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
EvidenceAgent's implementation (step 15, trajectory) fails to handle back-to-back re-arm correctly. The FSM only accepts a new `start` when `run==0` (idle), but the specification (instruction.md, 'Back-to-back divides' section) requires that a new divide be accepted when `start` is high on the result cycle (when `valid` pulses). The agent's local testbench (step 29) does not verify back-to-back re-arm on the valid cycle, only ignoring starts while busy mid-operation. Result is 'fail' (reward=0.0) in verifier/test-stdout.txt.
Root causeThe agent implemented operand capture and latency control but failed to recognize that the accept condition must include the result cycle (when cnt==N and busy==0). The FSM structure treats the result cycle as a terminal state, preventing simultaneous capture of fresh operands and presentation of the prior result. Back-to-back re-arm, which is a core requirement of the handshake, cannot work with this design.
RecommendationN/A - task is fine. The specification clearly describes the back-to-back re-arm requirement. The agent needed to either (a) recognize that the result cycle is a free cycle and should re-arm if start is asserted, or (b) use a design pattern that separates the operand-capture path from the result-delivery path. The fix would require restructuring the FSM to check for start during the result cycle: `if (run && cnt == N && start) begin capture new operands and latch result end else if (run && cnt == N) begin latch result only end`.
Trajectory
Tool-by-tool agent trajectory
23 tool calls · 2 tool types · 42 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 and wrapper first so the implementation matches the repo’s exact names and style before editing `rtl/sdiv.sv`.
shell
rg --files
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Chunk ID: 38b04f
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Output:
sdiv_core/rtl/sdiv.sv
sdiv_core/rtl/divp_pkg.sv
sdiv_core/rtl/sdiv_top.sv
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sed -n '1,220p' rtl/sdiv.sv
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Output:
sed: can't read rtl/sdiv.sv: No such file or directory
shell
rg -n "package|parameter|module sdiv|sdiv" -S .
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Chunk ID: e7f3b4
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Output:
./sdiv_core/rtl/sdiv_top.sv:2:// sdiv_top.sv
./sdiv_core/rtl/sdiv_top.sv:6:// instantiates sdiv with the project-default geometry from divp_pkg.
./sdiv_core/rtl/sdiv_top.sv:13:module sdiv_top (
./sdiv_core/rtl/sdiv_top.sv:26:  // submission needs no parameter override to elaborate correctly.
./sdiv_core/rtl/sdiv_top.sv:27:  sdiv u_sdiv (
./sdiv_core/rtl/sdiv_top.sv:39:endmodule : sdiv_top
./sdiv_core/rtl/divp_pkg.sv:7:// handshake. Parameters are declared without an explicit data type for broad
./sdiv_core/rtl/divp_pkg.sv:16:package divp_pkg;
./sdiv_core/rtl/divp_pkg.sv:26:endpackage : divp_pkg
./sdiv_core/rtl/sdiv.sv:2:// sdiv.sv
./sdiv_core/rtl/sdiv.sv:9://  The module ports, parameters and a small set of state registers are
./sdiv_core/rtl/sdiv.sv:15://  module name, the port list, or the parameter list.
./sdiv_core/rtl/sdiv.sv:26:module sdiv #(
./sdiv_core/rtl/sdiv.sv:27:    parameter W = 16,
./sdiv_core/rtl/sdiv.sv:28:    parameter N = 16
./sdiv_core/rtl/sdiv.sv:76:endmodule : sdiv
The files live under `sdiv_core/rtl`, not `/work/rtl`. I found the stub and am reading the package/top wrapper now, then I’ll patch the divider in place.
shell
sed -n '1,220p' sdiv_core/rtl/sdiv.sv
output
Chunk ID: eed5fa
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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 '1,180p' sdiv_core/rtl/divp_pkg.sv
output
Chunk ID: 7e7f4e
Wall time: 0.0000 seconds
Process exited with code 0
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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 '1,180p' sdiv_core/rtl/sdiv_top.sv
output
Chunk ID: bb6684
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Process exited with code 0
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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 /work -maxdepth 3 -type f | sort
output
Chunk ID: 6525d5
Wall time: 0.0000 seconds
Process exited with code 0
Original token count: 23
Output:
/work/sdiv_core/rtl/divp_pkg.sv
/work/sdiv_core/rtl/sdiv.sv
/work/sdiv_core/rtl/sdiv_top.sv
The stub already has operand and progress registers. I’m going to keep the implementation tightly scoped: latch accepted operands, count the fixed 16-cycle latency, and compute the floored signed result from the latched values only on the result edge.
I’m applying the implementation now. The result correction uses Verilog’s truncating quotient/remainder as an intermediate, then adjusts only when signs differ and the truncating remainder is nonzero.
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.
-  // ===========================================================================
+  logic        [2*W-1:0] result_w;
+  logic signed [W-1:0]   result_q;
+  logic signed [W-1:0]   result_r;
+
+  function automatic logic [2*W-1:0] floor_div_result;
+    input logic signed [W-1:0] a;
+    input logic signed [W-1:0] b;
+
+    logic signed [W-1:0] q_tmp;
+    logic signed [W-1:0] r_tmp;
+    logic signed [W-1:0] min_int;
+    logic signed [W-1:0] max_int;
+    logic signed [W-1:0] neg_one;
+    begin
+      min_int = {1'b1, {(W-1){1'b0}}};
+      max_int = {1'b0, {(W-1){1'b1}}};
+      neg_one = {W{1'b1}};
+
+      if (b == '0) begin
+        if (a[W-1]) begin
+          q_tmp = min_int;
+        end else begin
+          q_tmp = max_int;
+        end
+        r_tmp = a;
+      end else if ((a == min_int) && (b == neg_one)) begin
+        q_tmp = max_int;
+        r_tmp = '0;
+      end else begin
+        q_tmp = a / b;
+        r_tmp = a % b;
+
+        if ((r_tmp != '0) && (a[W-1] ^ b[W-1])) begin
+          q_tmp = q_tmp - {{(W-1){1'b0}}, 1'b1};
+          r_tmp = r_tmp + b;
+        end
+      end
+
+      floor_div_result = {q_tmp, r_tmp};
+    end
+  endfunction
+
+  always_comb begin
+    result_w = floor_div_result(a_q, b_q);
+    result_q = result_w[2*W-1:W];
+    result_r = result_w[W-1:0];
+  end
+
   always_ff @(posedge clk or negedge rst_n) begin
     if (!rst_n) begin
       a_q       <= '0;
       b_q       <= '0;
       cnt       <= 8'd0;
@@
       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) begin
+          run       <= 1'b0;
+          cnt       <= 8'd0;
+          busy      <= 1'b0;
+          valid     <= 1'b1;
+          quotient  <= result_q;
+          remainder <= result_r;
+        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
+        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 divider is patched. I’m compiling it with Icarus now, then I’ll run a small behavioral test for latency, ignored starts, reset behavior, and the signed division corner cases.
shell
iverilog -g2012 -o /tmp/sdiv_compile.vvp sdiv_core/rtl/sdiv_top.sv sdiv_core/rtl/sdiv.sv
output
Chunk ID: a4106a
Wall time: 0.0000 seconds
Process exited with code 1
Original token count: 27
Output:
sdiv_core/rtl/sdiv_top.sv:12: Include file divp_pkg.sv not found
No top level modules, and no -s option.
shell
nl -ba sdiv_core/rtl/sdiv.sv | sed -n '1,180p'
output
Chunk ID: 25fc5a
Wall time: 0.0000 seconds
Process exited with code 0
Original token count: 1313
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	  logic        [2*W-1:0] result_w;
    51	  logic signed [W-1:0]   result_q;
    52	  logic signed [W-1:0]   result_r;
    53	
    54	  function automatic logic [2*W-1:0] floor_div_result;
    55	    input logic signed [W-1:0] a;
    56	    input logic signed [W-1:0] b;
    57	
    58	    logic signed [W-1:0] q_tmp;
    59	    logic signed [W-1:0] r_tmp;
    60	    logic signed [W-1:0] min_int;
    61	    logic signed [W-1:0] max_int;
    62	    logic signed [W-1:0] neg_one;
    63	    begin
    64	      min_int = {1'b1, {(W-1){1'b0}}};
    65	      max_int = {1'b0, {(W-1){1'b1}}};
    66	      neg_one = {W{1'b1}};
    67	
    68	      if (b == '0) begin
    69	        if (a[W-1]) begin
    70	          q_tmp = min_int;
    71	        end else begin
    72	          q_tmp = max_int;
    73	        end
    74	        r_tmp = a;
    75	      end else if ((a == min_int) && (b == neg_one)) begin
    76	        q_tmp = max_int;
    77	        r_tmp = '0;
    78	      end else begin
    79	        q_tmp = a / b;
    80	        r_tmp = a % b;
    81	
    82	        if ((r_tmp != '0) && (a[W-1] ^ b[W-1])) begin
    83	          q_tmp = q_tmp - {{(W-1){1'b0}}, 1'b1};
    84	          r_tmp = r_tmp + b;
    85	        end
    86	      end
    87	
    88	      floor_div_result = {q_tmp, r_tmp};
    89	    end
    90	  endfunction
    91	
    92	  always_comb begin
    93	    result_w = floor_div_result(a_q, b_q);
    94	    result_q = result_w[2*W-1:W];
    95	    result_r = result_w[W-1:0];
    96	  end
    97	
    98	  always_ff @(posedge clk or negedge rst_n) begin
    99	    if (!rst_n) begin
   100	      a_q       <= '0;
   101	      b_q       <= '0;
   102	      cnt       <= 8'd0;
   103	      run       <= 1'b0;
   104	      busy      <= 1'b0;
   105	      valid     <= 1'b0;
   106	      quotient  <= '0;
   107	      remainder <= '0;
   108	    end else begin
   109	      valid <= 1'b0;
   110	
   111	      if (run) begin
   112	        if (cnt == N) begin
   113	          run       <= 1'b0;
   114	          cnt       <= 8'd0;
   115	          busy      <= 1'b0;
   116	          valid     <= 1'b1;
   117	          quotient  <= result_q;
   118	          remainder <= result_r;
   119	        end else begin
   120	          cnt  <= cnt + 8'd1;
   121	          busy <= 1'b1;
   122	        end
   123	      end else if (start) begin
   124	        a_q   <= dividend;
   125	        b_q   <= divisor;
   126	        cnt   <= 8'd1;
   127	        run   <= 1'b1;
   128	        busy  <= 1'b0;
   129	      end else begin
   130	        busy <= 1'b0;
   131	      end
   132	    end
   133	  end
   134	
   135	endmodule : sdiv
The first compile only failed because `sdiv_top.sv` includes the package by local include path; I’m rerunning with the RTL directory on the include path.
shell
iverilog -g2012 -I sdiv_core/rtl -o /tmp/sdiv_compile.vvp sdiv_core/rtl/sdiv_top.sv sdiv_core/rtl/sdiv.sv
output
Chunk ID: e355ee
Wall time: 0.0000 seconds
Process exited with code 2
Original token count: 26
Output:
sdiv_core/rtl/sdiv.sv:55: syntax error
sdiv_core/rtl/sdiv.sv:54: error: Syntax error defining function.
Icarus 11 is rejecting the newer typed function syntax. I’m switching that function to the older SystemVerilog-compatible form that this tool accepts.
apply_patch
*** Begin Patch
*** Update File: /work/sdiv_core/rtl/sdiv.sv
@@
-  function automatic logic [2*W-1:0] floor_div_result;
-    input logic signed [W-1:0] a;
-    input logic signed [W-1:0] b;
+  function automatic [2*W-1:0] floor_div_result;
+    input signed [W-1:0] a;
+    input signed [W-1:0] b;
 
-    logic signed [W-1:0] q_tmp;
-    logic signed [W-1:0] r_tmp;
-    logic signed [W-1:0] min_int;
-    logic signed [W-1:0] max_int;
-    logic signed [W-1:0] neg_one;
+    reg signed [W-1:0] q_tmp;
+    reg signed [W-1:0] r_tmp;
+    reg signed [W-1:0] min_int;
+    reg signed [W-1:0] max_int;
+    reg signed [W-1:0] neg_one;
*** End Patch


Exit code: 0
Wall time: 0 seconds
Output:
Success. Updated the following files:
M /work/sdiv_core/rtl/sdiv.sv
The syntax fix is in. I’m compiling again and then I’ll exercise the handshake with a local testbench.
shell
iverilog -g2012 -I sdiv_core/rtl -o /tmp/sdiv_compile.vvp sdiv_core/rtl/sdiv_top.sv sdiv_core/rtl/sdiv.sv
output
Chunk ID: 703518
Wall time: 0.0000 seconds
Process exited with code 0
Original token count: 129
Output:
sdiv_core/rtl/sdiv.sv:92: sorry: constant selects in always_* processes are not currently supported (all bits will be included).
sdiv_core/rtl/sdiv.sv:92: sorry: constant selects in always_* processes are not currently supported (all bits will be included).
sdiv_core/rtl/sdiv.sv:92: sorry: constant selects in always_* processes are not currently supported (all bits will be included).
sdiv_core/rtl/sdiv.sv:92: sorry: constant selects in always_* processes are not currently supported (all bits will be included).
It elaborates, but Icarus emits warnings for part-selects inside `always_comb`. I’m moving those to continuous assignments to keep the compile clean under the grader’s toolchain.
apply_patch
*** Begin Patch
*** Update File: /work/sdiv_core/rtl/sdiv.sv
@@
-  always_comb begin
-    result_w = floor_div_result(a_q, b_q);
-    result_q = result_w[2*W-1:W];
-    result_r = result_w[W-1:0];
-  end
+  assign result_w = floor_div_result(a_q, b_q);
+  assign result_q = result_w[2*W-1:W];
+  assign result_r = result_w[W-1:0];
*** End Patch


Exit code: 0
Wall time: 0 seconds
Output:
Success. Updated the following files:
M /work/sdiv_core/rtl/sdiv.sv
That cleanup is applied. I’m running a clean compile and a focused simulation now.
shell
iverilog -g2012 -I sdiv_core/rtl -o /tmp/sdiv_compile.vvp sdiv_core/rtl/sdiv_top.sv sdiv_core/rtl/sdiv.sv
output
Chunk ID: c55934
Wall time: 0.0000 seconds
Process exited with code 0
Original token count: 0
Output:
apply_patch
*** Begin Patch
*** Add File: /tmp/sdiv_tb.sv
+`timescale 1ns/1ps
+
+module tb;
+  localparam W = 16;
+  localparam N = 16;
+
+  logic clk = 1'b0;
+  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;
+
+  always #5 clk = ~clk;
+
+  sdiv dut (
+      .clk       (clk),
+      .rst_n     (rst_n),
+      .start     (start),
+      .dividend  (dividend),
+      .divisor   (divisor),
+      .quotient  (quotient),
+      .remainder (remainder),
+      .busy      (busy),
+      .valid     (valid)
+  );
+
+  task automatic fail(input string msg);
+    begin
+      $display("FAIL: %s at t=%0t", msg, $time);
+      $finish;
+    end
+  endtask
+
+  task automatic check_div(
+      input signed [W-1:0] a,
+      input signed [W-1:0] b,
+      input signed [W-1:0] exp_q,
+      input signed [W-1:0] exp_r
+  );
+    integer i;
+    begin
+      @(negedge clk);
+      dividend = a;
+      divisor  = b;
+      start    = 1'b1;
+
+      @(posedge clk);
+      #1;
+      if (busy !== 1'b0) fail("busy asserted on accept edge");
+      if (valid !== 1'b0) fail("valid asserted on accept edge");
+      start    = 1'b0;
+      dividend = 16'sd1234;
+      divisor  = -16'sd11;
+
+      for (i = 1; i < N; i = i + 1) begin
+        @(negedge clk);
+        if (i == 3) begin
+          start    = 1'b1;
+          dividend = 16'sd55;
+          divisor  = 16'sd5;
+        end else begin
+          start = 1'b0;
+        end
+
+        @(posedge clk);
+        #1;
+        if (busy !== 1'b1) fail("busy low during in-flight window");
+        if (valid !== 1'b0) fail("valid asserted before result edge");
+      end
+
+      @(negedge clk);
+      start = 1'b0;
+      @(posedge clk);
+      #1;
+      if (busy !== 1'b0) fail("busy overlapped result edge");
+      if (valid !== 1'b1) fail("valid missing on result edge");
+      if (quotient !== exp_q) fail("quotient mismatch");
+      if (remainder !== exp_r) fail("remainder mismatch");
+
+      @(posedge clk);
+      #1;
+      if (valid !== 1'b0) fail("valid wider than one cycle");
+    end
+  endtask
+
+  initial begin
+    rst_n    = 1'b0;
+    start    = 1'b0;
+    dividend = '0;
+    divisor  = '0;
+
+    #2;
+    if (busy !== 1'b0 || valid !== 1'b0 || quotient !== '0 || remainder !== '0) begin
+      fail("async reset did not clear outputs");
+    end
+
+    repeat (2) @(posedge clk);
+    rst_n = 1'b1;
+
+    check_div( 16'sd7,      16'sd3,  16'sd2,     16'sd1);
+    check_div(-16'sd7,      16'sd3, -16'sd3,     16'sd2);
+    check_div( 16'sd7,     -16'sd3, -16'sd3,    -16'sd2);
+    check_div(-16'sd7,     -16'sd3,  16'sd2,    -16'sd1);
+    check_div( 16'sd9,      16'sd0, 16'sh7fff,   16'sd9);
+    check_div(-16'sd9,      16'sd0, 16'sh8000,  -16'sd9);
+    check_div( 16'sh8000,  -16'sd1, 16'sh7fff,   16'sd0);
+
+    $display("PASS");
+    $finish;
+  end
+endmodule
*** End Patch


Exit code: 0
Wall time: 0 seconds
Output:
Success. Updated the following files:
A /tmp/sdiv_tb.sv
The local testbench is ready. I’m compiling and running it against the patched RTL.
shell
iverilog -g2012 -I sdiv_core/rtl -o /tmp/sdiv_tb.vvp /tmp/sdiv_tb.sv sdiv_core/rtl/sdiv.sv && vvp /tmp/sdiv_tb.vvp
output
Chunk ID: 1fde37
Wall time: 0.0000 seconds
Process exited with code 0
Original token count: 2
Output:
PASS
The directed simulation passes. I’m adding a lightweight randomized simulation pass as well because the sign rule is the risky part of this block.
apply_patch
*** Begin Patch
*** Update File: /tmp/sdiv_tb.sv
@@
   task automatic check_div(
       input signed [W-1:0] a,
       input signed [W-1:0] b,
       input signed [W-1:0] exp_q,
       input signed [W-1:0] exp_r
@@
     end
   endtask
+
+  task automatic check_model(
+      input signed [W-1:0] a,
+      input signed [W-1:0] b
+  );
+    integer aa;
+    integer bb;
+    integer q;
+    integer r;
+    reg signed [W-1:0] exp_q;
+    reg signed [W-1:0] exp_r;
+    begin
+      aa = a;
+      bb = b;
+
+      if (b == 16'sd0) begin
+        exp_q = a[W-1] ? 16'sh8000 : 16'sh7fff;
+        exp_r = a;
+      end else if ((a == 16'sh8000) && (b == -16'sd1)) begin
+        exp_q = 16'sh7fff;
+        exp_r = 16'sd0;
+      end else begin
+        q = aa / bb;
+        r = aa % bb;
+
+        if ((r != 0) && ((aa < 0) != (bb < 0))) begin
+          q = q - 1;
+          r = r + bb;
+        end
+
+        exp_q = q;
+        exp_r = r;
+      end
+
+      check_div(a, b, exp_q, exp_r);
+    end
+  endtask
@@
-    check_div( 16'sd7,      16'sd3,  16'sd2,     16'sd1);
-    check_div(-16'sd7,      16'sd3, -16'sd3,     16'sd2);
-    check_div( 16'sd7,     -16'sd3, -16'sd3,    -16'sd2);
-    check_div(-16'sd7,     -16'sd3,  16'sd2,    -16'sd1);
-    check_div( 16'sd9,      16'sd0, 16'sh7fff,   16'sd9);
-    check_div(-16'sd9,      16'sd0, 16'sh8000,  -16'sd9);
-    check_div( 16'sh8000,  -16'sd1, 16'sh7fff,   16'sd0);
+    check_model( 16'sd7,      16'sd3);
+    check_model(-16'sd7,      16'sd3);
+    check_model( 16'sd7,     -16'sd3);
+    check_model(-16'sd7,     -16'sd3);
+    check_model( 16'sd9,      16'sd0);
+    check_model(-16'sd9,      16'sd0);
+    check_model( 16'sh8000,  -16'sd1);
+    check_model( 16'sh8000,   16'sd2);
+    check_model( 16'sh8000,  -16'sd3);
+    check_model( 16'sh7fff,  -16'sd7);
+
+    repeat (100) begin
+      check_model($urandom, $urandom);
+    end
 
     $display("PASS");
*** End Patch


Exit code: 0
Wall time: 0 seconds
Output:
Success. Updated the following files:
M /tmp/sdiv_tb.sv
The randomized model checks are in the temporary testbench. I’m running the expanded simulation now.
shell
iverilog -g2012 -I sdiv_core/rtl -o /tmp/sdiv_tb.vvp /tmp/sdiv_tb.sv sdiv_core/rtl/sdiv.sv && vvp /tmp/sdiv_tb.vvp
output
Chunk ID: 90477c
Wall time: 0.0000 seconds
Process exited with code 0
Original token count: 2
Output:
PASS
The expanded simulation passes. I’m doing a final diff review to catch anything accidental before wrapping up.
shell
git diff -- sdiv_core/rtl/sdiv.sv
output
Chunk ID: ddf94d
Wall time: 0.0000 seconds
Process exited with code 127
Original token count: 11
Output:
/bin/bash: line 1: git: command not found
shell
git status --short
output
Chunk ID: 0bd47d
Wall time: 0.0000 seconds
Process exited with code 127
Original token count: 11
Output:
/bin/bash: line 1: git: command not found
shell
iverilog -g2012 -I sdiv_core/rtl -o /tmp/sdiv_compile.vvp sdiv_core/rtl/sdiv_top.sv sdiv_core/rtl/sdiv.sv
output
Chunk ID: 74b441
Wall time: 0.0000 seconds
Process exited with code 0
Original token count: 0
Output:
The final compile is clean. This environment doesn’t have `git`, so I can’t show a repository diff, but I’m checking the final file contents directly.
shell
sed -n '40,150p' sdiv_core/rtl/sdiv.sv
output
Chunk ID: 19e1d9
Wall time: 0.0000 seconds
Process exited with code 0
Original token count: 638
Output:

  // ---------------------------------------------------------------------------
  // 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

  logic        [2*W-1:0] result_w;
  logic signed [W-1:0]   result_q;
  logic signed [W-1:0]   result_r;

  function automatic [2*W-1:0] floor_div_result;
    input signed [W-1:0] a;
    input signed [W-1:0] b;

    reg signed [W-1:0] q_tmp;
    reg signed [W-1:0] r_tmp;
    reg signed [W-1:0] min_int;
    reg signed [W-1:0] max_int;
    reg signed [W-1:0] neg_one;
    begin
      min_int = {1'b1, {(W-1){1'b0}}};
      max_int = {1'b0, {(W-1){1'b1}}};
      neg_one = {W{1'b1}};

      if (b == '0) begin
        if (a[W-1]) begin
          q_tmp = min_int;
        end else begin
          q_tmp = max_int;
        end
        r_tmp = a;
      end else if ((a == min_int) && (b == neg_one)) begin
        q_tmp = max_int;
        r_tmp = '0;
      end else begin
        q_tmp = a / b;
        r_tmp = a % b;

        if ((r_tmp != '0) && (a[W-1] ^ b[W-1])) begin
          q_tmp = q_tmp - {{(W-1){1'b0}}, 1'b1};
          r_tmp = r_tmp + b;
        end
      end

      floor_div_result = {q_tmp, r_tmp};
    end
  endfunction

  assign result_w = floor_div_result(a_q, b_q);
  assign result_q = result_w[2*W-1:W];
  assign result_r = result_w[W-1:0];

  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) begin
          run       <= 1'b0;
          cnt       <= 8'd0;
          busy      <= 1'b0;
          valid     <= 1'b1;
          quotient  <= result_q;
          remainder <= result_r;
        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
        busy <= 1'b0;
      end
    end
  end

endmodule : sdiv
Implemented [sdiv.sv](/work/sdiv_core/rtl/sdiv.sv:50). What changed: - Added operand capture on accepted `start`. - Added fixed `N` cycle run counter with registered `busy`/`valid`. - Ensured `busy` and `valid` never overlap. - Added floored signed division correction. - Covered divide-by-zero and `-32768 / -1` overflow cases. - Kept outputs registered and reset asynchronously to zero. Verification run: - `iverilog -g2012 -I sdiv_core/rtl -o /tmp/sdiv_compile.vvp sdiv_core/rtl/sdiv_top.sv sdiv_core/rtl/sdiv.sv` - Local simulation with directed and 100 randomized cases: `PASS` `git` is not installed in this environment, so I couldn’t produce a git diff/status.
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_f935df2d17704991. Re-running the agent live requires EVAL_PLATFORM_ENABLE_OAUTH_SMOKE=1 and is non-deterministic.

Trial trial_f935df2d17704991 · verifier authoritative; classifier explanatory.