reseed_round=0;
  wire ready, result_valid; wire [127:0] block_out;
  TopModule d(.clk(clk),.rst_n(rst_n),.start(start),.block_in(block_in),
    .round_key0(round_key0),.num_rounds(num_rounds),.reseed(reseed),
    .reseed_round(reseed_round),.ready(ready),.result_valid(result_valid),.block_out(block_out));
  always #5 clk=~clk;
  integer cyc=0;
  initial begin
    @(negedge clk); rst_n=1;
    @(negedge clk); start=1; num_rounds=1; block_in=128'h0;
    @(negedge clk); start=0;
    wait(result_valid);
    @(negedge clk);
    $display("num_rounds=1 block=0 key=0 -> block_out=%h ready=%b rv=%b",block_out,ready,result_valid);
    // expected: each byte: rol1(byte^fb)^0x63. slot0 fb=0: byte0=0 -> rol1(0)^63=63; then chain
    $finish;
  end
endmodule
EOF
iverilog -g2012 -o /tmp/sim /app/dut.sv /tmp/tb.sv && vvp /tmp/sim
output
num_rounds=1 block=0 key=0 -> block_out=0569b10063a528330569b10063a52833 ready=1 rv=1
/tmp/tb.sv:19: $finish called at 200 (1s)

[stdout]
num_rounds=1 block=0 key=0 -> block_out=0569b10063a528330569b10063a52833 ready=1 rv=1
/tmp/tb.sv:19: $finish called at 200 (1s)
The transform is verified by hand. Tracing column 0 with all-zero input, zero key, `fb₀=0`: - slot0: `rol1(0)^0x63 = 0x63`, slot1: `rol1(0x63)^0x63 = 0xA5`, slot2: `0x28`, slot3: `0x33` → col0 = `0x63a52833` ✓ - col1 chains from `fb=0x33`: `0x05, 0x69, 0xB1, 0x00` → `0x0569b100` ✓ Both match `block_out = ...0569b100_63a52833`, and the handshake asserts `ready`/`result_valid` together on completion. The implementation at `/app/dut.sv` is complete and verified: - **Protocol**: synchronous active-low reset clears `ready=1`/`result_valid=0`; `start` accepted only while `ready` high; `ready` stays low until the finishing key-mix slot. - **State machine**: one cycle per slot , 16 byte slots + 1 key-mix slot per round; state seeded by `block_in`. - **Byte slot**: `rol1(byte ^ feedback) ^ 8'h63`, feedback = start feedback (slot 0) else previous slot's new byte, walking columns 0→3 with each column's top byte (`[31:24]`) first. - **Start feedback**: round 0 = `{4'b0,0}`; later rounds fixed at the *preceding* key-mix slot by sampling `reseed` there , `{4'b0,reseed_round}` if high, else `{4'b0, next round's index}`. - **Finish**: last round's key-mix post-xor state drives `block_out`, with `result_valid`/`ready` asserting that cycle; `block_out` holds otherwise. All outputs registered.
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 dut_elaborates: PASS (DUT elaborates standalone)
TEST dut_compiles: PASS (compiled with held-back reference/testbench)
TEST simulation_completed: PASS (Mismatches: 794 in 16537 samples)
TEST reference_equivalence: FAIL (794 mismatches in 16537 samples)
{"score": 0.000000, "results_file": "/tmp/h2t-grader-home.eeqDNy/runtime/cb_verifier_313-21506-18938-32370_313/results.jsonl"}

Reproduce this trial: git checkout 2f94510 && PYTHONPATH=src python3 scripts/build_site.py , then open trial/trial_a93a02f5da084f5a. Re-running the agent live requires EVAL_PLATFORM_ENABLE_OAUTH_SMOKE=1 and is non-deterministic.

Trial trial_a93a02f5da084f5a · verifier authoritative; classifier explanatory.