SyncValsverifier → artifact → classifier → verdict
SyncVals · Trajectory

Multi-cycle signed divider with a start/valid handshake

codex gpt-5.5 ✗ 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.
SubtypeWrong Approach or Implementation Bug
EvidenceAgent implemented a complete signed divider with floored division, special case handling, and proper reset behavior. The implementation elaborated under iverilog -g2012 and passed the agent's own local directed test bench (7 sign quadrants, divide-by-zero, -32768/-1 overflow). However, it failed the verifier tests with reward=0.0. The core issue likely stems from counter timing: the agent's `cnt` field starts at 1 and counts to N_COUNT (16), but the specification's example shows the result should appear exactly N clocks after the accept edge. The latency calculation appears to be off by one cycle, which would fail cycle-by-cycle comparison against a reference model, particularly affecting back-to-back divides and the exact busy/valid handshake edges.
Root causeThe agent failed to achieve exact cycle-timing correspondence with the specification's latency diagram. While the implementation correctly captures operands, implements floored division, handles special cases, and manages the handshake structure, a subtle off-by-one error in counter initialization or comparison logic caused the result to appear at the wrong cycle relative to the accept edge, causing systematic failure across all verifier test cases.
RecommendationN/A - task is fine. The specification is clear and precise about cycle timing (diagram lines 62-68). The agent's approach was sound but the execution had a timing bug. A competent engineer would notice the failure immediately (score 0/100) and debug the counter logic by checking when cnt reaches N_COUNT relative to the specification's edge diagram, then fix the initialization or comparison to match the exact cycle count.
Trajectory
Tool-by-tool agent trajectory
20 tool calls · 2 tool types · 37 steps
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# Multi-cycle signed divider with a start/valid handshake ## Context We need the integer divide block `sdiv` for a small control core. Division is too slow to do in one clock at our target frequency, so it runs over several cycles behind a simple handshake: the core raises `start` for a cycle to hand us a signed dividend and divisor, the block goes busy while it grinds through the divide, and when the answer is ready it raises `valid` for one cycle with the signed quotient and remainder on the output ports. The thing that makes this block fiddly is that the operands captured at `start`, the busy/valid handshake, the fixed result latency and the exact sign rule for the quotient/remainder all have to line up: a result has to come from the numbers that were on the ports when the divide was accepted, not whatever is there N cycles later, and the handshake has to stay clean while that happens. The package and the wrapper are in place; only `rtl/sdiv.sv` is a stub. Implement it. ## Interface ``` input clk // single clock input rst_n // asynchronous, active low input start // request a divide (one-cycle pulse) input signed [15:0] dividend // two's-complement dividend input signed [15:0] divisor // two's-complement divisor output signed [15:0] quotient // two's-complement quotient output signed [15:0] remainder // two's-complement remainder output busy // a divide is in progress output valid // result-ready strobe (one cycle) ``` The word width is 16 and the result latency is `N = 16` clocks; both come from the package as `W` and `N`. ## Handshake and latency A divide is **accepted** on a rising edge of `clk` where `start` is high **and the block is not busy**. On that accepting edge the `dividend` and `divisor` then present on the ports are captured; the result is computed from those captured operands and from nothing else. Whatever appears on `dividend`/`divisor` after the accepting edge has no effect on the in-flight divide. - `valid` is high for **exactly one clock**, on the edge that is `N` clocks after the accepting edge, and `quotient`/`remainder` carry the result on that same clock. They are don't-care on every other clock. - `busy` is high from the clock **after** the accepting edge up to and including the clock **before** `valid`, and is low otherwise. `busy` and `valid` are **never high on the same clock**. - A `start` pulse that arrives while the block is **busy** is **ignored**: it does not restart, re-capture, or extend the divide in progress. For an accept on edge `A` (so `start` was high and the block was idle at `A`), the handshake runs like this (`N = 16`): ``` edge A A+1 A+2 ... A+15 A+16 start 1 x x ... x x busy 0 1 1 ... 1 0 valid 0 0 0 ... 0 1 quotient - - - ... - result remainder - - - ... - result ``` (The internal algorithm is yours; only this I/O behaviour is checked. The latency is `N` clocks regardless of the operands -- including divide-by-zero.) ## The division convention (read this carefully) The quotient and remainder use **floored** division, **not** the truncating convention that C and Verilog's own `/` and `%` use. Precisely, for a nonzero divisor: - `quotient = floor(dividend / divisor)` -- rounded toward **minus infinity**, not toward zero. So a negative result with a nonzero remainder rounds **down** (more negative): `-7 / 3` gives a quotient of `-3`, not `-2`. - `remainder = dividend - quotient * divisor`. With the floored quotient this makes the **remainder carry the sign of the divisor** (`0 <= remainder` when the divisor is positive, `remainder <= 0` when the divisor is negative). It does **not** take the sign of the dividend. - The identity `dividend == quotient * divisor + remainder` holds for every sign combination. Worked sign quadrants (all four use the rules above): ``` 7 / 3 -> quotient = 2, remainder = 1 -7 / 3 -> quotient = -3, remainder = 2 7 / -3 -> quotient = -3, remainder = -2 -7 / -3 -> quotient = 2, remainder = -1 ``` Note that Verilog's signed `/` truncates toward zero and signed `%` takes the sign of the dividend, so a direct `dividend / divisor` / `dividend % divisor` gives the **wrong** convention here on mixed signs; if you build the result that way you must correct it to the floored convention explicitly. ## Divide by zero and overflow These are defined results delivered on `valid` at the **same** `N`-clock latency as any other divide -- the block must not stall or hang: - **divisor == 0**: `quotient` saturates to `16'h7FFF` (+32767) if `dividend >= 0`, or `16'h8000` (-32768) if `dividend < 0`; `remainder` equals the `dividend`. - **dividend == -32768 and divisor == -1** (the one case whose true quotient, +32768, does not fit a signed 16-bit word): `quotient` saturates to `16'h7FFF` (+32767) and `remainder` is `0`. ## Conventions (pin these exactly) 1. **`quotient`, `remainder`, `busy`, `valid` are all registered.** Each takes its new value on a rising `clk` edge and holds it until the next edge that changes it; none is a combinational function of the current inputs. 2. **`valid` is a one-cycle pulse**, high only on the result edge. **`busy` is a level**, high for the whole in-flight window and never overlapping `valid`. 3. **Operands are captured on the accepting edge and held** for the entire divide; the result is a function of the captured operands only. The result bus (`quotient`/`remainder`) is meaningful only on the `valid` clock. 4. **State changes commit on the rising edge of `clk`** (accept, the latency count, and presenting the result). A `start` while busy commits nothing. 5. **`rst_n` is asynchronous and active low.** While it is low, `busy`, `valid`, `quotient` and `remainder` are all forced to `0` and the block returns to idle, immediately on the falling edge of `rst_n` rather than waiting for a clock. Reset takes priority over `start`. ## Submission Write your implementation into `rtl/sdiv.sv`, keeping the module name, ports and parameters exactly as given. It must elaborate under Icarus Verilog 11 (`iverilog -g2012`); note that on that tool a bit- or part-select of an *expression* (a sum, a shift, a function result) is a syntax error, so do any such bit work inside a `function automatic` on a named value, and write negative full-scale constants as bit patterns (`16'h8000` for -32768) rather than `-16'sd32768`. The grader compiles your block with a held-back checker and compares `busy` and `valid` every cycle, and `quotient`/`remainder` on the cycles `valid` is high, against a reference over directed and random stimulus.
I’ll inspect the existing package/wrapper and repo conventions first, then implement `rtl/sdiv.sv` in the same style and run the available compile/tests.
shell
rg --files
output
Chunk ID: 89b201
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Process exited with code 0
Original token count: 19
Output:
sdiv_core/rtl/sdiv.sv
sdiv_core/rtl/divp_pkg.sv
sdiv_core/rtl/sdiv_top.sv
shell
git status --short
output
Chunk ID: 33a42a
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Output:
/bin/bash: line 1: git: command not found
The workspace is a small RTL-only tree under `/work/sdiv_core`. `git` is not installed here, so I’ll rely on direct file inspection and local tool checks.
shell
sed -n '1,220p' rtl/sdiv.sv
output
Chunk ID: 880bbc
Wall time: 0.0000 seconds
Process exited with code 0
Original token count: 811
Output:
//==============================================================================
// sdiv.sv
//
// Multi-cycle signed integer divider with a start/busy/valid handshake.
//
// ---------------------------------------------------------------------------
//  >>> IMPLEMENTATION REQUIRED <<<
//
//  The module ports, parameters and a small set of state registers are
//  provided. The operand latch, the latency/handshake control and the signed
//  result are left as a TODO and currently drive constant zeros, so the divider
//  produces no useful result and the verifier FAILS.
//
//  Implement the behaviour described in instruction.md. Do NOT change the
//  module name, the port list, or the parameter list.
//
//  iverilog 11 note: a bit/part-select of an EXPRESSION (a sum, a shift, a
//  function-call result) is a syntax error under `iverilog -g2012`. Index only
//  named signals, and do any bit work that needs an intermediate value inside a
//  `function automatic` using named locals. Write negative full-scale constants
//  as bit patterns (e.g. 16'h8000 for -32768), not as -16'sd32768.
// ---------------------------------------------------------------------------
//==============================================================================
`timescale 1ns/1ps

module sdiv #(
    parameter W = 16,
    parameter N = 16
) (
    input  logic                  clk,
    input  logic                  rst_n,
    input  logic                  start,
    input  logic signed [W-1:0]   dividend,
    input  logic signed [W-1:0]   divisor,
    output logic signed [W-1:0]   quotient,
    output logic signed [W-1:0]   remainder,
    output logic                  busy,
    output logic                  valid
);

  // ---------------------------------------------------------------------------
  // State registers (provided). Latch the operands here on an accepted start and
  // track the in-flight progress with the counter.
  // ---------------------------------------------------------------------------
  logic signed [W-1:0] a_q;        // latched dividend
  logic signed [W-1:0] b_q;        // latched divisor
  logic        [7:0]   cnt;        // in-flight progress
  logic                run;        // a divide is in progress

  // ===========================================================================
  // TODO: IMPLEMENT THE DIVIDER.
  //   * accept a start only when not busy; latch dividend/divisor at that edge;
  //   * after the fixed latency, present the signed quotient/remainder and pulse
  //     valid for one clock, with busy and valid never overlapping;
  //   * asynchronous active-low reset clears all state and all outputs.
  //
  // The placeholder below keeps the module compilable but INCORRECT.
  // ===========================================================================
  always_ff @(posedge clk or negedge rst_n) begin
    if (!rst_n) begin
      a_q       <= '0;
      b_q       <= '0;
      cnt       <= 8'd0;
      run       <= 1'b0;
      busy      <= 1'b0;
      valid     <= 1'b0;
      quotient  <= '0;
      remainder <= '0;
    end else begin
      // TODO: replace with the real latch + latency control + result.
      run <= run;
      cnt <= cnt;
    end
  end

endmodule : sdiv
shell
sed -n '1,220p' rtl/divp_pkg.sv
output
Chunk ID: 707625
Wall time: 0.0000 seconds
Process exited with code 0
Original token count: 303
Output:
//==============================================================================
// divp_pkg.sv
//
// Shared geometry and constants for the multi-cycle signed divider. The block
// latches a signed dividend/divisor on an accepted start and produces a signed
// quotient/remainder after a fixed number of clocks, with a start/busy/valid
// handshake. Parameters are declared without an explicit data type for broad
// simulator compatibility (Icarus Verilog 11); they default to integer
// constants, which is sufficient here.
//
// DO NOT change this file.
//==============================================================================
`ifndef DIVP_PKG_SV
`define DIVP_PKG_SV

package divp_pkg;

  localparam W      = 16;       // operand / result word width (signed two's comp)
  localparam N      = 16;       // result latency: clocks from accept to valid

  // Defined divide-by-zero outputs (divisor == 0). Written as raw bit patterns
  // because the negative saturation value is the most-negative 16-bit number.
  localparam DIV0_Q_POS = 16'h7FFF;   //  32767, used when dividend >= 0
  localparam DIV0_Q_NEG = 16'h8000;   // -32768, used when dividend <  0

endpackage : divp_pkg

`endif // DIVP_PKG_SV
shell
sed -n '1,220p' rtl/sdiv_top.sv
output
Chunk ID: 3272be
Wall time: 0.0001 seconds
Process exited with code 0
Original token count: 346
Output:
//==============================================================================
// sdiv_top.sv
//
// Thin integration wrapper. The verification environment drives this wrapper so
// that the instantiation wiring is exercised alongside the divider itself. It
// instantiates sdiv with the project-default geometry from divp_pkg.
//
// DO NOT change this file.
//==============================================================================
`timescale 1ns/1ps
`include "divp_pkg.sv"

module sdiv_top (
    input  logic                          clk,
    input  logic                          rst_n,
    input  logic                          start,
    input  logic signed [divp_pkg::W-1:0] dividend,
    input  logic signed [divp_pkg::W-1:0] divisor,
    output logic signed [divp_pkg::W-1:0] quotient,
    output logic signed [divp_pkg::W-1:0] remainder,
    output logic                          busy,
    output logic                          valid
);

  // Bare instantiation: the divider carries its own default geometry, so a
  // submission needs no parameter override to elaborate correctly.
  sdiv u_sdiv (
      .clk       (clk),
      .rst_n     (rst_n),
      .start     (start),
      .dividend  (dividend),
      .divisor   (divisor),
      .quotient  (quotient),
      .remainder (remainder),
      .busy      (busy),
      .valid     (valid)
  );

endmodule : sdiv_top
shell
find . -maxdepth 3 -type f -print
output
Chunk ID: 1f0efb
Wall time: 0.0000 seconds
Process exited with code 0
Original token count: 13
Output:
./rtl/sdiv_top.sv
./rtl/divp_pkg.sv
./rtl/sdiv.sv
The existing module already has the intended state registers, so the implementation can stay compact: latch operands on an idle `start`, count a fixed 16-cycle window, and compute the floored result from the latched values on the result edge.
I’m going to replace the stub with registered control plus small helper functions for the defined divide cases and the floor-division correction. The helper functions avoid expression slicing and keep the sequential block focused on handshake timing.
apply_patch
*** Begin Patch
*** Update File: /work/sdiv_core/rtl/sdiv.sv
@@
   logic signed [W-1:0] a_q;        // latched dividend
   logic signed [W-1:0] b_q;        // latched divisor
   logic        [7:0]   cnt;        // in-flight progress
   logic                run;        // a divide is in progress
 
-  // ===========================================================================
-  // TODO: IMPLEMENT THE DIVIDER.
-  //   * accept a start only when not busy; latch dividend/divisor at that edge;
-  //   * after the fixed latency, present the signed quotient/remainder and pulse
-  //     valid for one clock, with busy and valid never overlapping;
-  //   * asynchronous active-low reset clears all state and all outputs.
-  //
-  // The placeholder below keeps the module compilable but INCORRECT.
-  // ===========================================================================
+  localparam logic signed [W-1:0] MIN_VALUE = {1'b1, {(W-1){1'b0}}};
+  localparam logic signed [W-1:0] MAX_VALUE = {1'b0, {(W-1){1'b1}}};
+  localparam logic signed [W-1:0] NEG_ONE   = {W{1'b1}};
+  localparam logic signed [W-1:0] ONE_VALUE = {{(W-1){1'b0}}, 1'b1};
+
+  function automatic logic signed [W-1:0] floor_quotient(
+      input logic signed [W-1:0] a,
+      input logic signed [W-1:0] b
+  );
+    logic signed [W-1:0] q_trunc;
+    logic signed [W-1:0] r_trunc;
+    begin
+      if (b == '0) begin
+        if (a[W-1]) begin
+          floor_quotient = MIN_VALUE;
+        end else begin
+          floor_quotient = MAX_VALUE;
+        end
+      end else if ((a == MIN_VALUE) && (b == NEG_ONE)) begin
+        floor_quotient = MAX_VALUE;
+      end else begin
+        q_trunc = a / b;
+        r_trunc = a % b;
+        if ((r_trunc != '0) && (a[W-1] ^ b[W-1])) begin
+          floor_quotient = q_trunc - ONE_VALUE;
+        end else begin
+          floor_quotient = q_trunc;
+        end
+      end
+    end
+  endfunction
+
+  function automatic logic signed [W-1:0] floor_remainder(
+      input logic signed [W-1:0] a,
+      input logic signed [W-1:0] b
+  );
+    logic signed [W-1:0] r_trunc;
+    begin
+      if (b == '0) begin
+        floor_remainder = a;
+      end else if ((a == MIN_VALUE) && (b == NEG_ONE)) begin
+        floor_remainder = '0;
+      end else begin
+        r_trunc = a % b;
+        if ((r_trunc != '0) && (a[W-1] ^ b[W-1])) begin
+          floor_remainder = r_trunc + b;
+        end else begin
+          floor_remainder = r_trunc;
+        end
+      end
+    end
+  endfunction
+
   always_ff @(posedge clk or negedge rst_n) begin
     if (!rst_n) begin
       a_q       <= '0;
       b_q       <= '0;
@@
       quotient  <= '0;
       remainder <= '0;
     end else begin
-      // TODO: replace with the real latch + latency control + result.
-      run <= run;
-      cnt <= cnt;
+      valid <= 1'b0;
+
+      if (run) begin
+        if (cnt == N[7:0]) begin
+          run       <= 1'b0;
+          cnt       <= 8'd0;
+          busy      <= 1'b0;
+          valid     <= 1'b1;
+          quotient  <= floor_quotient(a_q, b_q);
+          remainder <= floor_remainder(a_q, b_q);
+        end else begin
+          cnt  <= cnt + 8'd1;
+          busy <= 1'b1;
+        end
+      end else if (start) begin
+        a_q   <= dividend;
+        b_q   <= divisor;
+        cnt   <= 8'd1;
+        run   <= 1'b1;
+        busy  <= 1'b0;
+      end else begin
+        cnt  <= 8'd0;
+        busy <= 1'b0;
+      end
     end
   end
 
 endmodule : sdiv
*** End Patch


Exit code: 0
Wall time: 0 seconds
Output:
Success. Updated the following files:
M /work/sdiv_core/rtl/sdiv.sv
The first edit is in place. I noticed the counter comparison should avoid slicing the `N` parameter inline for Icarus compatibility, so I’ll tighten that before compiling.
apply_patch
*** Begin Patch
*** Update File: /work/sdiv_core/rtl/sdiv.sv
@@
   localparam logic signed [W-1:0] MIN_VALUE = {1'b1, {(W-1){1'b0}}};
   localparam logic signed [W-1:0] MAX_VALUE = {1'b0, {(W-1){1'b1}}};
   localparam logic signed [W-1:0] NEG_ONE   = {W{1'b1}};
   localparam logic signed [W-1:0] ONE_VALUE = {{(W-1){1'b0}}, 1'b1};
+  localparam logic        [7:0]   N_COUNT   = N;
@@
       valid <= 1'b0;
 
       if (run) begin
-        if (cnt == N[7:0]) begin
+        if (cnt == N_COUNT) begin
*** End Patch


Exit code: 0
Wall time: 0 seconds
Output:
Success. Updated the following files:
M /work/sdiv_core/rtl/sdiv.sv
Now I’ll run the RTL through `iverilog -g2012`. Since there’s no visible testbench, I’ll also create a temporary local checker outside the repo to exercise latency, ignore-while-busy, reset, and the sign quadrants.
shell
iverilog -g2012 -Wall -I rtl -o /tmp/sdiv_elab.vvp rtl/sdiv.sv rtl/sdiv_top.sv
output
Chunk ID: e5811f
Wall time: 0.0000 seconds
Process exited with code 0
Original token count: 35
Output:
rtl/divp_pkg.sv:16: warning: timescale for divp_pkg inherited from another file.
rtl/sdiv_top.sv:10: ...: The inherited timescale is here.
shell
sed -n '1,240p' rtl/sdiv.sv
output
Chunk ID: 8634b1
Wall time: 0.0000 seconds
Process exited with code 0
Original token count: 1202
Output:
//==============================================================================
// sdiv.sv
//
// Multi-cycle signed integer divider with a start/busy/valid handshake.
//
// ---------------------------------------------------------------------------
//  >>> IMPLEMENTATION REQUIRED <<<
//
//  The module ports, parameters and a small set of state registers are
//  provided. The operand latch, the latency/handshake control and the signed
//  result are left as a TODO and currently drive constant zeros, so the divider
//  produces no useful result and the verifier FAILS.
//
//  Implement the behaviour described in instruction.md. Do NOT change the
//  module name, the port list, or the parameter list.
//
//  iverilog 11 note: a bit/part-select of an EXPRESSION (a sum, a shift, a
//  function-call result) is a syntax error under `iverilog -g2012`. Index only
//  named signals, and do any bit work that needs an intermediate value inside a
//  `function automatic` using named locals. Write negative full-scale constants
//  as bit patterns (e.g. 16'h8000 for -32768), not as -16'sd32768.
// ---------------------------------------------------------------------------
//==============================================================================
`timescale 1ns/1ps

module sdiv #(
    parameter W = 16,
    parameter N = 16
) (
    input  logic                  clk,
    input  logic                  rst_n,
    input  logic                  start,
    input  logic signed [W-1:0]   dividend,
    input  logic signed [W-1:0]   divisor,
    output logic signed [W-1:0]   quotient,
    output logic signed [W-1:0]   remainder,
    output logic                  busy,
    output logic                  valid
);

  // ---------------------------------------------------------------------------
  // State registers (provided). Latch the operands here on an accepted start and
  // track the in-flight progress with the counter.
  // ---------------------------------------------------------------------------
  logic signed [W-1:0] a_q;        // latched dividend
  logic signed [W-1:0] b_q;        // latched divisor
  logic        [7:0]   cnt;        // in-flight progress
  logic                run;        // a divide is in progress

  localparam logic signed [W-1:0] MIN_VALUE = {1'b1, {(W-1){1'b0}}};
  localparam logic signed [W-1:0] MAX_VALUE = {1'b0, {(W-1){1'b1}}};
  localparam logic signed [W-1:0] NEG_ONE   = {W{1'b1}};
  localparam logic signed [W-1:0] ONE_VALUE = {{(W-1){1'b0}}, 1'b1};
  localparam logic        [7:0]   N_COUNT   = N;

  function automatic logic signed [W-1:0] floor_quotient(
      input logic signed [W-1:0] a,
      input logic signed [W-1:0] b
  );
    logic signed [W-1:0] q_trunc;
    logic signed [W-1:0] r_trunc;
    begin
      if (b == '0) begin
        if (a[W-1]) begin
          floor_quotient = MIN_VALUE;
        end else begin
          floor_quotient = MAX_VALUE;
        end
      end else if ((a == MIN_VALUE) && (b == NEG_ONE)) begin
        floor_quotient = MAX_VALUE;
      end else begin
        q_trunc = a / b;
        r_trunc = a % b;
        if ((r_trunc != '0) && (a[W-1] ^ b[W-1])) begin
          floor_quotient = q_trunc - ONE_VALUE;
        end else begin
          floor_quotient = q_trunc;
        end
      end
    end
  endfunction

  function automatic logic signed [W-1:0] floor_remainder(
      input logic signed [W-1:0] a,
      input logic signed [W-1:0] b
  );
    logic signed [W-1:0] r_trunc;
    begin
      if (b == '0) begin
        floor_remainder = a;
      end else if ((a == MIN_VALUE) && (b == NEG_ONE)) begin
        floor_remainder = '0;
      end else begin
        r_trunc = a % b;
        if ((r_trunc != '0) && (a[W-1] ^ b[W-1])) begin
          floor_remainder = r_trunc + b;
        end else begin
          floor_remainder = r_trunc;
        end
      end
    end
  endfunction

  always_ff @(posedge clk or negedge rst_n) begin
    if (!rst_n) begin
      a_q       <= '0;
      b_q       <= '0;
      cnt       <= 8'd0;
      run       <= 1'b0;
      busy      <= 1'b0;
      valid     <= 1'b0;
      quotient  <= '0;
      remainder <= '0;
    end else begin
      valid <= 1'b0;

      if (run) begin
        if (cnt == N_COUNT) begin
          run       <= 1'b0;
          cnt       <= 8'd0;
          busy      <= 1'b0;
          valid     <= 1'b1;
          quotient  <= floor_quotient(a_q, b_q);
          remainder <= floor_remainder(a_q, b_q);
        end else begin
          cnt  <= cnt + 8'd1;
          busy <= 1'b1;
        end
      end else if (start) begin
        a_q   <= dividend;
        b_q   <= divisor;
        cnt   <= 8'd1;
        run   <= 1'b1;
        busy  <= 1'b0;
      end else begin
        cnt  <= 8'd0;
        busy <= 1'b0;
      end
    end
  end

endmodule : sdiv
Elaboration passes under `iverilog -g2012`; the only warning is a pre-existing package timescale inheritance warning. I’m adding a throwaway testbench now to check the exact cycle timing and the special arithmetic cases.
apply_patch
*** Begin Patch
*** Add File: /work/sdiv_core/tmp_sdiv_tb.sv
+`timescale 1ns/1ps
+
+module tmp_sdiv_tb;
+  localparam int W = 16;
+  localparam int N = 16;
+
+  logic clk;
+  logic rst_n;
+  logic start;
+  logic signed [W-1:0] dividend;
+  logic signed [W-1:0] divisor;
+  logic signed [W-1:0] quotient;
+  logic signed [W-1:0] remainder;
+  logic busy;
+  logic valid;
+
+  int errors;
+
+  sdiv dut (
+      .clk(clk),
+      .rst_n(rst_n),
+      .start(start),
+      .dividend(dividend),
+      .divisor(divisor),
+      .quotient(quotient),
+      .remainder(remainder),
+      .busy(busy),
+      .valid(valid)
+  );
+
+  initial begin
+    clk = 1'b0;
+    forever #5 clk = ~clk;
+  end
+
+  function automatic logic signed [W-1:0] ref_q(
+      input logic signed [W-1:0] a,
+      input logic signed [W-1:0] b
+  );
+    integer ai;
+    integer bi;
+    integer qi;
+    integer ri;
+    begin
+      ai = a;
+      bi = b;
+      if (bi == 0) begin
+        qi = (ai < 0) ? -32768 : 32767;
+      end else if ((ai == -32768) && (bi == -1)) begin
+        qi = 32767;
+      end else begin
+        qi = ai / bi;
+        ri = ai % bi;
+        if ((ri != 0) && ((ai < 0) != (bi < 0))) begin
+          qi = qi - 1;
+        end
+      end
+      ref_q = qi[W-1:0];
+    end
+  endfunction
+
+  function automatic logic signed [W-1:0] ref_r(
+      input logic signed [W-1:0] a,
+      input logic signed [W-1:0] b
+  );
+    integer ai;
+    integer bi;
+    integer ri;
+    begin
+      ai = a;
+      bi = b;
+      if (bi == 0) begin
+        ri = ai;
+      end else if ((ai == -32768) && (bi == -1)) begin
+        ri = 0;
+      end else begin
+        ri = ai % bi;
+        if ((ri != 0) && ((ai < 0) != (bi < 0))) begin
+          ri = ri + bi;
+        end
+      end
+      ref_r = ri[W-1:0];
+    end
+  endfunction
+
+  task automatic check_div(
+      input logic signed [W-1:0] a,
+      input logic signed [W-1:0] b
+  );
+    int i;
+    begin
+      @(negedge clk);
+      dividend = a;
+      divisor = b;
+      start = 1'b1;
+      @(posedge clk);
+      #1;
+      if (busy !== 1'b0 || valid !== 1'b0) begin
+        $display("accept edge handshake mismatch a=%0d b=%0d busy=%0b valid=%0b", a, b, busy, valid);
+        errors++;
+      end
+      @(negedge clk);
+      start = 1'b0;
+      dividend = 16'sd12345;
+      divisor = -16'sd7;
+      for (i = 1; i < N; i++) begin
+        @(posedge clk);
+        #1;
+        if (busy !== 1'b1 || valid !== 1'b0) begin
+          $display("busy window mismatch i=%0d a=%0d b=%0d busy=%0b valid=%0b", i, a, b, busy, valid);
+          errors++;
+        end
+        if (i == 3) begin
+          @(negedge clk);
+          start = 1'b1;
+          dividend = -16'sd222;
+          divisor = 16'sd5;
+          @(negedge clk);
+          start = 1'b0;
+        end
+      end
+      @(posedge clk);
+      #1;
+      if (busy !== 1'b0 || valid !== 1'b1 || quotient !== ref_q(a, b) || remainder !== ref_r(a, b)) begin
+        $display("result mismatch a=%0d b=%0d busy=%0b valid=%0b q=%0d/%0d r=%0d/%0d",
+                 a, b, busy, valid, quotient, ref_q(a, b), remainder, ref_r(a, b));
+        errors++;
+      end
+      @(posedge clk);
+      #1;
+      if (valid !== 1'b0) begin
+        $display("valid held high a=%0d b=%0d", a, b);
+        errors++;
+      end
+    end
+  endtask
+
+  initial begin
+    errors = 0;
+    rst_n = 1'b0;
+    start = 1'b0;
+    dividend = '0;
+    divisor = '0;
+    #2;
+    if (busy !== 1'b0 || valid !== 1'b0 || quotient !== '0 || remainder !== '0) begin
+      $display("async reset output mismatch");
+      errors++;
+    end
+    repeat (2) @(posedge clk);
+    @(negedge clk);
+    rst_n = 1'b1;
+
+    check_div(16'sd7, 16'sd3);
+    check_div(-16'sd7, 16'sd3);
+    check_div(16'sd7, -16'sd3);
+    check_div(-16'sd7, -16'sd3);
+    check_div(16'sd7, 16'sd0);
+    check_div(-16'sd7, 16'sd0);
+    check_div(16'h8000, -16'sd1);
+    check_div(16'h8000, 16'sd32767);
+
+    if (errors == 0) begin
+      $display("PASS");
+    end else begin
+      $display("FAIL errors=%0d", errors);
+    end
+    $finish;
+  end
+endmodule
*** End Patch


Exit code: 0
Wall time: 0 seconds
Output:
Success. Updated the following files:
A /work/sdiv_core/tmp_sdiv_tb.sv
The temporary checker is in place and will be removed after use. It mutates the input operands during the busy window to make sure the result comes only from the accepted operands.
shell
iverilog -g2012 -Wall -I rtl -o /tmp/sdiv_tb.vvp rtl/sdiv.sv tmp_sdiv_tb.sv && vvp /tmp/sdiv_tb.vvp
output
Chunk ID: 07a383
Wall time: 0.0000 seconds
Process exited with code 0
Original token count: 226
Output:
busy window mismatch i=15 a=7 b=3 busy=0 valid=1
result mismatch a=7 b=3 busy=0 valid=0 q=2/2 r=1/1
busy window mismatch i=15 a=-7 b=3 busy=0 valid=1
result mismatch a=-7 b=3 busy=0 valid=0 q=-3/-3 r=2/2
busy window mismatch i=15 a=7 b=-3 busy=0 valid=1
result mismatch a=7 b=-3 busy=0 valid=0 q=-3/-3 r=-2/-2
busy window mismatch i=15 a=-7 b=-3 busy=0 valid=1
result mismatch a=-7 b=-3 busy=0 valid=0 q=2/2 r=-1/-1
busy window mismatch i=15 a=7 b=0 busy=0 valid=1
result mismatch a=7 b=0 busy=0 valid=0 q=32767/32767 r=7/7
busy window mismatch i=15 a=-7 b=0 busy=0 valid=1
result mismatch a=-7 b=0 busy=0 valid=0 q=-32768/-32768 r=-7/-7
busy window mismatch i=15 a=-32768 b=-1 busy=0 valid=1
result mismatch a=-32768 b=-1 busy=0 valid=0 q=32767/32767 r=0/0
busy window mismatch i=15 a=-32768 b=32767 busy=0 valid=1
result mismatch a=-32768 b=32767 busy=0 valid=0 q=-2/-2 r=32766/32766
FAIL errors=16
The first checker had a flaw: its injected busy-window start pulse consumed a clock from the checking loop, so it expected the result one cycle late. I’ll fix the temporary checker and rerun; the RTL timing itself is still consistent with the intended counter schedule.
apply_patch
*** Begin Patch
*** Update File: /work/sdiv_core/tmp_sdiv_tb.sv
@@
       @(posedge clk);
       #1;
       if (busy !== 1'b0 || valid !== 1'b0) begin
         $display("accept edge handshake mismatch a=%0d b=%0d busy=%0b valid=%0b", a, b, busy, valid);
         errors++;
       end
-      @(negedge clk);
-      start = 1'b0;
-      dividend = 16'sd12345;
-      divisor = -16'sd7;
-      for (i = 1; i < N; i++) begin
+      for (i = 1; i <= N; i++) begin
+        @(negedge clk);
+        if (i == 1) begin
+          start = 1'b1;
+          dividend = -16'sd222;
+          divisor = 16'sd5;
+        end else begin
+          start = 1'b0;
+          dividend = 16'sd12345;
+          divisor = -16'sd7;
+        end
         @(posedge clk);
         #1;
-        if (busy !== 1'b1 || valid !== 1'b0) begin
-          $display("busy window mismatch i=%0d a=%0d b=%0d busy=%0b valid=%0b", i, a, b, busy, valid);
-          errors++;
-        end
-        if (i == 3) begin
-          @(negedge clk);
-          start = 1'b1;
-          dividend = -16'sd222;
-          divisor = 16'sd5;
-          @(negedge clk);
-          start = 1'b0;
+        if (i < N) begin
+          if (busy !== 1'b1 || valid !== 1'b0) begin
+            $display("busy window mismatch i=%0d a=%0d b=%0d busy=%0b valid=%0b", i, a, b, busy, valid);
+            errors++;
+          end
+        end else begin
+          if (busy !== 1'b0 || valid !== 1'b1 || quotient !== ref_q(a, b) || remainder !== ref_r(a, b)) begin
+            $display("result mismatch a=%0d b=%0d busy=%0b valid=%0b q=%0d/%0d r=%0d/%0d",
+                     a, b, busy, valid, quotient, ref_q(a, b), remainder, ref_r(a, b));
+            errors++;
+          end
         end
       end
-      @(posedge clk);
-      #1;
-      if (busy !== 1'b0 || valid !== 1'b1 || quotient !== ref_q(a, b) || remainder !== ref_r(a, b)) begin
-        $display("result mismatch a=%0d b=%0d busy=%0b valid=%0b q=%0d/%0d r=%0d/%0d",
-                 a, b, busy, valid, quotient, ref_q(a, b), remainder, ref_r(a, b));
-        errors++;
-      end
       @(posedge clk);
       #1;
       if (valid !== 1'b0) begin
*** End Patch


Exit code: 0
Wall time: 0 seconds
Output:
Success. Updated the following files:
M /work/sdiv_core/tmp_sdiv_tb.sv
The checker now observes every clock in the latency window while still holding a bogus `start` during the first busy cycle. I’ll rerun it.
shell
iverilog -g2012 -Wall -I rtl -o /tmp/sdiv_tb.vvp rtl/sdiv.sv tmp_sdiv_tb.sv && vvp /tmp/sdiv_tb.vvp
output
Chunk ID: e50745
Wall time: 0.0000 seconds
Process exited with code 0
Original token count: 2
Output:
PASS
The corrected local checker passes the directed cases, including operand mutation while busy. I’ll remove the temporary testbench and do one final elaboration using the wrapper ordering a grader is likely to use.
apply_patch
*** Begin Patch
*** Delete File: /work/sdiv_core/tmp_sdiv_tb.sv
*** End Patch


Exit code: 0
Wall time: 0 seconds
Output:
Success. Updated the following files:
D /work/sdiv_core/tmp_sdiv_tb.sv
shell
iverilog -g2012 -Wall -I rtl -o /tmp/sdiv_elab_topfirst.vvp rtl/sdiv_top.sv rtl/sdiv.sv
output
Chunk ID: 2690be
Wall time: 0.0000 seconds
Process exited with code 0
Original token count: 35
Output:
rtl/divp_pkg.sv:16: warning: timescale for divp_pkg inherited from another file.
rtl/sdiv_top.sv:10: ...: The inherited timescale is here.
shell
find . -maxdepth 2 -type f -print
output
Chunk ID: 4b65c8
Wall time: 0.0000 seconds
Process exited with code 0
Original token count: 13
Output:
./rtl/sdiv_top.sv
./rtl/divp_pkg.sv
./rtl/sdiv.sv
shell
nl -ba rtl/sdiv.sv | sed -n '1,220p'
output
Chunk ID: 0bef71
Wall time: 0.0000 seconds
Process exited with code 0
Original token count: 1450
Output:
     1	//==============================================================================
     2	// sdiv.sv
     3	//
     4	// Multi-cycle signed integer divider with a start/busy/valid handshake.
     5	//
     6	// ---------------------------------------------------------------------------
     7	//  >>> IMPLEMENTATION REQUIRED <<<
     8	//
     9	//  The module ports, parameters and a small set of state registers are
    10	//  provided. The operand latch, the latency/handshake control and the signed
    11	//  result are left as a TODO and currently drive constant zeros, so the divider
    12	//  produces no useful result and the verifier FAILS.
    13	//
    14	//  Implement the behaviour described in instruction.md. Do NOT change the
    15	//  module name, the port list, or the parameter list.
    16	//
    17	//  iverilog 11 note: a bit/part-select of an EXPRESSION (a sum, a shift, a
    18	//  function-call result) is a syntax error under `iverilog -g2012`. Index only
    19	//  named signals, and do any bit work that needs an intermediate value inside a
    20	//  `function automatic` using named locals. Write negative full-scale constants
    21	//  as bit patterns (e.g. 16'h8000 for -32768), not as -16'sd32768.
    22	// ---------------------------------------------------------------------------
    23	//==============================================================================
    24	`timescale 1ns/1ps
    25	
    26	module sdiv #(
    27	    parameter W = 16,
    28	    parameter N = 16
    29	) (
    30	    input  logic                  clk,
    31	    input  logic                  rst_n,
    32	    input  logic                  start,
    33	    input  logic signed [W-1:0]   dividend,
    34	    input  logic signed [W-1:0]   divisor,
    35	    output logic signed [W-1:0]   quotient,
    36	    output logic signed [W-1:0]   remainder,
    37	    output logic                  busy,
    38	    output logic                  valid
    39	);
    40	
    41	  // ---------------------------------------------------------------------------
    42	  // State registers (provided). Latch the operands here on an accepted start and
    43	  // track the in-flight progress with the counter.
    44	  // ---------------------------------------------------------------------------
    45	  logic signed [W-1:0] a_q;        // latched dividend
    46	  logic signed [W-1:0] b_q;        // latched divisor
    47	  logic        [7:0]   cnt;        // in-flight progress
    48	  logic                run;        // a divide is in progress
    49	
    50	  localparam logic signed [W-1:0] MIN_VALUE = {1'b1, {(W-1){1'b0}}};
    51	  localparam logic signed [W-1:0] MAX_VALUE = {1'b0, {(W-1){1'b1}}};
    52	  localparam logic signed [W-1:0] NEG_ONE   = {W{1'b1}};
    53	  localparam logic signed [W-1:0] ONE_VALUE = {{(W-1){1'b0}}, 1'b1};
    54	  localparam logic        [7:0]   N_COUNT   = N;
    55	
    56	  function automatic logic signed [W-1:0] floor_quotient(
    57	      input logic signed [W-1:0] a,
    58	      input logic signed [W-1:0] b
    59	  );
    60	    logic signed [W-1:0] q_trunc;
    61	    logic signed [W-1:0] r_trunc;
    62	    begin
    63	      if (b == '0) begin
    64	        if (a[W-1]) begin
    65	          floor_quotient = MIN_VALUE;
    66	        end else begin
    67	          floor_quotient = MAX_VALUE;
    68	        end
    69	      end else if ((a == MIN_VALUE) && (b == NEG_ONE)) begin
    70	        floor_quotient = MAX_VALUE;
    71	      end else begin
    72	        q_trunc = a / b;
    73	        r_trunc = a % b;
    74	        if ((r_trunc != '0) && (a[W-1] ^ b[W-1])) begin
    75	          floor_quotient = q_trunc - ONE_VALUE;
    76	        end else begin
    77	          floor_quotient = q_trunc;
    78	        end
    79	      end
    80	    end
    81	  endfunction
    82	
    83	  function automatic logic signed [W-1:0] floor_remainder(
    84	      input logic signed [W-1:0] a,
    85	      input logic signed [W-1:0] b
    86	  );
    87	    logic signed [W-1:0] r_trunc;
    88	    begin
    89	      if (b == '0) begin
    90	        floor_remainder = a;
    91	      end else if ((a == MIN_VALUE) && (b == NEG_ONE)) begin
    92	        floor_remainder = '0;
    93	      end else begin
    94	        r_trunc = a % b;
    95	        if ((r_trunc != '0) && (a[W-1] ^ b[W-1])) begin
    96	          floor_remainder = r_trunc + b;
    97	        end else begin
    98	          floor_remainder = r_trunc;
    99	        end
   100	      end
   101	    end
   102	  endfunction
   103	
   104	  always_ff @(posedge clk or negedge rst_n) begin
   105	    if (!rst_n) begin
   106	      a_q       <= '0;
   107	      b_q       <= '0;
   108	      cnt       <= 8'd0;
   109	      run       <= 1'b0;
   110	      busy      <= 1'b0;
   111	      valid     <= 1'b0;
   112	      quotient  <= '0;
   113	      remainder <= '0;
   114	    end else begin
   115	      valid <= 1'b0;
   116	
   117	      if (run) begin
   118	        if (cnt == N_COUNT) begin
   119	          run       <= 1'b0;
   120	          cnt       <= 8'd0;
   121	          busy      <= 1'b0;
   122	          valid     <= 1'b1;
   123	          quotient  <= floor_quotient(a_q, b_q);
   124	          remainder <= floor_remainder(a_q, b_q);
   125	        end else begin
   126	          cnt  <= cnt + 8'd1;
   127	          busy <= 1'b1;
   128	        end
   129	      end else if (start) begin
   130	        a_q   <= dividend;
   131	        b_q   <= divisor;
   132	        cnt   <= 8'd1;
   133	        run   <= 1'b1;
   134	        busy  <= 1'b0;
   135	      end else begin
   136	        cnt  <= 8'd0;
   137	        busy <= 1'b0;
   138	      end
   139	    end
   140	  end
   141	
   142	endmodule : sdiv
The final wrapper-first elaboration also passes, with the same package timescale warning. I’m cleaning up the stale stub comments in `sdiv.sv` so the file no longer describes itself as a placeholder.
apply_patch
*** Begin Patch
*** Update File: /work/sdiv_core/rtl/sdiv.sv
@@
-//  >>> IMPLEMENTATION REQUIRED <<<
-//
-//  The module ports, parameters and a small set of state registers are
-//  provided. The operand latch, the latency/handshake control and the signed
-//  result are left as a TODO and currently drive constant zeros, so the divider
-//  produces no useful result and the verifier FAILS.
-//
-//  Implement the behaviour described in instruction.md. Do NOT change the
-//  module name, the port list, or the parameter list.
-//
 //  iverilog 11 note: a bit/part-select of an EXPRESSION (a sum, a shift, a
 //  function-call result) is a syntax error under `iverilog -g2012`. Index only
 //  named signals, and do any bit work that needs an intermediate value inside a
*** End Patch


Exit code: 0
Wall time: 0 seconds
Output:
Success. Updated the following files:
M /work/sdiv_core/rtl/sdiv.sv
The comments are cleaned up. I’ll run one last compile after that small edit.
shell
iverilog -g2012 -Wall -I rtl -o /tmp/sdiv_elab_final.vvp rtl/sdiv_top.sv rtl/sdiv.sv
output
Chunk ID: d951bb
Wall time: 0.0000 seconds
Process exited with code 0
Original token count: 35
Output:
rtl/divp_pkg.sv:16: warning: timescale for divp_pkg inherited from another file.
rtl/sdiv_top.sv:10: ...: The inherited timescale is here.
Implemented `rtl/sdiv.sv` with: - Registered operand capture on accepted `start` - Fixed `N=16` cycle latency - `busy` high only during in-flight cycles, never overlapping `valid` - One-cycle `valid` pulse with registered result outputs - Floored signed division correction - Defined divide-by-zero and `-32768 / -1` saturation behavior - Async active-low reset clearing state and outputs Verified with: ```bash iverilog -g2012 -Wall -I rtl -o /tmp/sdiv_elab_final.vvp rtl/sdiv_top.sv rtl/sdiv.sv ``` It elaborates successfully. The only warning is the existing `divp_pkg.sv` timescale inheritance warning.
Final diff , what the agent changed

No file changes, the agent left the workspace untouched.

Reproduce this trial: git checkout 2f94510 && PYTHONPATH=src python3 scripts/build_site.py , then open trial/trial_f431ac01bdbb48be. Re-running the agent live requires EVAL_PLATFORM_ENABLE_OAUTH_SMOKE=1 and is non-deterministic.

Trial trial_f431ac01bdbb48be · verifier authoritative; classifier explanatory.