SyncVals · Trajectory

dualmaster-membridge

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

EvidenceVerifier output: "TEST reference_equivalence: PASS (all 3839 samples matched reference)" and "Mismatches: 0 in 3839 samples". The trajectory shows the agent derived the FSM from the instruction, then wrote /app/dut.sv with states for E+1 memory request, E+3 data capture, E+4 ack, and warm/cold arbitration; no evidence of reading tests/ or solution/.

Root causeThe agent correctly implemented the specified two-requester read-only memory bridge timing and arbitration behavior. The tests verify behavioral equivalence against a reference module across single-request, concurrent, reset, warm/fairness, and randomized scenarios, which is aligned with the instruction.

RecommendationN/A - task is fine

Trajectory

Tool-by-tool agent trajectory

3 tool calls · 2 tool types · 8 steps

A bridge shares one read-only memory port between requesters A and B, keeping neither starved. Ports: clk, rst, a_req_i, a_addr_i (8), a_ack_o, a_data_o (16), b_req_i, b_addr_i (8), b_ack_o, b_data_o (16), m_req_o, m_addr_o (8), m_data_i (16). rst is synchronous active high, clearing all state and outputs to 0. All outputs are registered. A requester holds req and addr stable through the cycle after its ack. The bridge samples on the idle edge after a request first appears, calling that edge E; a freshly-arriving request is registered one idle cycle before it is sampled as E. One request finishes before the next is sampled. m_req_o and m_addr_o carry the chosen command during E+1 only. m_data_i is valid during E+3. The winner's ack and word are high during E+4 only, the other ack 0. E+4 is the last occupied cycle; the bridge is idle again at E+5, never earlier or later. A sample after a fully idle stretch favours A when both ask. The sample at E+5 directly after an operation instead takes the requester that did not just win if it asks, else the one that did; a later idle stretch resets this, so the next cold sample favours A again. edge E E+1 E+3 E+4 E+5 E+6 m_req_o 0 1 0 0 0 1 a_ack_o 0 0 0 1 0 0 a_data_o and b_data_o matter only while the matching ack is high. Write module TopModule to /app/dut.sv. Plain ASCII synthesizable SystemVerilog only: no define, include, ifdef, system tasks, force, release, bind.

I'll analyze the timing spec carefully, then write the module. My reading of the pipeline (cycle labels match the table): - **E**: idle cycle, a request is registered/pending → decision happens at this edge - **E+1**: `m_req_o=1`, `m_addr_o`=winner's addr (command to memory) - **E+2**: waiting (`m_req_o=0`) - **E+3**: `m_data_i` valid → captured at this edge - **E+4**: winner's `ack`/`data` high (only cycle) - **E+5**: idle again; if a request is pending this is the *warm* sample edge → next command at **E+6** Arbitration: cold sample (after idle stretch) → A wins ties; warm sample (at E+5) → prefer the requester that did *not* just win, else the one that did; an idle-empty cycle clears the warm flag. Let me verify the fairness/alternation and the exact table against this FSM before committing, then write it.

write · /app/dut.sv

module TopModule (
    input  logic        clk,
    input  logic        rst,
    input  logic        a_req_i,
    input  logic [7:0]  a_addr_i,
    output logic        a_ack_o,
    output logic [15:0] a_data_o,
    input  logic        b_req_i,
    input  logic [7:0]  b_addr_i,
    output logic        b_ack_o,
    output logic [15:0] b_data_o,
    output logic        m_req_o,
    output logic [7:0]  m_addr_o,
    input  logic [15:0] m_data_i
);

    // Busy-sequence states (cycle labels relative to sampling edge E)
    localparam logic [2:0] S_IDLE = 3'd0; // idle: decision made at this edge
    localparam logic [2:0] S_REQ  = 3'd1; // E+1: command on memory port
    localparam logic [2:0] S_W1   = 3'd2; // E+2: waiting
    localparam logic [2:0] S_W2   = 3'd3; // E+3: m_data_i valid, capture at edge
    localparam logic [2:0] S_ACK  = 3'd4; // E+4: winner ack/data high

    logic [2:0] st;
    logic       warm;      // 1 => sampling directly after an operation
    logic       win;       // 0 = A, 1 = B : current/last winner

    // Requests/addresses are registered one idle cycle before being sampled.
    logic       a_req_r, b_req_r;
    logic [7:0] a_addr_r, b_addr_r;

    // Combinational arbitration decision.
    logic       start_op;
    logic       sel_win;

    always_comb begin
        start_op = a_req_r | b_req_r;
        if (warm) begin
            // Prefer the requester that did NOT just win; else the one that did.
            if (win == 1'b0)
                sel_win = b_req_r ? 1'b1 : 1'b0; // A just won -> favour B
            else
                sel_win = a_req_r ? 1'b0 : 1'b1; // B just won -> favour A
        end else begin
            // Cold sample after an idle stretch: A wins ties.
            sel_win = a_req_r ? 1'b0 : 1'b1;
        end
    end

    always_ff @(posedge clk) begin
        if (rst) begin
            st       <= S_IDLE;
            warm     <= 1'b0;
            win      <= 1'b0;
            a_req_r  <= 1'b0;
            b_req_r  <= 1'b0;
            a_addr_r <= 8'd0;
            b_addr_r <= 8'd0;
            m_req_o  <= 1'b0;
            m_addr_o <= 8'd0;
            a_ack_o  <= 1'b0;
            b_ack_o  <= 1'b0;
            a_data_o <= 16'd0;
            b_data_o <= 16'd0;
        end else begin
            // Register the incoming requests/addresses each cycle.
            a_req_r  <= a_req_i;
            b_req_r  <= b_req_i;
            a_addr_r <= a_addr_i;
            b_addr_r <= b_addr_i;

            // Default single-cycle outputs.
            m_req_o  <= 1'b0;
            a_ack_o  <= 1'b0;
            b_ack_o  <= 1'b0;

            case (st)
                S_IDLE: begin
                    if (start_op) begin
                        win      <= sel_win;
                        m_addr_o <= sel_win ? b_addr_r : a_addr_r;
                        m_req_o  <= 1'b1;          // command appears next cycle (E+1)
                        st       <= S_REQ;
                    end else begin
                        warm <= 1'b0;              // idle stretch resets to cold
                        st   <= S_IDLE;
                    end
                end
                S_REQ: st <= S_W1;
                S_W1:  st <= S_W2;
                S_W2: begin
                    // m_data_i valid during E+3: capture and raise ack for E+4.
                    if (win == 1'b0) begin
                        a_data_o <= m_data_i;
                        a_ack_o  <= 1'b1;
                    end else begin
                        b_data_o <= m_data_i;
                        b_ack_o  <= 1'b1;
                    end
                    st <= S_ACK;
                end
                S_ACK: begin
                    warm <= 1'b1;                  // next sample (E+5) is warm
                    st   <= S_IDLE;
                end
                default: st <= S_IDLE;
            endcase
        end
    end
endmodule

Let me sanity-check that it compiles.

shell

(verilator --lint-only -Wall dut.sv 2>&1 | head -30) || echo "verilator not available"; echo "---"; (iverilog -g2012 -o /tmp/d.out dut.sv 2>&1 | head -30 && echo "iverilog OK") || echo "iverilog failed/unavailable"

output

/bin/bash: line 1: verilator: command not found
---
iverilog OK

[stdout]
/bin/bash: line 1: verilator: command not found
---
iverilog OK

Compiles cleanly. Let me verify behavior with a quick testbench covering the exact table (cold single-A) plus the fairness alternation and warm/cold reset.

shell

cat > /tmp/tb.sv <<'EOF'
module tb;
  logic clk=0, rst;
  logic a_req_i, b_req_i;
  logic [7:0] a_addr_i, b_addr_i, m_addr_o;
  logic a_ack_o, b_ack_o, m_req_o;
  logic [15:0] a_data_o, b_data_o, m_data_i;

  TopModule dut(.clk,.rst,.a_req_i,.a_addr_i,.a_ack_o,.a_data_o,
    .b_req_i,.b_addr_i,.b_ack_o,.b_data_o,.m_req_o,.m_addr_o,.m_data_i);

  always #5 clk=~clk;

  // Fake memory: data valid 2 cycles after m_req_o high (addr+16'h1000)
  logic [15:0] pipe1, pipe2;
  always @(posedge clk) begin
    pipe1 <= m_req_o ? {8'h10, m_addr_o} : 16'hxxxx;
    pipe2 <= pipe1;
  end
  assign m_data_i = pipe2;

  integer cyc=0;
  always @(posedge clk) cyc<=cyc+1;

  initial begin
    rst=1; a_req_i=0; b_req_i=0; a_addr_i=8'hA5; b_addr_i=8'hB7;
    @(posedge clk); #1 rst=0;
    // cold single A
    a_req_i=1;
    repeat(20) begin
      @(posedge clk);
      #1 $display("cyc=%0d st? m_req=%b m_addr=%02h a_ack=%b a_data=%04h b_ack=%b b_data=%04h",
          cyc, m_req_o, m_addr_o, a_ack_o, a_data_o, b_ack_o, b_data_o);
    end
    a_req_i=0;
    $display("---- both continuous (fairness) ----");
    @(posedge clk); #1 b_req_i=0;
    // idle stretch to reset to cold
    repeat(3) @(posedge clk);
    a_req_i=1; b_req_i=1;
    repeat(30) begin
      @(posedge clk);
      #1 if(a_ack_o||b_ack_o||m_req_o)
         $display("cyc=%0d m_req=%b m_addr=%02h a_ack=%b b_ack=%b", cyc,m_req_o,m_addr_o,a_ack_o,b_ack_o);
    end
    $finish;
  end
endmodule
EOF
iverilog -g2012 -o /tmp/d.out /tmp/tb.sv /app/dut.sv && vvp /tmp/d.out

output

cyc=2 st? m_req=0 m_addr=00 a_ack=0 a_data=0000 b_ack=0 b_data=0000
cyc=3 st? m_req=1 m_addr=a5 a_ack=0 a_data=0000 b_ack=0 b_data=0000
cyc=4 st? m_req=0 m_addr=a5 a_ack=0 a_data=0000 b_ack=0 b_data=0000
cyc=5 st? m_req=0 m_addr=a5 a_ack=0 a_data=0000 b_ack=0 b_data=0000
cyc=6 st? m_req=0 m_addr=a5 a_ack=1 a_data=10a5 b_ack=0 b_data=0000
cyc=7 st? m_req=0 m_addr=a5 a_ack=0 a_data=10a5 b_ack=0 b_data=0000
cyc=8 st? m_req=1 m_addr=a5 a_ack=0 a_data=10a5 b_ack=0 b_data=0000
cyc=9 st? m_req=0 m_addr=a5 a_ack=0 a_data=10a5 b_ack=0 b_data=0000
cyc=10 st? m_req=0 m_addr=a5 a_ack=0 a_data=10a5 b_ack=0 b_data=0000
cyc=11 st? m_req=0 m_addr=a5 a_ack=1 a_data=10a5 b_ack=0 b_data=0000
cyc=12 st? m_req=0 m_addr=a5 a_ack=0 a_data=10a5 b_ack=0 b_data=0000
cyc=13 st? m_req=1 m_addr=a5 a_ack=0 a_data=10a5 b_ack=0 b_data=0000
cyc=14 st? m_req=0 m_addr=a5 a_ack=0 a_data=10a5 b_ack=0 b_data=0000
cyc=15 st? m_req=0 m_addr=a5 a_ack=0 a_data=10a5 b_ack=0 b_data=0000
cyc=16 st? m_req=0 m_addr=a5 a_ack=1 a_data=10a5 b_ack=0 b_data=0000
cyc=17 st? m_req=0 m_addr=a5 a_ack=0 a_data=10a5 b_ack=0 b_data=0000
cyc=18 st? m_req=1 m_addr=a5 a_ack=0 a_data=10a5 b_ack=0 b_data=0000
cyc=19 st? m_req=0 m_addr=a5 a_ack=0 a_data=10a5 b_ack=0 b_data=0000
cyc=20 st? m_req=0 m_addr=a5 a_ack=0 a_data=10a5 b_ack=0 b_data=0000
cyc=21 st? m_req=0 m_addr=a5 a_ack=1 a_data=10a5 b_ack=0 b_data=0000
---- both continuous (fairness) ----
cyc=26 m_req=1 m_addr=a5 a_ack=0 b_ack=0
cyc=29 m_req=0 m_addr=a5 a_ack=1 b_ack=0
cyc=31 m_req=1 m_addr=b7 a_ack=0 b_ack=0
cyc=34 m_req=0 m_addr=b7 a_ack=0 b_ack=1
cyc=36 m_req=1 m_addr=a5 a_ack=0 b_ack=0
cyc=39 m_req=0 m_addr=a5 a_ack=1 b_ack=0
cyc=41 m_req=1 m_addr=b7 a_ack=0 b_ack=0
cyc=44 m_req=0 m_addr=b7 a_ack=0 b_ack=1
cyc=46 m_req=1 m_addr=a5 a_ack=0 b_ack=0
cyc=49 m_req=0 m_addr=a5 a_ack=1 b_ack=0
cyc=51 m_req=1 m_addr=b7 a_ack=0 b_ack=0
cyc=54 m_req=0 m_addr=b7 a_ack=0 b_ack=1
/tmp/tb.sv:45: $finish called at 546 (1s)

[stdout]
cyc=2 st? m_req=0 m_addr=00 a_ack=0 a_data=0000 b_ack=0 b_data=0000
cyc=3 st? m_req=1 m_addr=a5 a_ack=0 a_data=0000 b_ack=0 b_data=0000
cyc=4 st? m_req=0 m_addr=a5 a_ack=0 a_data=0000 b_ack=0 b_data=0000
cyc=5 st? m_req=0 m_addr=a5 a_ack=0 a_data=0000 b_ack=0 b_data=0000
cyc=6 st? m_req=0 m_addr=a5 a_ack=1 a_data=10a5 b_ack=0 b_data=0000
cyc=7 st? m_req=0 m_addr=a5 a_ack=0 a_data=10a5 b_ack=0 b_data=0000
cyc=8 st? m_req=1 m_addr=a5 a_ack=0 a_data=10a5 b_ack=0 b_data=0000
cyc=9 st? m_req=0 m_addr=a5 a_ack=0 a_data=10a5 b_ack=0 b_data=0000
cyc=10 st? m_req=0 m_addr=a5 a_ack=0 a_data=10a5 b_ack=0 b_data=0000
cyc=11 st? m_req=0 m_addr=a5 a_ack=1 a_data=10a5 b_ack=0 b_data=0000
cyc=12 st? m_req=0 m_addr=a5 a_ack=0 a_data=10a5 b_ack=0 b_data=0000
cyc=13 st? m_req=1 m_addr=a5 a_ack=0 a_data=10a5 b_ack=0 b_data=0000
cyc=14 st? m_req=0 m_addr=a5 a_ack=0 a_data=10a5 b_ack=0 b_data=0000
cyc=15 st? m_req=0 m_addr=a5 a_ack=0 a_data=10a5 b_ack=0 b_data=0000
cyc=16 st? m_req=0 m_addr=a5 a_ack=1 a_data=10a5 b_ack=0 b_data=0000
cyc=17 st? m_req=0 m_addr=a5 a_ack=0 a_data=10a5 b_ack=0 b_data=0000
cyc=18 st? m_req=1 m_addr=a5 a_ack=0 a_data=10a5 b_ack=0 b_data=0000
cyc=19 st? m_req=0 m_addr=a5 a_ack=0 a_data=10a5 b_ack=0 b_data=0000
cyc=20 st? m_req=0 m_addr=a5 a_ack=0 a_data=10a5 b_ack=0 b_data=0000
cyc=21 st? m_req=0 m_addr=a5 a_ack=1 a_data=10a5 b_ack=0 b_data=0000
---- both continuous (fairness) ----
cyc=26 m_req=1 m_addr=a5 a_ack=0 b_ack=0
cyc=29 m_req=0 m_addr=a5 a_ack=1 b_ack=0
cyc=31 m_req=1 m_addr=b7 a_ack=0 b_ack=0
cyc=34 m_req=0 m_addr=b7 a_ack=0 b_ack=1
cyc=36 m_req=1 m_addr=a5 a_ack=0 b_ack=0
cyc=39 m_req=0 m_addr=a5 a_ack=1 b_ack=0
cyc=41 m_req=1 m_addr=b7 a_ack=0 b_ack=0
cyc=44 m_req=0 m_addr=b7 a_ack=0 b_ack=1
cyc=46 m_req=1 m_addr=a5 a_ack=0 b_ack=0
cyc=49 m_req=0 m_addr=a5 a_ack=1 b_ack=0
cyc=51 m_req=1 m_addr=b7 a_ack=0 b_ack=0
cyc=54 m_req=0 m_addr=b7 a_ack=0 b_ack=1
/tmp/tb.sv:45: $finish called at 546 (1s)

Everything matches the spec exactly. **Cold single-A trace** (E=cyc2): `m_req_o` = 0,1,0,0,0,1 across E, E+1, E+3, E+4, E+5, E+6, and `a_ack_o` = 0,0,0,1,0,0 , the ack + data (`10a5`) land only at E+4, memory command only at E+1, idle at E+5. Exactly the given table. **Fairness**: cold start favors A (addr `a5` first), then acks alternate A→B→A→B… perfectly , neither starved. The idle stretch between test phases correctly reset the arbiter back to cold (A favored again). The module in `/app/dut.sv`: - Registers requests/addresses one idle cycle before sampling (edge E). - Fully registered outputs, synchronous active-high reset clearing all state/outputs. - FSM sequence IDLE→REQ(E+1)→W1(E+2)→W2(E+3, capture `m_data_i`)→ACK(E+4)→IDLE(E+5), with the E+5 idle cycle acting as the next sampling edge. - Cold arbitration favors A on ties; warm arbitration (a `warm` flag set on completion) prefers the non-winner, else the winner; an idle-empty cycle clears `warm`, so the next cold sample favors A again. Plain ASCII synthesizable SystemVerilog , no `define`/`include`/`ifdef`/system tasks/`force`/`release`/`bind`. Compiles clean under `iverilog -g2012`.

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_compiles: PASS (compiled with held-back reference/testbench)
TEST simulation_completed: PASS (Mismatches: 0 in 3839 samples)
TEST reference_equivalence: PASS (all 3839 samples matched reference)
{"score": 1.000000, "results_file": "/tmp/h2t-grader-home.0lAS1o/runtime/cb_verifier_316-27753-31840-8302_316/results.jsonl"}

Reproduce this trial: git checkout 2f94510 && PYTHONPATH=src python3 scripts/build_site.py , then open trial/trial_76e4924225174259. Re-running the agent live requires EVAL_PLATFORM_ENABLE_OAUTH_SMOKE=1 and is non-deterministic.

Trial trial_76e4924225174259 · verifier authoritative; classifier explanatory.