SyncValsverifier → artifact → classifier → verdict
SyncVals · Trajectory

round-robin-arbiter-grant

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 4583 samples matched reference)` and `TEST simulation_completed: PASS (Mismatches: 0 in 4583 samples)`. Agent wrote `/app/dut.sv` implementing `TopModule` with round-robin state (`ptr`) plus lock hold state (`hold`/`hidx`) and explicitly tested start order, lock drop, and dead-air behavior before finishing.
Root causeThe agent correctly derived the specified round-robin arbiter and lock semantics from the instruction and implemented a synthesizable SystemVerilog module. The tests compare the DUT against a behavioral reference across directed and randomized cycles, and the implementation matched completely.
RecommendationN/A - task is fine
Trajectory
Tool-by-tool agent trajectory
7 tool calls · 3 tool types · 15 steps
write a verilog module TopModule sharing one resource among four requesters. ports: clk, rst, req[3:0], lock, outputs grant[3:0], grant_valid. grant is one-hot; grant_valid marks cycles it names someone. the very first time all four ask at once, requester 0 wins. fairness is a circular queue: the one just served goes to the back. walk up from just past the last winner, wrapping 3 to 0; grant the first asker. all four asking forever gives 0,1,2,3,0,1,... a lone requester keeps winning; idle keeps your place. lock high on a granted cycle latches that winner: grant stays nailed to it, grant_valid high, while lock stays high; everyone else waits. lock with no grant does nothing. when lock drops the held winner still owns that cycle; sharing resumes next cycle just past it. a hold lives only while the held requester keeps asking. a held cycle with its req low, even the cycle lock drops, is dead air: grant 0, grant_valid 0, whoever else asks; the hold is over. sharing resumes next cycle just past the dead winner, it counts as served; a lock still high needs no re-arm, latching the next real winner by the start rule. rst is synchronous active-high: clears any hold, restarts the order. write plain synthesizable systemverilog to /app/dut.sv; no preprocessor directives, system tasks, or force/release; ascii only. graded by iverilog -g2012 against a hidden reference every cycle.
Looking at this spec, I'll design a round-robin arbiter with a lock/hold mechanism. Let me reason through the state machine, then write it. Key state: a scan pointer (`ptr` = where the next round-robin scan starts) plus a hold flag/index. Let me write it.
write · /app/dut.sv
module TopModule (
    input  logic       clk,
    input  logic       rst,
    input  logic [3:0] req,
    input  logic       lock,
    output logic [3:0] grant,
    output logic       grant_valid
);
    // ptr  : next round-robin scan start position
    // hold : currently latched onto a winner
    // hidx : the held winner's index
    logic [1:0] ptr;
    logic       hold;
    logic [1:0] hidx;

    logic [1:0] next_ptr;
    logic       next_hold;
    logic [1:0] next_hidx;

    // round-robin scan result
    logic       found;
    logic [1:0] win;
    integer     i;
    logic [1:0] idx;

    always_comb begin
        // scan up from ptr, wrapping, first asker wins
        found = 1'b0;
        win   = 2'b00;
        for (i = 0; i < 4; i = i + 1) begin
            idx = ptr + i[1:0];
            if (!found && req[idx]) begin
                found = 1'b1;
                win   = idx;
            end
        end

        // defaults
        grant       = 4'b0000;
        grant_valid = 1'b0;
        next_ptr    = ptr;
        next_hold   = hold;
        next_hidx   = hidx;

        if (hold) begin
            // A hold lives only while the held requester keeps asking.
            if (req[hidx]) begin
                grant       = (4'b0001 << hidx);
                grant_valid = 1'b1;
                if (lock) begin
                    // keep holding
                    next_hold = 1'b1;
                    next_hidx = hidx;
                    next_ptr  = hidx + 2'd1;
                end else begin
                    // lock dropped: held winner still owns this cycle,
                    // sharing resumes next cycle just past it
                    next_hold = 1'b0;
                    next_ptr  = hidx + 2'd1;
                end
            end else begin
                // held req low -> dead air regardless of lock;
                // counts as served, sharing resumes just past it
                grant       = 4'b0000;
                grant_valid = 1'b0;
                next_hold   = 1'b0;
                next_ptr    = hidx + 2'd1;
            end
        end else begin
            if (found) begin
                grant       = (4'b0001 << win);
                grant_valid = 1'b1;
                next_ptr    = win + 2'd1;
                if (lock) begin
                    // latch this winner
                    next_hold = 1'b1;
                    next_hidx = win;
                end else begin
                    next_hold = 1'b0;
                end
            end else begin
                // no asker: idle keeps your place; lock with no grant does nothing
                grant       = 4'b0000;
                grant_valid = 1'b0;
            end
        end
    end

    always_ff @(posedge clk) begin
        if (rst) begin
            // synchronous clear: restart order (scan starts at 0), drop hold
            ptr  <= 2'd0;
            hold <= 1'b0;
            hidx <= 2'd0;
        end else begin
            ptr  <= next_ptr;
            hold <= next_hold;
            hidx <= next_hidx;
        end
    end
endmodule
Let me verify it compiles with iverilog and sanity-test the key behaviors.
shell
cat > tb.sv <<'EOF'
module tb;
  logic clk, rst, lock;
  logic [3:0] req, grant;
  logic grant_valid;
  TopModule dut(.*);
  initial begin clk=0; forever #5 clk=~clk; end
  task step; @(posedge clk); #1; $display("t=%0t req=%b lock=%b grant=%b gv=%b",$time,req,lock,grant,grant_valid); endtask
  initial begin
    rst=1; req=0; lock=0; @(posedge clk); #1; rst=0;
    $display("-- all four, no lock: expect 0,1,2,3,0");
    req=4'b1111; lock=0;
    step;step;step;step;step;
    $display("-- lock winner 0 (all ask, lock high): expect grant stays 0");
    req=4'b1111; lock=1; step; step; step;
    $display("-- lock drops, req0 still high: owns this cycle then resume at 1");
    lock=0; step; step;
    $display("-- dead air test: lock winner then held req low");
    rst=1; step; rst=0; req=4'b1111; lock=1; step; step;
    $display("now drop req of held winner (whichever). set req to exclude idx served");
    req=4'b1110; step; // if held 0, dead air; grant0 gv0
    lock=0; req=4'b1111; step; step;
    $finish;
  end
endmodule
EOF
iverilog -g2012 -o sim dut.sv tb.sv && vvp sim
output
dut.sv:26: sorry: constant selects in always_* processes are not currently supported (all bits will be included).
-- all four, no lock: expect 0,1,2,3,0
t=16 req=1111 lock=0 grant=0010 gv=1
t=26 req=1111 lock=0 grant=0100 gv=1
t=36 req=1111 lock=0 grant=1000 gv=1
t=46 req=1111 lock=0 grant=0001 gv=1
t=56 req=1111 lock=0 grant=0010 gv=1
-- lock winner 0 (all ask, lock high): expect grant stays 0
t=66 req=1111 lock=1 grant=0010 gv=1
t=76 req=1111 lock=1 grant=0010 gv=1
t=86 req=1111 lock=1 grant=0010 gv=1
-- lock drops, req0 still high: owns this cycle then resume at 1
t=96 req=1111 lock=0 grant=0100 gv=1
t=106 req=1111 lock=0 grant=1000 gv=1
-- dead air test: lock winner then held req low
t=116 req=1111 lock=0 grant=0001 gv=1
t=126 req=1111 lock=1 grant=0001 gv=1
t=136 req=1111 lock=1 grant=0001 gv=1
now drop req of held winner (whichever). set req to exclude idx served
t=146 req=1110 lock=1 grant=0010 gv=1
t=156 req=1111 lock=0 grant=0100 gv=1
t=166 req=1111 lock=0 grant=1000 gv=1
tb.sv:22: $finish called at 166 (1s)

[stdout]
dut.sv:26: sorry: constant selects in always_* processes are not currently supported (all bits will be included).
-- all four, no lock: expect 0,1,2,3,0
t=16 req=1111 lock=0 grant=0010 gv=1
t=26 req=1111 lock=0 grant=0100 gv=1
t=36 req=1111 lock=0 grant=1000 gv=1
t=46 req=1111 lock=0 grant=0001 gv=1
t=56 req=1111 lock=0 grant=0010 gv=1
-- lock winner 0 (all ask, lock high): expect grant stays 0
t=66 req=1111 lock=1 grant=0010 gv=1
t=76 req=1111 lock=1 grant=0010 gv=1
t=86 req=1111 lock=1 grant=0010 gv=1
-- lock drops, req0 still high: owns this cycle then resume at 1
t=96 req=1111 lock=0 grant=0100 gv=1
t=106 req=1111 lock=0 grant=1000 gv=1
-- dead air test: lock winner then held req low
t=116 req=1111 lock=0 grant=0001 gv=1
t=126 req=1111 lock=1 grant=0001 gv=1
t=136 req=1111 lock=1 grant=0001 gv=1
now drop req of held winner (whichever). set req to exclude idx served
t=146 req=1110 lock=1 grant=0010 gv=1
t=156 req=1111 lock=0 grant=0100 gv=1
t=166 req=1111 lock=0 grant=1000 gv=1
tb.sv:22: $finish called at 166 (1s)
Two problems: iverilog flags `i[1:0]` (integer part-select in `always_*`) as unsupported, and the results are off by one because of it (first grant is index 1, should be 0). Let me rewrite the scan with explicit candidates , no integer bit-select.

/app/dut.sv

− removed
    // round-robin scan result
    logic       found;
    logic [1:0] win;
    integer     i;
    logic [1:0] idx;

    always_comb begin
        // scan up from ptr, wrapping, first asker wins
        found = 1'b0;
        win   = 2'b00;
        for (i = 0; i < 4; i = i + 1) begin
            idx = ptr + i[1:0];
            if (!found && req[idx]) begin
                found = 1'b1;
                win   = idx;
            end
        end
+ added
    // round-robin scan result
    logic       found;
    logic [1:0] win;
    logic [1:0] c0, c1, c2, c3;

    always_comb begin
        // scan up from ptr, wrapping, first asker wins
        c0 = ptr;
        c1 = ptr + 2'd1;
        c2 = ptr + 2'd2;
        c3 = ptr + 2'd3;
        found = 1'b0;
        win   = 2'b00;
        if (req[c0]) begin
            found = 1'b1; win = c0;
        end else if (req[c1]) begin
            found = 1'b1; win = c1;
        end else if (req[c2]) begin
            found = 1'b1; win = c2;
        end else if (req[c3]) begin
            found = 1'b1; win = c3;
        end
shell
iverilog -g2012 -o sim dut.sv tb.sv && vvp sim
output
-- all four, no lock: expect 0,1,2,3,0
t=16 req=1111 lock=0 grant=0010 gv=1
t=26 req=1111 lock=0 grant=0100 gv=1
t=36 req=1111 lock=0 grant=1000 gv=1
t=46 req=1111 lock=0 grant=0001 gv=1
t=56 req=1111 lock=0 grant=0010 gv=1
-- lock winner 0 (all ask, lock high): expect grant stays 0
t=66 req=1111 lock=1 grant=0010 gv=1
t=76 req=1111 lock=1 grant=0010 gv=1
t=86 req=1111 lock=1 grant=0010 gv=1
-- lock drops, req0 still high: owns this cycle then resume at 1
t=96 req=1111 lock=0 grant=0100 gv=1
t=106 req=1111 lock=0 grant=1000 gv=1
-- dead air test: lock winner then held req low
t=116 req=1111 lock=0 grant=0001 gv=1
t=126 req=1111 lock=1 grant=0001 gv=1
t=136 req=1111 lock=1 grant=0001 gv=1
now drop req of held winner (whichever). set req to exclude idx served
t=146 req=1110 lock=1 grant=0010 gv=1
t=156 req=1111 lock=0 grant=0100 gv=1
t=166 req=1111 lock=0 grant=1000 gv=1
tb.sv:22: $finish called at 166 (1s)

[stdout]
-- all four, no lock: expect 0,1,2,3,0
t=16 req=1111 lock=0 grant=0010 gv=1
t=26 req=1111 lock=0 grant=0100 gv=1
t=36 req=1111 lock=0 grant=1000 gv=1
t=46 req=1111 lock=0 grant=0001 gv=1
t=56 req=1111 lock=0 grant=0010 gv=1
-- lock winner 0 (all ask, lock high): expect grant stays 0
t=66 req=1111 lock=1 grant=0010 gv=1
t=76 req=1111 lock=1 grant=0010 gv=1
t=86 req=1111 lock=1 grant=0010 gv=1
-- lock drops, req0 still high: owns this cycle then resume at 1
t=96 req=1111 lock=0 grant=0100 gv=1
t=106 req=1111 lock=0 grant=1000 gv=1
-- dead air test: lock winner then held req low
t=116 req=1111 lock=0 grant=0001 gv=1
t=126 req=1111 lock=1 grant=0001 gv=1
t=136 req=1111 lock=1 grant=0001 gv=1
now drop req of held winner (whichever). set req to exclude idx served
t=146 req=1110 lock=1 grant=0010 gv=1
t=156 req=1111 lock=0 grant=0100 gv=1
t=166 req=1111 lock=0 grant=1000 gv=1
tb.sv:22: $finish called at 166 (1s)
Compiles clean now. The "off by one" is a testbench sampling artifact , I'm displaying *after* the edge, so I miss the first cycle. Let me sample mid-cycle (negedge) instead to see the true per-cycle grants.
shell
cat > tb.sv <<'EOF'
module tb;
  logic clk, rst, lock;
  logic [3:0] req, grant;
  logic grant_valid;
  TopModule dut(.*);
  initial begin clk=0; forever #5 clk=~clk; end
  // drive on posedge region, sample on negedge (stable, current cycle)
  task cyc(input [3:0] r, input l, input string note);
    req=r; lock=l; @(negedge clk);
    $display("req=%b lock=%b -> grant=%b gv=%b   %s",req,lock,grant,grant_valid,note);
    @(posedge clk);
  endtask
  initial begin
    rst=1; req=0; lock=0; @(negedge clk); @(posedge clk); rst=0;
    $display("-- all four, no lock: expect 0,1,2,3,0,1");
    cyc(4'b1111,0,"exp 0001");
    cyc(4'b1111,0,"exp 0010");
    cyc(4'b1111,0,"exp 0100");
    cyc(4'b1111,0,"exp 1000");
    cyc(4'b1111,0,"exp 0001");
    cyc(4'b1111,0,"exp 0010");
    $display("-- lone requester (only 2): keeps winning");
    cyc(4'b0100,0,"exp 0100");
    cyc(4'b0100,0,"exp 0100");
    $display("-- idle keeps place, then req all: resume just past 2 -> 3");
    cyc(4'b0000,0,"exp 0000 gv0");
    cyc(4'b1111,0,"exp 1000 (idx3)");
    $display("-- reset, lock winner0");
    rst=1; @(negedge clk); @(posedge clk); rst=0;
    cyc(4'b1111,1,"exp 0001 latch");
    cyc(4'b1111,1,"exp 0001 held");
    cyc(4'b1111,1,"exp 0001 held");
    $display("-- lock drops, held req high: owns cycle, then resume at 1");
    cyc(4'b1111,0,"exp 0001 (last owned)");
    cyc(4'b1111,0,"exp 0010 (idx1)");
    $display("-- reset, lock winner0 then dead air (req0 low)");
    rst=1; @(negedge clk); @(posedge clk); rst=0;
    cyc(4'b1111,1,"exp 0001 latch");
    cyc(4'b1110,1,"exp 0000 gv0 dead air (lock still high)");
    cyc(4'b1111,1,"exp 0010 relatch idx1 (resume past dead 0)");
    cyc(4'b1111,1,"exp 0010 held");
    $display("-- lock high but no grant: does nothing");
    rst=1; @(negedge clk); @(posedge clk); rst=0;
    cyc(4'b0000,1,"exp 0000 gv0");
    cyc(4'b1111,0,"exp 0001 (place kept at 0)");
    $finish;
  end
endmodule
EOF
iverilog -g2012 -o sim dut.sv tb.sv && vvp sim
output
-- all four, no lock: expect 0,1,2,3,0,1
req=1111 lock=0 -> grant=0001 gv=1   exp 0001
req=1111 lock=0 -> grant=0010 gv=1   exp 0010
req=1111 lock=0 -> grant=0100 gv=1   exp 0100
req=1111 lock=0 -> grant=1000 gv=1   exp 1000
req=1111 lock=0 -> grant=0001 gv=1   exp 0001
req=1111 lock=0 -> grant=0010 gv=1   exp 0010
-- lone requester (only 2): keeps winning
req=0100 lock=0 -> grant=0100 gv=1   exp 0100
req=0100 lock=0 -> grant=0100 gv=1   exp 0100
-- idle keeps place, then req all: resume just past 2 -> 3
req=0000 lock=0 -> grant=0000 gv=0   exp 0000 gv0
req=1111 lock=0 -> grant=1000 gv=1   exp 1000 (idx3)
-- reset, lock winner0
req=1111 lock=1 -> grant=0010 gv=1   exp 0001 latch
req=1111 lock=1 -> grant=0010 gv=1   exp 0001 held
req=1111 lock=1 -> grant=0010 gv=1   exp 0001 held
-- lock drops, held req high: owns cycle, then resume at 1
req=1111 lock=0 -> grant=0010 gv=1   exp 0001 (last owned)
req=1111 lock=0 -> grant=0100 gv=1   exp 0010 (idx1)
-- reset, lock winner0 then dead air (req0 low)
req=1111 lock=1 -> grant=0001 gv=1   exp 0001 latch
req=1110 lock=1 -> grant=0000 gv=0   exp 0000 gv0 dead air (lock still high)
req=1111 lock=1 -> grant=0010 gv=1   exp 0010 relatch idx1 (resume past dead 0)
req=1111 lock=1 -> grant=0010 gv=1   exp 0010 held
-- lock high but no grant: does nothing
req=0000 lock=1 -> grant=0000 gv=0   exp 0000 gv0
req=1111 lock=0 -> grant=0100 gv=1   exp 0001 (place kept at 0)
tb.sv:46: $finish called at 255 (1s)

[stdout]
-- all four, no lock: expect 0,1,2,3,0,1
req=1111 lock=0 -> grant=0001 gv=1   exp 0001
req=1111 lock=0 -> grant=0010 gv=1   exp 0010
req=1111 lock=0 -> grant=0100 gv=1   exp 0100
req=1111 lock=0 -> grant=1000 gv=1   exp 1000
req=1111 lock=0 -> grant=0001 gv=1   exp 0001
req=1111 lock=0 -> grant=0010 gv=1   exp 0010
-- lone requester (only 2): keeps winning
req=0100 lock=0 -> grant=0100 gv=1   exp 0100
req=0100 lock=0 -> grant=0100 gv=1   exp 0100
-- idle keeps place, then req all: resume just past 2 -> 3
req=0000 lock=0 -> grant=0000 gv=0   exp 0000 gv0
req=1111 lock=0 -> grant=1000 gv=1   exp 1000 (idx3)
-- reset, lock winner0
req=1111 lock=1 -> grant=0010 gv=1   exp 0001 latch
req=1111 lock=1 -> grant=0010 gv=1   exp 0001 held
req=1111 lock=1 -> grant=0010 gv=1   exp 0001 held
-- lock drops, held req high: owns cycle, then resume at 1
req=1111 lock=0 -> grant=0010 gv=1   exp 0001 (last owned)
req=1111 lock=0 -> grant=0100 gv=1   exp 0010 (idx1)
-- reset, lock winner0 then dead air (req0 low)
req=1111 lock=1 -> grant=0001 gv=1   exp 0001 latch
req=1110 lock=1 -> grant=0000 gv=0   exp 0000 gv0 dead air (lock still high)
req=1111 lock=1 -> grant=0010 gv=1   exp 0010 relatch idx1 (resume past dead 0)
req=1111 lock=1 -> grant=0010 gv=1   exp 0010 held
-- lock high but no grant: does nothing
req=0000 lock=1 -> grant=0000 gv=0   exp 0000 gv0
req=1111 lock=0 -> grant=0100 gv=1   exp 0001 (place kept at 0)
tb.sv:46: $finish called at 255 (1s)
Most cases pass, but two reset blocks show an off-by-one (`0010` where I expected `0001`). Let me probe internal state to see whether it's the DUT or my testbench's reset timing.
shell
cat > tb2.sv <<'EOF'
module tb2;
  logic clk, rst, lock;
  logic [3:0] req, grant;
  logic grant_valid;
  TopModule dut(.*);
  initial begin clk=0; forever #5 clk=~clk; end
  task cyc(input [3:0] r, input l, input string note);
    req=r; lock=l; @(negedge clk);
    $display("ptr=%0d hold=%b hidx=%0d | req=%b lock=%b -> grant=%b gv=%b  %s",
             dut.ptr,dut.hold,dut.hidx,req,lock,grant,grant_valid,note);
    @(posedge clk);
  endtask
  task doreset;
    req=0; lock=0; rst=1; @(posedge clk); #1; rst=0;
  endtask
  initial begin
    doreset;
    $display("-- reset then lock winner0 + dead air");
    cyc(4'b1111,1,"exp 0001 latch");
    cyc(4'b1110,1,"exp 0000 gv0 dead air");
    cyc(4'b1111,1,"exp 0010 relatch idx1");
    cyc(4'b1111,1,"exp 0010 held");
    doreset;
    $display("-- reset then lock hold, drop lock");
    cyc(4'b1111,1,"exp 0001 latch");
    cyc(4'b1111,1,"exp 0001 held");
    cyc(4'b1111,0,"exp 0001 last owned");
    cyc(4'b1111,0,"exp 0010 resume idx1");
    $finish;
  end
endmodule
EOF
iverilog -g2012 -o sim2 dut.sv tb2.sv && vvp sim2
output
-- reset then lock winner0 + dead air
ptr=0 hold=0 hidx=0 | req=1111 lock=1 -> grant=0001 gv=1  exp 0001 latch
ptr=1 hold=1 hidx=0 | req=1110 lock=1 -> grant=0000 gv=0  exp 0000 gv0 dead air
ptr=1 hold=0 hidx=0 | req=1111 lock=1 -> grant=0010 gv=1  exp 0010 relatch idx1
ptr=2 hold=1 hidx=1 | req=1111 lock=1 -> grant=0010 gv=1  exp 0010 held
-- reset then lock hold, drop lock
ptr=0 hold=0 hidx=0 | req=1111 lock=1 -> grant=0001 gv=1  exp 0001 latch
ptr=1 hold=1 hidx=0 | req=1111 lock=1 -> grant=0001 gv=1  exp 0001 held
ptr=1 hold=1 hidx=0 | req=1111 lock=0 -> grant=0001 gv=1  exp 0001 last owned
ptr=1 hold=0 hidx=0 | req=1111 lock=0 -> grant=0010 gv=1  exp 0010 resume idx1
tb2.sv:29: $finish called at 95 (1s)

[stdout]
-- reset then lock winner0 + dead air
ptr=0 hold=0 hidx=0 | req=1111 lock=1 -> grant=0001 gv=1  exp 0001 latch
ptr=1 hold=1 hidx=0 | req=1110 lock=1 -> grant=0000 gv=0  exp 0000 gv0 dead air
ptr=1 hold=0 hidx=0 | req=1111 lock=1 -> grant=0010 gv=1  exp 0010 relatch idx1
ptr=2 hold=1 hidx=1 | req=1111 lock=1 -> grant=0010 gv=1  exp 0010 held
-- reset then lock hold, drop lock
ptr=0 hold=0 hidx=0 | req=1111 lock=1 -> grant=0001 gv=1  exp 0001 latch
ptr=1 hold=1 hidx=0 | req=1111 lock=1 -> grant=0001 gv=1  exp 0001 held
ptr=1 hold=1 hidx=0 | req=1111 lock=0 -> grant=0001 gv=1  exp 0001 last owned
ptr=1 hold=0 hidx=0 | req=1111 lock=0 -> grant=0010 gv=1  exp 0010 resume idx1
tb2.sv:29: $finish called at 95 (1s)
With a proper reset, every spec behavior checks out. The earlier "off-by-one" was purely my first testbench's sloppy reset sequence (it never reliably clocked a posedge with `rst=1`); the DUT itself is correct. Confirmed behaviors: - **Start rule / round-robin:** all four asking → `0,1,2,3,0,1,…` - **Lone requester** keeps winning; **idle keeps its place** (pointer unchanged, `grant_valid=0`) - **Lock latch:** lock high on a granted cycle nails grant to that winner while lock stays high - **Lock drop:** held winner still owns that cycle, sharing resumes next cycle just past it - **Dead air:** held requester drops its req → `grant=0, grant_valid=0` regardless of lock/others; counts as served, resumes just past it; a still-high lock re-latches the next real winner with no re-arm Let me clean up the scratch test files.
shell
rm -f tb.sv tb2.sv sim sim2; ls /app
output
dut.sv

[stdout]
dut.sv
Done. `/app/dut.sv` contains the complete `TopModule`. **Design summary** , three registers of state: - `ptr` , where the next round-robin scan starts (init `0`, so the first all-ask cycle grants requester 0) - `hold` / `hidx` , whether a winner is latched and which one **Combinational logic:** - **Not holding:** scan `ptr, ptr+1, ptr+2, ptr+3` (wrapping) for the first asker → one-hot `grant`, `grant_valid=1`, `next_ptr = win+1`. If `lock` is high on that granted cycle, latch it (`hold=1, hidx=win`). No asker → dead cycle, pointer held (lock with no grant does nothing). - **Holding on `hidx`:** if `req[hidx]` still high → grant stays nailed to it, `grant_valid=1`; keep holding while `lock` high, else release (winner still owns this cycle, `ptr→hidx+1`). If `req[hidx]` is low → dead air (`grant=0, grant_valid=0`) regardless of lock or other requesters, hold ends, `ptr→hidx+1` (counts as served). A still-high lock naturally re-latches the next real winner via the normal scan. `rst` is synchronous active-high , clears `hold` and resets `ptr=0`. The file is plain synthesizable SystemVerilog: no preprocessor directives, system tasks, or force/release, ASCII only, and compiles cleanly 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_elaborates: PASS (DUT elaborates standalone)
TEST dut_compiles: PASS (compiled with held-back reference/testbench)
TEST simulation_completed: PASS (Mismatches: 0 in 4583 samples)
TEST reference_equivalence: PASS (all 4583 samples matched reference)
{"score": 1.000000, "results_file": "/tmp/h2t-grader-home.jD7pqG/runtime/cb_verifier_332-26336-4944-19833_332/results.jsonl"}

Reproduce this trial: git checkout 2f94510 && PYTHONPATH=src python3 scripts/build_site.py , then open trial/trial_b1912327343448f0. Re-running the agent live requires EVAL_PLATFORM_ENABLE_OAUTH_SMOKE=1 and is non-deterministic.

Trial trial_b1912327343448f0 · verifier authoritative; classifier explanatory.