SyncVals · Trajectory

apb-lite-slave-regfile

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 required an APB-like TopModule with mapped words 0-3, word-1 low-byte storage, word-2 constant 32'h0AB15001, off-map pslverr, and word-3 one-cycle wait behavior. Agent wrote /app/dut.sv implementing those behaviors, including `pready = word3_waited` for paddr 3 and writes to word3 only when `word3_waited`. Verifier output: `TEST reference_equivalence: PASS (all 2508 samples matched reference)` and result reward was 1.0.

Root causeThe agent implemented the specified register-file behavior directly from the instructions and validated it with its own sanity testbench. The hidden tests checked behavioral equivalence against a reference model rather than superficial implementation details, and the submitted design matched all sampled cases.

RecommendationN/A - task is fine

Trajectory

Tool-by-tool agent trajectory

4 tool calls · 2 tool types · 9 steps

Write /app/dut.sv defining TopModule with ports clk, rst, psel, penable, pwrite, paddr[3:0], pwdata[31:0], prdata[31:0], pready, and pslverr. rst is synchronous active high. The master uses APB setup then access: setup has psel=1, penable=0; access has psel=1, penable=1 with address, write bit, and data held stable. Only access cycles can complete transfers. While rst is high, clear writable registers and drive pready=0, pslverr=0, prdata=0. Addresses 0, 1, 2, and 3 are valid word indexes. Word 0 and word 3 are normal read/write registers reset to 0. Word 1 stores only pwdata[7:0]; reads return {24'd0, stored_low_byte}. Word 2 is read-only and always returns 32'h0AB15001; writes to it are accepted but ignored. Off-map accesses (paddr>=4) complete with pready=1, pslverr=1, prdata=0, and no register change. Mapped words 0, 1, and 2 complete on their first access cycle with pready=1. Each word-3 transaction inserts one wait access cycle: the first access cycle has pready=0; every later access cycle of that same held transaction has pready=1 until psel or penable falls. Writes update only on an access cycle where pready=1 and pslverr=0. For mapped reads, prdata is the current register value during access; outside mapped read access it is 0. The grader checks pready/pslverr only on access cycles and prdata only on read access cycles. Helper modules are allowed. 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  wire        clk,
    input  wire        rst,
    input  wire        psel,
    input  wire        penable,
    input  wire        pwrite,
    input  wire [3:0]  paddr,
    input  wire [31:0] pwdata,
    output reg  [31:0] prdata,
    output reg         pready,
    output reg         pslverr
);

    // Writable registers
    reg [31:0] word0;
    reg [7:0]  word1_low;
    reg [31:0] word3;

    // Wait-state tracking for word 3: 0 during the first access cycle of a
    // held word-3 transaction, 1 during every later access cycle.
    reg word3_waited;

    localparam [31:0] WORD2_VAL = 32'h0AB15001;

    wire access = psel & penable;

    // -----------------------------------------------------------------
    // Combinational outputs
    // -----------------------------------------------------------------
    always @(*) begin
        prdata  = 32'd0;
        pready  = 1'b0;
        pslverr = 1'b0;

        if (rst) begin
            // Held reset values while rst is high
            prdata  = 32'd0;
            pready  = 1'b0;
            pslverr = 1'b0;
        end else if (access) begin
            if (paddr >= 4'd4) begin
                // Off-map: complete with error, no data
                pready  = 1'b1;
                pslverr = 1'b1;
                prdata  = 32'd0;
            end else if (paddr == 4'd3) begin
                // Word 3: one wait access cycle
                pready  = word3_waited;
                pslverr = 1'b0;
                if (!pwrite)
                    prdata = word3;
            end else begin
                // Words 0,1,2 complete on first access cycle
                pready  = 1'b1;
                pslverr = 1'b0;
                if (!pwrite) begin
                    case (paddr)
                        4'd0: prdata = word0;
                        4'd1: prdata = {24'd0, word1_low};
                        4'd2: prdata = WORD2_VAL;
                        default: prdata = 32'd0;
                    endcase
                end
            end
        end
    end

    // -----------------------------------------------------------------
    // Sequential state
    // -----------------------------------------------------------------
    always @(posedge clk) begin
        if (rst) begin
            word0        <= 32'd0;
            word1_low    <= 8'd0;
            word3        <= 32'd0;
            word3_waited <= 1'b0;
        end else begin
            // Track word-3 wait state
            if (access && (paddr == 4'd3))
                word3_waited <= 1'b1;
            else
                word3_waited <= 1'b0;

            // Writes commit only on an access cycle where pready=1 && pslverr=0
            if (access && pwrite) begin
                case (paddr)
                    4'd0: word0     <= pwdata;
                    4'd1: word1_low <= pwdata[7:0];
                    // word 2 accepted but ignored
                    4'd3: if (word3_waited) word3 <= pwdata;
                    default: ; // off-map: no register change
                endcase
            end
        end
    end

endmodule

I've written `/app/dut.sv`. Let me verify it compiles.

Compile the SystemVerilog module

shell

(iverilog -g2012 -o /tmp/dut.out 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 self-check testbench to validate the key behaviors.

Run sanity testbench

shell

cat > /tmp/tb.sv <<'EOF'
module tb;
  reg clk=0, rst, psel, penable, pwrite;
  reg [3:0] paddr; reg [31:0] pwdata;
  wire [31:0] prdata; wire pready, pslverr;
  TopModule d(.clk(clk),.rst(rst),.psel(psel),.penable(penable),.pwrite(pwrite),
    .paddr(paddr),.pwdata(pwdata),.prdata(prdata),.pready(pready),.pslverr(pslverr));
  always #5 clk=~clk;
  task setup(input [3:0] a, input wr, input [31:0] d);
    begin psel=1;penable=0;pwrite=wr;paddr=a;pwdata=d; @(posedge clk); end
  endtask
  task acc; begin penable=1; @(posedge clk); end endtask
  task idle; begin psel=0;penable=0; @(posedge clk); end endtask
  initial begin
    rst=1;psel=0;penable=0;pwrite=0;paddr=0;pwdata=0;
    @(posedge clk); rst=0; @(posedge clk);
    // write word0=0xDEAD
    setup(0,1,32'hDEAD); #1; acc; #1; $display("w0 acc pready=%b slverr=%b",pready,pslverr); idle;
    // read word0
    setup(0,0,0); acc; #1; $display("r0 prdata=%h pready=%b (exp DEAD,1)",prdata,pready); idle;
    // write word1=0x1234ABCD -> low CD
    setup(1,1,32'h1234ABCD); acc; idle;
    setup(1,0,0); acc; #1; $display("r1 prdata=%h (exp 000000CD)",prdata); idle;
    // read word2
    setup(2,0,0); acc; #1; $display("r2 prdata=%h slverr=%b (exp 0AB15001,0)",prdata,pslverr); idle;
    // word2 write ignored, still returns const
    setup(2,1,32'hFFFF); acc; idle;
    setup(2,0,0); acc; #1; $display("r2b prdata=%h (exp 0AB15001)",prdata); idle;
    // off map
    setup(5,0,0); acc; #1; $display("off pready=%b slverr=%b prdata=%h (exp 1,1,0)",pready,pslverr,prdata); idle;
    // word3 write with wait state: first acc pready=0, second pready=1
    setup(3,1,32'hCAFEF00D); #1;
    acc; #1; $display("w3 acc1 pready=%b (exp 0)",pready);
    acc; #1; $display("w3 acc2 pready=%b (exp 1)",pready); idle;
    // read word3 back
    setup(3,0,0);
    acc; #1; $display("r3 acc1 pready=%b prdata=%h (exp 0,CAFEF00D)",pready,prdata);
    acc; #1; $display("r3 acc2 pready=%b prdata=%h (exp 1,CAFEF00D)",pready,prdata); idle;
    $finish;
  end
endmodule
EOF
iverilog -g2012 -o /tmp/t.out /tmp/tb.sv /app/dut.sv && vvp /tmp/t.out

output

w0 acc pready=1 slverr=0
r0 prdata=0000dead pready=1 (exp DEAD,1)
r1 prdata=000000cd (exp 000000CD)
r2 prdata=0ab15001 slverr=0 (exp 0AB15001,0)
r2b prdata=0ab15001 (exp 0AB15001)
off pready=1 slverr=1 prdata=00000000 (exp 1,1,0)
w3 acc1 pready=1 (exp 0)
w3 acc2 pready=1 (exp 1)
r3 acc1 pready=1 prdata=cafef00d (exp 0,CAFEF00D)
r3 acc2 pready=1 prdata=cafef00d (exp 1,CAFEF00D)
/tmp/tb.sv:38: $finish called at 335 (1s)

[stdout]
w0 acc pready=1 slverr=0
r0 prdata=0000dead pready=1 (exp DEAD,1)
r1 prdata=000000cd (exp 000000CD)
r2 prdata=0ab15001 slverr=0 (exp 0AB15001,0)
r2b prdata=0ab15001 (exp 0AB15001)
off pready=1 slverr=1 prdata=00000000 (exp 1,1,0)
w3 acc1 pready=1 (exp 0)
w3 acc2 pready=1 (exp 1)
r3 acc1 pready=1 prdata=cafef00d (exp 0,CAFEF00D)
r3 acc2 pready=1 prdata=cafef00d (exp 1,CAFEF00D)
/tmp/tb.sv:38: $finish called at 335 (1s)

The word3 test shows a sampling-timing artifact in my testbench , I displayed `pready` *after* the clock edge that ends the first access cycle, so I was reading the second access cycle. Let me fix the testbench sampling to check `pready` during the access cycle (before the edge).

Word3 wait-state timing check

shell

cat > /tmp/tb2.sv <<'EOF'
module tb;
  reg clk=0, rst, psel, penable, pwrite;
  reg [3:0] paddr; reg [31:0] pwdata;
  wire [31:0] prdata; wire pready, pslverr;
  TopModule d(.clk(clk),.rst(rst),.psel(psel),.penable(penable),.pwrite(pwrite),
    .paddr(paddr),.pwdata(pwdata),.prdata(prdata),.pready(pready),.pslverr(pslverr));
  always #5 clk=~clk;
  // drive signals just after posedge; sample combinationally before next posedge
  task setup(input [3:0] a, input wr, input [31:0] d);
    begin psel=1;penable=0;pwrite=wr;paddr=a;pwdata=d; @(posedge clk); end
  endtask
  // enter access, sample near end of this cycle (before next edge), then advance
  task acc(output rdy, output slv, output [31:0] rd);
    begin penable=1; #8; rdy=pready; slv=pslverr; rd=prdata; @(posedge clk); end
  endtask
  task idle; begin psel=0;penable=0; @(posedge clk); end endtask
  reg r; reg s; reg [31:0] pd;
  initial begin
    rst=1;psel=0;penable=0;pwrite=0;paddr=0;pwdata=0;
    @(posedge clk); rst=0; @(posedge clk);
    setup(3,1,32'hCAFEF00D);
    acc(r,s,pd); $display("w3 acc1 pready=%b (exp 0)",r);
    acc(r,s,pd); $display("w3 acc2 pready=%b (exp 1)",r); idle;
    setup(3,0,0);
    acc(r,s,pd); $display("r3 acc1 pready=%b prdata=%h (exp 0,CAFEF00D)",r,pd);
    acc(r,s,pd); $display("r3 acc2 pready=%b prdata=%h (exp 1,CAFEF00D)",r,pd); idle;
    // second independent word3 txn must wait again
    setup(3,0,0);
    acc(r,s,pd); $display("r3b acc1 pready=%b (exp 0)",r); idle;
    $finish;
  end
endmodule
EOF
iverilog -g2012 -o /tmp/t2.out /tmp/tb2.sv /app/dut.sv && vvp /tmp/t2.out

output

w3 acc1 pready=0 (exp 0)
w3 acc2 pready=1 (exp 1)
r3 acc1 pready=0 prdata=cafef00d (exp 0,CAFEF00D)
r3 acc2 pready=1 prdata=cafef00d (exp 1,CAFEF00D)
r3b acc1 pready=0 (exp 0)
/tmp/tb2.sv:30: $finish called at 125 (1s)

[stdout]
w3 acc1 pready=0 (exp 0)
w3 acc2 pready=1 (exp 1)
r3 acc1 pready=0 prdata=cafef00d (exp 0,CAFEF00D)
r3 acc2 pready=1 prdata=cafef00d (exp 1,CAFEF00D)
r3b acc1 pready=0 (exp 0)
/tmp/tb2.sv:30: $finish called at 125 (1s)

All behaviors verified correctly: - **Word 0/3**: normal read/write, reset to 0. - **Word 1**: stores only `pwdata[7:0]`, reads return `{24'd0, low_byte}` (`0x1234ABCD` → `0x000000CD`). - **Word 2**: read-only constant `0x0AB15001`; writes accepted but ignored. - **Off-map (≥4)**: `pready=1`, `pslverr=1`, `prdata=0`, no register change. - **Words 0/1/2**: complete on first access cycle (`pready=1`). - **Word 3 wait state**: first access cycle `pready=0`, subsequent access cycles of the same held transaction `pready=1`; the write commits only when `pready=1`. A fresh word-3 transaction inserts the wait again (`r3b acc1 pready=0`). - **Reset**: synchronous, clears writable registers and drives `pready=0`/`pslverr=0`/`prdata=0`. `/app/dut.sv` is complete and compiles cleanly under `iverilog -g2012`. The design is a single `TopModule`: - A combinational block drives `prdata`/`pready`/`pslverr` (only meaningful during access cycles, forced to 0 under `rst`), returning register values on mapped reads and 0 otherwise. - A synchronous block tracks the word-3 wait flag (`word3_waited`, set after the first access cycle of a held word-3 transaction, cleared whenever the cycle isn't a word-3 access) and commits writes only on access cycles where `pready=1 && pslverr=0`.

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 (DUT snapshotted before any observable path)
TEST dut_forbidden: PASS (no forbidden constructs)
TEST dut_elaborates: PASS (DUT elaborates standalone with TopModule as sole root)
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 2508 samples)
TEST reference_equivalence: PASS (all 2508 samples matched reference)

Reproduce this trial: git checkout 2f94510 && PYTHONPATH=src python3 scripts/build_site.py , then open trial/trial_c9eb8e7d011845c0. Re-running the agent live requires EVAL_PLATFORM_ENABLE_OAUTH_SMOKE=1 and is non-deterministic.

Trial trial_c9eb8e7d011845c0 · verifier authoritative; classifier explanatory.