SyncVals · Trajectory

bus-slave-abort-ack

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

EvidenceInstruction specified the full bus transducer behavior including E/E+1/E+2/E+3 timing, mix(a,x), dropped responses, read/write collision priority, and forbidden constructs. Tests performed hidden reference equivalence: `TEST reference_equivalence: PASS (all 5367 samples matched reference)`. Agent trajectory shows it wrote `/app/dut.sv` with a real four-slot implementation using `slot`, `primed`, read/write pipelines, `mix`, `acc = cyc_i & stb_i & ~stall_o`, and ran its own sanity benches; no evidence of reading `/tests`, `ref.sv`, or `solution`.

Root causeThe agent legitimately implemented the specified RTL behavior and passed a behavioral reference-equivalence verifier. The tests align with the instruction and check functional behavior rather than superficial implementation details.

RecommendationN/A - task is fine

Trajectory

Tool-by-tool agent trajectory

4 tool calls · 2 tool types · 10 steps

Write /app/dut.sv defining TopModule, a four-slot registered bus transducer. Ports are clk, rst, cyc_i, stb_i, we_i, adr_i[1:0], dat_i[15:0], stall_o, ack_o, dat_o[15:0]. rst synchronously clears slots, primed bits, pending work, and outputs. Edge E is the accept posedge; E+1 is the next posedge. Observe timing after the named posedge. Accept a request at E when cyc_i and stb_i are high and pre-edge stall_o is low. Lane k of a word is bits k,k+4,k+8,k+12 in increasing bit order. Function mix(a,x) packs, into lane k, the bit-reversed source lane (k+a) mod 4. Read accepted at E captures slot adr_i and its primed bit. Its E+2 response drives dat_o=0 if unprimed, else mix(adr_i,captured). Write accepted at E commits at E+3: old_slot is the pre-edge slot value, slot adr_i becomes mix(adr_i,old_slot) xor dat_i, and primed sets. Its E+3 response returns the committed slot. ack_o pulses only when cyc_i is high at the response edge. If cyc_i is low there, ack_o/dat_o are 0; dropped responses vanish, and dropped writes still commit. If read/write responses share an edge, read data wins and the write still commits. For an accepted write, stall_o is high only after E+1 and E+2. ack_o/dat_o are 0 outside active response edges. Submit synthesizable ASCII Verilog. The verifier rejects system tasks/functions, directives, force/release/deassign/bind/alias, supply/pull/tran nets, verifier names, and identifiers ending _ref or _dut.

Looking at this problem, I need to design a registered pipelined bus transducer. Let me work through the timing carefully and write the module.

write · /app/dut.sv

module TopModule(
  input clk,
  input rst,
  input cyc_i,
  input stb_i,
  input we_i,
  input [1:0] adr_i,
  input [15:0] dat_i,
  output reg stall_o,
  output reg ack_o,
  output reg [15:0] dat_o
);

  // Storage: four 16-bit slots and their primed bits
  reg [15:0] slot [0:3];
  reg        primed [0:3];

  // Read pipeline: accepted at E -> responds at E+2 (2 stages deep)
  reg        rA_v, rB_v;
  reg [15:0] rA_d, rB_d;

  // Write pipeline: accepted at E -> commits/responds at E+3 (3 stages deep)
  reg        wA_v, wB_v, wC_v;
  reg [1:0]  wA_a, wB_a, wC_a;
  reg [15:0] wA_d, wB_d, wC_d;

  // Combinational temporaries
  reg        acc;
  reg [15:0] wnew_v;
  reg [15:0] rcap_v;

  // mix(a,x): into lane k place the bit-reversed source lane (k+a) mod 4.
  // Lane j of a word is bits j, j+4, j+8, j+12 in increasing bit order.
  function [15:0] mix;
    input [1:0]  a;
    input [15:0] x;
    integer k;
    integer s;
    begin
      mix = 16'b0;
      for (k = 0; k < 4; k = k + 1) begin
        s = (k + a) & 3;          // source lane index (mod 4)
        // source lane bits (increasing): x[s], x[s+4], x[s+8], x[s+12]
        // bit-reversed into destination lane k (increasing)
        mix[k]      = x[s+12];
        mix[k+4]    = x[s+8];
        mix[k+8]    = x[s+4];
        mix[k+12]   = x[s];
      end
    end
  endfunction

  always @(posedge clk) begin
    if (rst) begin
      slot[0] <= 16'b0; slot[1] <= 16'b0; slot[2] <= 16'b0; slot[3] <= 16'b0;
      primed[0] <= 1'b0; primed[1] <= 1'b0; primed[2] <= 1'b0; primed[3] <= 1'b0;
      rA_v <= 1'b0; rB_v <= 1'b0; rA_d <= 16'b0; rB_d <= 16'b0;
      wA_v <= 1'b0; wB_v <= 1'b0; wC_v <= 1'b0;
      wA_a <= 2'b0; wB_a <= 2'b0; wC_a <= 2'b0;
      wA_d <= 16'b0; wB_d <= 16'b0; wC_d <= 16'b0;
      stall_o <= 1'b0; ack_o <= 1'b0; dat_o <= 16'b0;
    end else begin
      // Accept decision uses pre-edge stall_o
      acc = cyc_i & stb_i & ~stall_o;

      // Read capture (pre-edge slot/primed values)
      if (primed[adr_i]) rcap_v = mix(adr_i, slot[adr_i]);
      else               rcap_v = 16'b0;

      // Write commit value using pre-edge slot value at this (commit) edge
      wnew_v = mix(wC_a, slot[wC_a]) ^ wC_d;

      // ---- Response outputs (read wins on a shared edge) ----
      if (rB_v) begin
        dat_o <= cyc_i ? rB_d   : 16'b0;
        ack_o <= cyc_i ? 1'b1   : 1'b0;
      end else if (wC_v) begin
        dat_o <= cyc_i ? wnew_v : 16'b0;
        ack_o <= cyc_i ? 1'b1   : 1'b0;
      end else begin
        dat_o <= 16'b0;
        ack_o <= 1'b0;
      end

      // ---- Write commit (always happens if a write reaches this edge) ----
      if (wC_v) begin
        slot[wC_a]   <= wnew_v;
        primed[wC_a] <= 1'b1;
      end

      // ---- Read pipeline shift ----
      rB_v <= rA_v;
      rB_d <= rA_d;
      rA_v <= acc & ~we_i;
      rA_d <= rcap_v;

      // ---- Write pipeline shift ----
      wC_v <= wB_v; wC_a <= wB_a; wC_d <= wB_d;
      wB_v <= wA_v; wB_a <= wA_a; wB_d <= wA_d;
      wA_v <= acc & we_i; wA_a <= adr_i; wA_d <= dat_i;

      // ---- Stall: high only after E+1 and E+2 of an accepted write.
      // post-edge stall = (post wB_v | post wC_v) = (pre wA_v | pre wB_v)
      stall_o <= wA_v | wB_v;
    end
  end

endmodule

Let me verify it compiles with a simulator if available.

Compile/lint the Verilog

shell

(iverilog -g2012 -o /tmp/dut.out dut.sv 2>&1 && echo "IVERILOG OK") || (verilator --lint-only -Wno-lint dut.sv 2>&1 && echo "VERILATOR OK") || echo "no simulator available"

output

IVERILOG OK

[stdout]
IVERILOG OK

Compiles. Let me write a quick testbench to sanity-check the core timing and data behavior.

Run sanity testbench

shell

cat > /tmp/tb.sv << 'EOF'
module tb;
  reg clk=0, rst, cyc_i, stb_i, we_i;
  reg [1:0] adr_i; reg [15:0] dat_i;
  wire stall_o, ack_o; wire [15:0] dat_o;
  TopModule d(.clk(clk),.rst(rst),.cyc_i(cyc_i),.stb_i(stb_i),.we_i(we_i),
              .adr_i(adr_i),.dat_i(dat_i),.stall_o(stall_o),.ack_o(ack_o),.dat_o(dat_o));
  always #5 clk=~clk;

  // reference mix
  function [15:0] mix; input [1:0] a; input [15:0] x; integer k,s; begin
    mix=0; for(k=0;k<4;k=k+1) begin s=(k+a)&3;
      mix[k]=x[s+12]; mix[k+4]=x[s+8]; mix[k+8]=x[s+4]; mix[k+12]=x[s]; end end
  endfunction

  task step; begin @(posedge clk); #1; end endtask

  initial begin
    rst=1; cyc_i=0; stb_i=0; we_i=0; adr_i=0; dat_i=0;
    step; step; rst=0; step;
    // Write slot0 = D=16'h1234 (old=0 -> new = mix(0,0)^D = D)
    cyc_i=1; stb_i=1; we_i=1; adr_i=0; dat_i=16'h1234;
    @(posedge clk); #1;  // E accepted
    $display("after E: stall=%b ack=%b dat=%h",stall_o,ack_o,dat_o);
    cyc_i=1; stb_i=1; we_i=0; adr_i=0; // hold high; stall gating decides
    @(posedge clk); #1; $display("after E+1: stall=%b ack=%b dat=%h",stall_o,ack_o,dat_o);
    @(posedge clk); #1; $display("after E+2: stall=%b ack=%b dat=%h",stall_o,ack_o,dat_o);
    @(posedge clk); #1; $display("after E+3: stall=%b ack=%b dat=%h  (expect write resp=1234, ack=1)",stall_o,ack_o,dat_o);
    // now idle a bit then read slot0
    cyc_i=0; stb_i=0; @(posedge clk);#1;@(posedge clk);#1;
    cyc_i=1; stb_i=1; we_i=0; adr_i=0; dat_i=0;
    @(posedge clk);#1;  // read E
    cyc_i=1;stb_i=0;
    @(posedge clk);#1;  // E+1
    @(posedge clk);#1;  // E+2 read resp
    $display("read resp: ack=%b dat=%h (expect mix(0,1234)=%h)",ack_o,dat_o,mix(0,16'h1234));
    $finish;
  end
endmodule
EOF
iverilog -g2012 -o /tmp/t.out /tmp/dut_all.sv 2>/dev/null; iverilog -g2012 -o /tmp/t.out /app/dut.sv /tmp/tb.sv && vvp /tmp/t.out

output

after E: stall=0 ack=0 dat=0000
after E+1: stall=1 ack=0 dat=0000
after E+2: stall=1 ack=0 dat=0000
after E+3: stall=0 ack=1 dat=0000  (expect write resp=1234, ack=1)
read resp: ack=1 dat=4321 (expect mix(0,1234)=4321)
/tmp/tb.sv:36: $finish called at 116 (1s)

[stdout]
after E: stall=0 ack=0 dat=0000
after E+1: stall=1 ack=0 dat=0000
after E+2: stall=1 ack=0 dat=0000
after E+3: stall=0 ack=1 dat=0000  (expect write resp=1234, ack=1)
read resp: ack=1 dat=4321 (expect mix(0,1234)=4321)
/tmp/tb.sv:36: $finish called at 116 (1s)

The design works correctly. Note: at E+1 I accidentally held cyc/stb high with we=0, which accepted a **read** at E+1 (stall was low after E) , that read collides with the write response at E+3, and per spec **read wins** (data=0 since slot still unprimed at capture), while the **write still commits** (proven by the later read returning `4321 = mix(0,0x1234)`). Let me confirm the clean no-collision write response:

Verify clean write response and dropped-write commit

shell

cat > /tmp/tb2.sv << 'EOF'
module tb;
  reg clk=0, rst, cyc_i, stb_i, we_i; reg [1:0] adr_i; reg [15:0] dat_i;
  wire stall_o, ack_o; wire [15:0] dat_o;
  TopModule d(.clk(clk),.rst(rst),.cyc_i(cyc_i),.stb_i(stb_i),.we_i(we_i),
              .adr_i(adr_i),.dat_i(dat_i),.stall_o(stall_o),.ack_o(ack_o),.dat_o(dat_o));
  always #5 clk=~clk;
  initial begin
    rst=1;cyc_i=0;stb_i=0;we_i=0;adr_i=0;dat_i=0;
    @(posedge clk);@(posedge clk);#1;rst=0;@(posedge clk);#1;
    // clean write, then drop stb (keep cyc high for ack)
    cyc_i=1;stb_i=1;we_i=1;adr_i=1;dat_i=16'hABCD; @(posedge clk);#1; // E
    stb_i=0; we_i=0;
    @(posedge clk);#1; $display("E+1 stall=%b",stall_o);
    @(posedge clk);#1; $display("E+2 stall=%b",stall_o);
    @(posedge clk);#1; $display("E+3 ack=%b dat=%h (expect ack=1 dat=ABCD)",ack_o,dat_o);
    @(posedge clk);#1; $display("E+4 ack=%b dat=%h (expect 0)",ack_o,dat_o);
    // dropped write: cyc low at response
    cyc_i=0;@(posedge clk);#1;@(posedge clk);#1;
    cyc_i=1;stb_i=1;we_i=1;adr_i=2;dat_i=16'h00FF;@(posedge clk);#1; //accept write
    stb_i=0;cyc_i=0; // cyc low through response
    @(posedge clk);#1;@(posedge clk);#1;@(posedge clk);#1;
    $display("dropped-write resp edge: ack=%b dat=%h (expect 0/0)",ack_o,dat_o);
    // read slot2 to prove it committed despite dropped response
    cyc_i=1;stb_i=1;we_i=0;adr_i=2;@(posedge clk);#1;stb_i=0;
    @(posedge clk);#1;@(posedge clk);#1;
    $display("read slot2 dat=%h (expect nonzero=mix(2,00FF))",dat_o);
    $finish;
  end
endmodule
EOF
iverilog -g2012 -o /tmp/t2.out /app/dut.sv /tmp/tb2.sv && vvp /tmp/t2.out

output

E+1 stall=1
E+2 stall=1
E+3 ack=1 dat=abcd (expect ack=1 dat=ABCD)
E+4 ack=0 dat=0000 (expect 0)
dropped-write resp edge: ack=0 dat=0000 (expect 0/0)
read slot2 dat=ff00 (expect nonzero=mix(2,00FF))
/tmp/tb2.sv:27: $finish called at 166 (1s)

[stdout]
E+1 stall=1
E+2 stall=1
E+3 ack=1 dat=abcd (expect ack=1 dat=ABCD)
E+4 ack=0 dat=0000 (expect 0)
dropped-write resp edge: ack=0 dat=0000 (expect 0/0)
read slot2 dat=ff00 (expect nonzero=mix(2,00FF))
/tmp/tb2.sv:27: $finish called at 166 (1s)

All behaviors verified correctly: - **Clean write**: response at E+3 returns committed slot `ABCD`, `ack=1`; outputs are 0 outside the response edge. - **Stall**: high only after E+1 and E+2 of an accepted write. - **Dropped write** (cyc low at response edge): `ack/dat = 0`, but the write **still commits** , the follow-up read of slot 2 returns `mix(2,0x00FF) = ff00`. - **Read/write collision** (from the first test): read wins `dat_o`, write still commits. - **mix / lane** semantics match the reference model. The module is written to `/app/dut.sv`. Design summary: - **Storage**: four 16-bit `slot`s with per-slot `primed` bits. - **Read pipe** (2-deep): captures `mix(adr, slot)` (or 0 if unprimed) at accept, responds at E+2. - **Write pipe** (3-deep): commits at E+3 using the *pre-edge* slot value , `slot[adr] = mix(adr, old) ^ dat_i`, sets primed, and returns the committed value. - **Accept** = `cyc_i & stb_i & ~stall_o` (pre-edge stall), split into read/write by `we_i`. - **stall_o** `= wA_v | wB_v` (pre-edge), i.e. high while a write occupies the second/third pipeline stage → exactly after E+1 and E+2. - **Outputs** are registered, read-priority on shared edges, cyc-gated (writes commit regardless), and 0 elsewhere. All Verilog is synthesizable ASCII with no system tasks/functions, directives, or banned constructs, and no `_ref`/`_dut` identifiers.

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 5367 samples)
TEST reference_equivalence: PASS (all 5367 samples matched reference)
{"score": 1.000000, "results_file": "/tmp/h2t-grader-home.GFoBaI/runtime/cb_verifier_324-14379-21736-26899_324/results.jsonl"}

Reproduce this trial: git checkout 2f94510 && PYTHONPATH=src python3 scripts/build_site.py , then open trial/trial_c096bd8ef4794e8b. Re-running the agent live requires EVAL_PLATFORM_ENABLE_OAUTH_SMOKE=1 and is non-deterministic.

Trial trial_c096bd8ef4794e8b · verifier authoritative; classifier explanatory.