SyncVals · Trajectory

stream-frame-hold

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 output: "TEST reference_equivalence: FAIL (29 mismatches in 258 samples)" and "simulation_completed: PASS". The agent wrote /app/dut.sv directly and stopped without testing. Its implementation differs from the reference behavior, e.g. in the xfer branch it only does `m_tvalid_o <= 1'b0;` and conditionally starts pads, while the reference also clears `m_tlast_o <= 1'b0;` and uses a separate `in_pad/pending_pad` state machine. The task instruction explicitly specified the required FIFO depth, registered AXI-stream timing, padding behavior, and simultaneous push/load occupancy handling.

Root causeThe task is well-specified and the tests check the described cycle-level behavior against a reference model. The failure came from the agent producing an imperfect RTL implementation and not validating/debugging it before stopping.

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, wr_i, wr_data[31:0], wr_last_i, wr_ready_o, m_tvalid_o, m_tdata_o[31:0], m_tlast_o, and m_tready_i. rst is synchronous active high and clears the FIFO and all outputs. The block buffers 32-bit write beats into a depth-8 FIFO and emits them in order on an AXI4-Stream master interface. Assert wr_ready_o when the FIFO is not full. On a rising edge with wr_i=1 and wr_ready_o=1, push wr_data and its wr_last_i flag. If that same edge also loads a payload onto the stream, update occupancy once for both events so the write is not lost. Drive m_tvalid_o, m_tdata_o, and m_tlast_o from registers, not combinationally. Let xfer = m_tvalid_o && m_tready_i. On an xfer edge, deassert m_tvalid_o; load the next beat only on a later edge where m_tvalid_o is already low, then assert it. So one idle cycle separates consecutive accepted beats, and m_tdata_o holds during idle. While m_tready_i=0, hold the beat unchanged. Payload beats always drive m_tlast_o=0. After a payload written with wr_last_i=1 is accepted, emit exactly 2 pad beats before the next FIFO beat. Pad data is last_payload ^ 32'h0BAD_F00D, where last_payload is that payload's data. Pads follow the same one-idle-cycle registered discipline. m_tlast_o=1 only on the second pad. Use plain ASCII. No system tasks, preprocessor directives, DPI, force/release, or hidden grader identifiers.

write · /app/dut.sv

module TopModule (
    input  wire        clk,
    input  wire        rst,
    input  wire        wr_i,
    input  wire [31:0] wr_data,
    input  wire        wr_last_i,
    output wire        wr_ready_o,
    output reg         m_tvalid_o,
    output reg  [31:0] m_tdata_o,
    output reg         m_tlast_o,
    input  wire        m_tready_i
);

    // Depth-8 FIFO storing {last, data}
    reg [32:0] fifo_mem [0:7];
    reg  [2:0] wptr;
    reg  [2:0] rptr;
    reg  [3:0] count;

    wire full  = (count == 4'd8);
    wire empty = (count == 4'd0);

    assign wr_ready_o = !full;

    // Metadata for the currently loaded output beat
    reg        beat_is_last_payload; // current beat is a payload with wr_last=1
    reg  [1:0] pad_pending;          // remaining pad beats to emit (0,1,2)
    reg [31:0] last_payload;         // data of the last accepted last-payload

    always @(posedge clk) begin
        if (rst) begin
            m_tvalid_o           <= 1'b0;
            m_tdata_o            <= 32'd0;
            m_tlast_o            <= 1'b0;
            beat_is_last_payload <= 1'b0;
            pad_pending          <= 2'd0;
            last_payload         <= 32'd0;
            wptr                 <= 3'd0;
            rptr                 <= 3'd0;
            count                <= 4'd0;
        end else begin
            reg do_push;
            reg do_pop;

            do_push = wr_i && !full;
            do_pop  = 1'b0;

            // ---- Output loading (registered) ----
            if (m_tvalid_o && m_tready_i) begin
                // xfer edge: deassert valid, hold data/last
                m_tvalid_o <= 1'b0;
                if (beat_is_last_payload) begin
                    pad_pending  <= 2'd2;
                    last_payload <= m_tdata_o;
                end
            end else if (!m_tvalid_o) begin
                // idle: load next beat if available
                if (pad_pending != 2'd0) begin
                    m_tdata_o            <= last_payload ^ 32'h0BADF00D;
                    m_tlast_o            <= (pad_pending == 2'd1);
                    m_tvalid_o           <= 1'b1;
                    beat_is_last_payload <= 1'b0;
                    pad_pending          <= pad_pending - 2'd1;
                end else if (!empty) begin
                    m_tdata_o            <= fifo_mem[rptr][31:0];
                    m_tlast_o            <= 1'b0;
                    m_tvalid_o           <= 1'b1;
                    beat_is_last_payload <= fifo_mem[rptr][32];
                    rptr                 <= rptr + 3'd1;
                    do_pop               = 1'b1;
                end
            end

            // ---- FIFO push ----
            if (do_push) begin
                fifo_mem[wptr] <= {wr_last_i, wr_data};
                wptr           <= wptr + 3'd1;
            end

            // ---- Single occupancy update for both events ----
            count <= count + (do_push ? 4'd1 : 4'd0) - (do_pop ? 4'd1 : 4'd0);
        end
    end

endmodule

I've written `/app/dut.sv`. Here's how it maps to the spec: **FIFO (depth-8):** `fifo_mem` stores `{wr_last_i, wr_data}` (33 bits). `wr_ready_o = !full` combinationally. Push happens on `wr_i && !full`; occupancy is updated **once** at the end (`count + push - pop`), so a simultaneous push+pop never drops the write. **Registered stream outputs:** `m_tvalid_o/m_tdata_o/m_tlast_o` are all driven from registers. **One-idle-cycle discipline:** - On an `xfer` edge (`m_tvalid_o && m_tready_i`), valid deasserts and data/last hold. - A new beat loads only in the branch guarded by `!m_tvalid_o` (valid already low), which forces exactly one idle cycle between accepted beats. - When `m_tready_i=0` with valid high, neither branch fires, so the beat holds unchanged. **Pad sequence:** When a beat whose stored `last` flag is 1 is accepted, `pad_pending<=2` and `last_payload<=m_tdata_o`. While `pad_pending!=0`, loads are pad beats (priority over FIFO), data = `last_payload ^ 32'h0BADF00D`, with `m_tlast_o=1` only when `pad_pending==1` (the second pad). Payload beats always drive `m_tlast_o=0`. Pads use the same idle-cycle load path. **Reset:** synchronous, active-high, clears FIFO pointers/count and all output/state registers.

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_standalone: PASS (DUT elaborates standalone)
TEST harness_prepare: PASS (harness names nonce-renamed)
TEST dut_compiles: PASS (compiled with held-back reference/testbench)
TEST simulation_completed: PASS (Mismatches: 29 in 258 samples)
TEST reference_equivalence: FAIL (29 mismatches in 258 samples)

Reproduce this trial: git checkout 2f94510 && PYTHONPATH=src python3 scripts/build_site.py , then open trial/trial_6f27e0801db8425a. Re-running the agent live requires EVAL_PLATFORM_ENABLE_OAUTH_SMOKE=1 and is non-deterministic.

Trial trial_6f27e0801db8425a · verifier authoritative; classifier explanatory.