SyncValsverifier → artifact → classifier → verdict
SyncVals · Trajectory

open-drain-command-engine

codex gpt-5.5 ✗ failed HARNESS_ERROR ↑ 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
HARNESS_ERRORInfrastructure failure, the agent never ran properly. Not a signal about agent or task.
SubtypeMissing Task Artifacts
EvidenceTask directory `<repo>/.bench/artifacts/tasks/task_4a0d096810114548/v1-files/` contains only `instruction.md` and `task.toml`. Missing critical task components: `solution/solve.sh`, `solution/fix.patch`, `tests/test.sh`, and `environment/Dockerfile`. The test output shows 'MISMATCH_COUNTS cmd_ack=108 busy=0 al=582 bit_out=0 scl=54 sda=54' but without test source files, the nature and validity of these checks cannot be evaluated.
Root causeThe task artifact bundle is incomplete. Required directories (solution/, tests/, environment/) are missing from the v1-files, making it impossible to verify test correctness or compare against the reference solution.
RecommendationEnsure the task artifact directory contains all required paths per the Harbor contract: instruction.md, task.toml, environment/, solution/solve.sh, solution/fix.patch, and tests/test.sh. Verify that the task was properly uploaded and stored before running trials."
Trajectory
Tool-by-tool agent trajectory
23 tool calls · 2 tool types · 41 steps
<permissions instructions> Filesystem sandboxing defines which files can be read or written. `sandbox_mode` is `danger-full-access`: No filesystem sandboxing - all commands are permitted. Network access is enabled. Approval policy is currently never. Do not provide the `sandbox_permissions` for any reason, commands will be rejected. </permissions instructions><apps_instructions> ## Apps (Connectors) Apps (Connectors) can be explicitly triggered in user messages in the format `[$app-name](app://{connector_id})`. Apps can also be implicitly triggered as long as the context suggests usage of available apps. An app is equivalent to a set of MCP tools within the `codex_apps` MCP. An installed app's MCP tools are either provided to you already, or can be lazy-loaded through the `tool_search` tool. If `tool_search` is available, the apps that are searchable by `tools_search` will be listed by it. Do not additionally call list_mcp_resources or list_mcp_resource_templates for apps. </apps_instructions><skills_instructions> ## Skills A skill is a set of instructions provided through a `SKILL.md` source. Below is the list of skills that can be used. Each entry includes a name, description, and source locator. `file` locators are on the host filesystem, `environment resource` locators are owned by an execution environment, `orchestrator resource` locators are opaque non-filesystem resources, and `custom resource` locators use their provider's access mechanism. ### Available skills - imagegen: Generate or edit raster images when the task benefits from AI-created bitmap visuals such as photos, illustrations, textures, sprites, mockups, or transparent-background cutouts. Use when Codex should create a brand-new image, transform an existing image, or derive visual variants from references, and the output should be a bitmap asset rather than repo-native code or vector. Do not use when the task is better handled by editing existing SVG/vector/code-native assets, extending an established icon or logo system, or building the visual directly in HTML/CSS/canvas. (file: /tmp/codex-home/skills/.system/imagegen/SKILL.md) - openai-docs: Use when the user asks how to build with OpenAI products or APIs, asks about Codex itself or choosing Codex surfaces, needs up-to-date official documentation with citations, help choosing the latest model for a use case, or model upgrade and prompt-upgrade guidance; use OpenAI docs MCP tools for non-Codex docs questions, use the Codex manual helper first for broad Codex self-knowledge, and restrict fallback browsing to official OpenAI domains. (file: /tmp/codex-home/skills/.system/openai-docs/SKILL.md) - plugin-creator: Create and scaffold plugin directories for Codex with a required `.codex-plugin/plugin.json`, optional plugin folders/files, valid manifest defaults, and personal-marketplace entries by default. Use when Codex needs to create a new personal plugin, add optional plugin structure, generate or update marketplace entries for plugin ordering and availability metadata, or update an existing local plugin during development with the CLI-driven cachebuster and reinstall flow. (file: /tmp/codex-home/skills/.system/plugin-creator/SKILL.md) - skill-creator: Guide for creating effective skills. This skill should be used when users want to create a new skill (or update an existing skill) that extends Codex's capabilities with specialized knowledge, workflows, or tool integrations. (file: /tmp/codex-home/skills/.system/skill-creator/SKILL.md) - skill-installer: Install Codex skills into $CODEX_HOME/skills from a curated list or a [code-host] repo path. Use when a user asks to list installable skills, install a curated skill, or install a skill from another repo (including private repos). (file: /tmp/codex-home/skills/.system/skill-installer/SKILL.md) ### How to use skills - Discovery: The list above is the skills available in this session (name + description + source locator). `file` entries live on the host filesystem, `environment resource` entries are owned by their execution environment, `orchestrator resource` entries must be accessed through `skills.list` and `skills.read`, and `custom resource` entries use their provider's access mechanism. - Trigger rules: If the user names a skill (with `$SkillName` or plain text) OR the task clearly matches a skill's description shown above, you must use that skill for that turn. Multiple mentions mean use them all. Do not carry skills across turns unless re-mentioned. - Missing/blocked: If a named skill isn't in the list or its source can't be read, say so briefly and continue with the best fallback. - How to use a skill (progressive disclosure): 1) After deciding to use a skill, the main agent must read its `SKILL.md` completely before taking task actions. For a `file` entry, open the listed path. For an `environment resource`, use the filesystem of the owning environment. For an `orchestrator resource`, call `skills.list` with `{"authority":{"kind":"orchestrator"}}`, select the matching package, and pass its `main_resource` to `skills.read`. If a read is truncated or paginated, continue until EOF. 2) When `SKILL.md` references another resource, use the same access mechanism. Resolve relative paths against a filesystem-backed skill directory. For orchestrator skills, pass the exact referenced resource identifier with the same authority and package to `skills.read`; do not treat `skill://` identifiers as filesystem paths. 3) If `SKILL.md` points to extra folders such as `references/`, use its routing instructions to identify the resources required for the task. The main agent must read each required instruction or reference file itself before acting on it. Do not delegate reading, summarizing, or interpreting skill instructions to a subagent. Subagents may still perform task work when the selected skill allows it. 4) For filesystem-backed skills, prefer running or patching provided scripts instead of retyping large code blocks. For orchestrator skills, use `skills.read` and the available tools; do not invent a local path. 5) Reuse provided assets or templates through the same source access mechanism instead of recreating them. - Coordination and sequencing: - If multiple skills apply, choose the minimal set that covers the request and state the order you'll use them. - Announce which skill(s) you're using and why (one short line). If you skip an obvious skill, say why. - Context hygiene: - Progressive disclosure applies to selecting relevant files, not partially reading a selected instruction file. Do not load unrelated references, scripts, or assets. - Avoid deep reference-chasing: prefer opening only files directly linked from `SKILL.md` unless you're blocked. - When variants exist (frameworks, providers, domains), pick only the relevant reference file(s) and note that choice. - Safety and fallback: If a skill can't be applied cleanly (missing files, unclear instructions), state the issue, pick the next-best approach, and continue. </skills_instructions>
<environment_context> <cwd>/app</cwd> <shell>bash</shell> <current_date>2026-06-20</current_date> <timezone>Etc/UTC</timezone> <filesystem><workspace_roots><root>/app</root></workspace_roots><permission_profile type="disabled"><file_system type="unrestricted" /></permission_profile></filesystem> </environment_context>
Implement `/app/dut.sv`. Define `TopModule` with this port list: `input clk, rst, cmd_valid, bit_in, scl_i, sda_i; input [1:0] cmd; output cmd_ack, busy, al, bit_out, scl_drive_low, sda_drive_low;`. Define another module and instantiate it from `TopModule`. `rst` is synchronous active high and clears outputs to 0. All outputs are registered. `cmd_ack` is a one-cycle completion pulse. Accept a command only when none is active; `cmd=0` may be accepted while idle or busy, and other commands only while `busy` is high. Illegal commands leave outputs unchanged and do not acknowledge. The line controls are open-drain: 1 pulls low, 0 releases. The command-accept edge only loads the first registered phase; it must not also consume `scl_i` or sample `sda_i` for phase completion. Because every output is registered, when a later phase says "until `scl_i` is high", the clock edge that observes high only records that fact; the next visible line-drive/ack phase appears on the following clock. Command acceptance itself is a visible registered phase: for stop, write, and read, the line-drive values loaded on the accept edge must be held through one additional full clocked setup cycle before the SCL-release phase begins. `cmd=0` starts or restarts ownership: release both lines on accept, then in following clocked wait phase keep both released until `scl_i` is high, keep SCL released while pulling SDA low for one full cycle, then pull SCL low and pulse `cmd_ack`; `busy` is set from the accept edge. `cmd=1` stops: drive both low on accept, keep both low for the following setup cycle, release SCL until `scl_i` is high, then release SDA, clear `busy`, and pulse `cmd_ack` on the following clock. `cmd=2` writes `bit_in`: on accept drive SCL low and drive SDA low for 0 or released for 1, keep those drive values for the following setup cycle, release SCL until `scl_i` is high, then pull SCL low and acknowledge on the following clock. `cmd=3` reads: on accept drive SCL low and release SDA, keep those drive values for the following setup cycle, release SCL until `scl_i` is high, sample `sda_i` on that high-SCL edge into `bit_out`, then pull SCL low and acknowledge on the following clock. `al` is sticky until reset and asserts only during start or write-1 high-SCL phases when released SDA is observed low.
I’ll inspect the workspace and any existing `dut.sv` context first, then implement the state machine directly in the repo style.
shell
pwd && rg --files -g 'dut.sv' -g '*.sv' -g '*.v'
output
Chunk ID: 43fd4f
Wall time: 0.0000 seconds
Process exited with code 1
Original token count: 2
Output:
/app
shell
ls -la /app
output
Chunk ID: e18912
Wall time: 0.0000 seconds
Process exited with code 0
Original token count: 24
Output:
total 8
drwxr-xr-x 2 root root 4096 Jun 19 22:02 .
drwxr-xr-x 1 root root 4096 Jun 20 17:12 ..
`/app` is essentially empty, so this is a fresh implementation. I’m going to create `dut.sv` with a thin `TopModule` wrapper and a separate controller module that owns the registered state and outputs.
I’ve mapped the timing into explicit visible phases: accept, setup/wait, high-seen delay, then completion. That avoids consuming `scl_i` on the accept edge and preserves the extra registered cycle before any SCL-release phase.
apply_patch
*** Begin Patch
*** Add File: /app/dut.sv
+module TopModule (
+    input  logic       clk,
+    input  logic       rst,
+    input  logic       cmd_valid,
+    input  logic       bit_in,
+    input  logic       scl_i,
+    input  logic       sda_i,
+    input  logic [1:0] cmd,
+    output logic       cmd_ack,
+    output logic       busy,
+    output logic       al,
+    output logic       bit_out,
+    output logic       scl_drive_low,
+    output logic       sda_drive_low
+);
+
+    I2cBitController controller (
+        .clk(clk),
+        .rst(rst),
+        .cmd_valid(cmd_valid),
+        .bit_in(bit_in),
+        .scl_i(scl_i),
+        .sda_i(sda_i),
+        .cmd(cmd),
+        .cmd_ack(cmd_ack),
+        .busy(busy),
+        .al(al),
+        .bit_out(bit_out),
+        .scl_drive_low(scl_drive_low),
+        .sda_drive_low(sda_drive_low)
+    );
+
+endmodule
+
+module I2cBitController (
+    input  logic       clk,
+    input  logic       rst,
+    input  logic       cmd_valid,
+    input  logic       bit_in,
+    input  logic       scl_i,
+    input  logic       sda_i,
+    input  logic [1:0] cmd,
+    output logic       cmd_ack,
+    output logic       busy,
+    output logic       al,
+    output logic       bit_out,
+    output logic       scl_drive_low,
+    output logic       sda_drive_low
+);
+
+    localparam logic [1:0] CMD_START = 2'd0;
+    localparam logic [1:0] CMD_STOP  = 2'd1;
+    localparam logic [1:0] CMD_WRITE = 2'd2;
+    localparam logic [1:0] CMD_READ  = 2'd3;
+
+    typedef enum logic [4:0] {
+        ST_READY,
+        ST_START_ACCEPT,
+        ST_START_WAIT,
+        ST_START_SEEN,
+        ST_START_SDA_LOW,
+        ST_START_ACK,
+        ST_STOP_ACCEPT,
+        ST_STOP_SETUP,
+        ST_STOP_WAIT,
+        ST_STOP_SEEN,
+        ST_STOP_ACK,
+        ST_WRITE_ACCEPT,
+        ST_WRITE_SETUP,
+        ST_WRITE_WAIT,
+        ST_WRITE_SEEN,
+        ST_WRITE_ACK,
+        ST_READ_ACCEPT,
+        ST_READ_SETUP,
+        ST_READ_WAIT,
+        ST_READ_SEEN,
+        ST_READ_ACK
+    } state_t;
+
+    state_t state;
+    logic write_bit;
+
+    function automatic logic command_is_legal(input logic [1:0] command,
+                                              input logic is_busy);
+        command_is_legal = (command == CMD_START) || is_busy;
+    endfunction
+
+    task automatic hold_lines;
+        begin
+            scl_drive_low <= scl_drive_low;
+            sda_drive_low <= sda_drive_low;
+        end
+    endtask
+
+    task automatic accept_command;
+        begin
+            case (cmd)
+                CMD_START: begin
+                    state         <= ST_START_ACCEPT;
+                    busy          <= 1'b1;
+                    scl_drive_low <= 1'b0;
+                    sda_drive_low <= 1'b0;
+                end
+
+                CMD_STOP: begin
+                    state         <= ST_STOP_ACCEPT;
+                    scl_drive_low <= 1'b1;
+                    sda_drive_low <= 1'b1;
+                end
+
+                CMD_WRITE: begin
+                    state         <= ST_WRITE_ACCEPT;
+                    write_bit     <= bit_in;
+                    scl_drive_low <= 1'b1;
+                    sda_drive_low <= ~bit_in;
+                end
+
+                CMD_READ: begin
+                    state         <= ST_READ_ACCEPT;
+                    scl_drive_low <= 1'b1;
+                    sda_drive_low <= 1'b0;
+                end
+
+                default: begin
+                    state <= ST_READY;
+                end
+            endcase
+
+            cmd_ack <= 1'b0;
+        end
+    endtask
+
+    always_ff @(posedge clk) begin
+        if (rst) begin
+            state         <= ST_READY;
+            write_bit     <= 1'b0;
+            cmd_ack       <= 1'b0;
+            busy          <= 1'b0;
+            al            <= 1'b0;
+            bit_out       <= 1'b0;
+            scl_drive_low <= 1'b0;
+            sda_drive_low <= 1'b0;
+        end else begin
+            cmd_ack <= 1'b0;
+
+            case (state)
+                ST_READY: begin
+                    if (cmd_valid && command_is_legal(cmd, busy)) begin
+                        accept_command();
+                    end
+                end
+
+                ST_START_ACCEPT: begin
+                    state         <= ST_START_WAIT;
+                    scl_drive_low <= 1'b0;
+                    sda_drive_low <= 1'b0;
+                end
+
+                ST_START_WAIT: begin
+                    scl_drive_low <= 1'b0;
+                    sda_drive_low <= 1'b0;
+                    if (scl_i) begin
+                        state <= ST_START_SEEN;
+                        if (!sda_i) begin
+                            al <= 1'b1;
+                        end
+                    end
+                end
+
+                ST_START_SEEN: begin
+                    state         <= ST_START_SDA_LOW;
+                    scl_drive_low <= 1'b0;
+                    sda_drive_low <= 1'b0;
+                    if (scl_i && !sda_i) begin
+                        al <= 1'b1;
+                    end
+                end
+
+                ST_START_SDA_LOW: begin
+                    state         <= ST_START_ACK;
+                    scl_drive_low <= 1'b0;
+                    sda_drive_low <= 1'b1;
+                end
+
+                ST_START_ACK: begin
+                    scl_drive_low <= 1'b1;
+                    sda_drive_low <= 1'b1;
+                    cmd_ack       <= 1'b1;
+                    if (cmd_valid && command_is_legal(cmd, busy)) begin
+                        accept_command();
+                    end else begin
+                        state <= ST_READY;
+                    end
+                end
+
+                ST_STOP_ACCEPT: begin
+                    state         <= ST_STOP_SETUP;
+                    scl_drive_low <= 1'b1;
+                    sda_drive_low <= 1'b1;
+                end
+
+                ST_STOP_SETUP: begin
+                    state         <= ST_STOP_WAIT;
+                    scl_drive_low <= 1'b1;
+                    sda_drive_low <= 1'b1;
+                end
+
+                ST_STOP_WAIT: begin
+                    scl_drive_low <= 1'b0;
+                    sda_drive_low <= 1'b1;
+                    if (scl_i) begin
+                        state <= ST_STOP_SEEN;
+                    end
+                end
+
+                ST_STOP_SEEN: begin
+                    state         <= ST_STOP_ACK;
+                    scl_drive_low <= 1'b0;
+                    sda_drive_low <= 1'b1;
+                end
+
+                ST_STOP_ACK: begin
+                    busy          <= 1'b0;
+                    scl_drive_low <= 1'b0;
+                    sda_drive_low <= 1'b0;
+                    cmd_ack       <= 1'b1;
+                    if (cmd_valid && command_is_legal(cmd, 1'b0)) begin
+                        accept_command();
+                    end else begin
+                        state <= ST_READY;
+                    end
+                end
+
+                ST_WRITE_ACCEPT: begin
+                    state         <= ST_WRITE_SETUP;
+                    scl_drive_low <= 1'b1;
+                    sda_drive_low <= ~write_bit;
+                end
+
+                ST_WRITE_SETUP: begin
+                    state         <= ST_WRITE_WAIT;
+                    scl_drive_low <= 1'b1;
+                    sda_drive_low <= ~write_bit;
+                end
+
+                ST_WRITE_WAIT: begin
+                    scl_drive_low <= 1'b0;
+                    sda_drive_low <= ~write_bit;
+                    if (scl_i) begin
+                        state <= ST_WRITE_SEEN;
+                        if (write_bit && !sda_i) begin
+                            al <= 1'b1;
+                        end
+                    end
+                end
+
+                ST_WRITE_SEEN: begin
+                    state         <= ST_WRITE_ACK;
+                    scl_drive_low <= 1'b0;
+                    sda_drive_low <= ~write_bit;
+                    if (scl_i && write_bit && !sda_i) begin
+                        al <= 1'b1;
+                    end
+                end
+
+                ST_WRITE_ACK: begin
+                    scl_drive_low <= 1'b1;
+                    sda_drive_low <= ~write_bit;
+                    cmd_ack       <= 1'b1;
+                    if (cmd_valid && command_is_legal(cmd, busy)) begin
+                        accept_command();
+                    end else begin
+                        state <= ST_READY;
+                    end
+                end
+
+                ST_READ_ACCEPT: begin
+                    state         <= ST_READ_SETUP;
+                    scl_drive_low <= 1'b1;
+                    sda_drive_low <= 1'b0;
+                end
+
+                ST_READ_SETUP: begin
+                    state         <= ST_READ_WAIT;
+                    scl_drive_low <= 1'b1;
+                    sda_drive_low <= 1'b0;
+                end
+
+                ST_READ_WAIT: begin
+                    scl_drive_low <= 1'b0;
+                    sda_drive_low <= 1'b0;
+                    if (scl_i) begin
+                        state   <= ST_READ_SEEN;
+                        bit_out <= sda_i;
+                    end
+                end
+
+                ST_READ_SEEN: begin
+                    state         <= ST_READ_ACK;
+                    scl_drive_low <= 1'b0;
+                    sda_drive_low <= 1'b0;
+                end
+
+                ST_READ_ACK: begin
+                    scl_drive_low <= 1'b1;
+                    sda_drive_low <= 1'b0;
+                    cmd_ack       <= 1'b1;
+                    if (cmd_valid && command_is_legal(cmd, busy)) begin
+                        accept_command();
+                    end else begin
+                        state <= ST_READY;
+                    end
+                end
+
+                default: begin
+                    state <= ST_READY;
+                    hold_lines();
+                end
+            endcase
+        end
+    end
+
+endmodule
*** End Patch


Exit code: 0
Wall time: 0 seconds
Output:
Success. Updated the following files:
A /app/dut.sv
One timing issue showed up in the first pass: the completion pulse needs to be loaded when entering the ack phase, not one state later. I’m tightening those transitions so the visible ack phase is exactly one cycle and can be followed immediately by a new legal accept.
apply_patch
*** Begin Patch
*** Update File: /app/dut.sv
@@
                 ST_START_SDA_LOW: begin
                     state         <= ST_START_ACK;
-                    scl_drive_low <= 1'b0;
+                    scl_drive_low <= 1'b1;
                     sda_drive_low <= 1'b1;
+                    cmd_ack       <= 1'b1;
                 end
 
                 ST_START_ACK: begin
-                    scl_drive_low <= 1'b1;
-                    sda_drive_low <= 1'b1;
-                    cmd_ack       <= 1'b1;
                     if (cmd_valid && command_is_legal(cmd, busy)) begin
                         accept_command();
                     end else begin
                         state <= ST_READY;
@@
                 ST_STOP_SEEN: begin
                     state         <= ST_STOP_ACK;
-                    scl_drive_low <= 1'b0;
-                    sda_drive_low <= 1'b1;
+                    busy          <= 1'b0;
+                    scl_drive_low <= 1'b0;
+                    sda_drive_low <= 1'b0;
+                    cmd_ack       <= 1'b1;
                 end
 
                 ST_STOP_ACK: begin
-                    busy          <= 1'b0;
-                    scl_drive_low <= 1'b0;
-                    sda_drive_low <= 1'b0;
-                    cmd_ack       <= 1'b1;
                     if (cmd_valid && command_is_legal(cmd, 1'b0)) begin
                         accept_command();
                     end else begin
                         state <= ST_READY;
@@
                 ST_WRITE_SEEN: begin
                     state         <= ST_WRITE_ACK;
-                    scl_drive_low <= 1'b0;
+                    scl_drive_low <= 1'b1;
                     sda_drive_low <= ~write_bit;
+                    cmd_ack       <= 1'b1;
                     if (scl_i && write_bit && !sda_i) begin
                         al <= 1'b1;
                     end
                 end
 
                 ST_WRITE_ACK: begin
-                    scl_drive_low <= 1'b1;
-                    sda_drive_low <= ~write_bit;
-                    cmd_ack       <= 1'b1;
                     if (cmd_valid && command_is_legal(cmd, busy)) begin
                         accept_command();
                     end else begin
                         state <= ST_READY;
@@
                 ST_READ_SEEN: begin
                     state         <= ST_READ_ACK;
-                    scl_drive_low <= 1'b0;
+                    scl_drive_low <= 1'b1;
                     sda_drive_low <= 1'b0;
+                    cmd_ack       <= 1'b1;
                 end
 
                 ST_READ_ACK: begin
-                    scl_drive_low <= 1'b1;
-                    sda_drive_low <= 1'b0;
-                    cmd_ack       <= 1'b1;
                     if (cmd_valid && command_is_legal(cmd, busy)) begin
                         accept_command();
                     end else begin
*** End Patch


Exit code: 0
Wall time: 0 seconds
Output:
Success. Updated the following files:
M /app/dut.sv
The file now has the explicit ack-entry transitions. I’m going to run a syntax check next, then I’ll do a small simulation sanity check for the command phase timing.
shell
sed -n '1,260p' /app/dut.sv
output
Chunk ID: 15029a
Wall time: 0.0000 seconds
Process exited with code 0
Original token count: 1947
Output:
module TopModule (
    input  logic       clk,
    input  logic       rst,
    input  logic       cmd_valid,
    input  logic       bit_in,
    input  logic       scl_i,
    input  logic       sda_i,
    input  logic [1:0] cmd,
    output logic       cmd_ack,
    output logic       busy,
    output logic       al,
    output logic       bit_out,
    output logic       scl_drive_low,
    output logic       sda_drive_low
);

    I2cBitController controller (
        .clk(clk),
        .rst(rst),
        .cmd_valid(cmd_valid),
        .bit_in(bit_in),
        .scl_i(scl_i),
        .sda_i(sda_i),
        .cmd(cmd),
        .cmd_ack(cmd_ack),
        .busy(busy),
        .al(al),
        .bit_out(bit_out),
        .scl_drive_low(scl_drive_low),
        .sda_drive_low(sda_drive_low)
    );

endmodule

module I2cBitController (
    input  logic       clk,
    input  logic       rst,
    input  logic       cmd_valid,
    input  logic       bit_in,
    input  logic       scl_i,
    input  logic       sda_i,
    input  logic [1:0] cmd,
    output logic       cmd_ack,
    output logic       busy,
    output logic       al,
    output logic       bit_out,
    output logic       scl_drive_low,
    output logic       sda_drive_low
);

    localparam logic [1:0] CMD_START = 2'd0;
    localparam logic [1:0] CMD_STOP  = 2'd1;
    localparam logic [1:0] CMD_WRITE = 2'd2;
    localparam logic [1:0] CMD_READ  = 2'd3;

    typedef enum logic [4:0] {
        ST_READY,
        ST_START_ACCEPT,
        ST_START_WAIT,
        ST_START_SEEN,
        ST_START_SDA_LOW,
        ST_START_ACK,
        ST_STOP_ACCEPT,
        ST_STOP_SETUP,
        ST_STOP_WAIT,
        ST_STOP_SEEN,
        ST_STOP_ACK,
        ST_WRITE_ACCEPT,
        ST_WRITE_SETUP,
        ST_WRITE_WAIT,
        ST_WRITE_SEEN,
        ST_WRITE_ACK,
        ST_READ_ACCEPT,
        ST_READ_SETUP,
        ST_READ_WAIT,
        ST_READ_SEEN,
        ST_READ_ACK
    } state_t;

    state_t state;
    logic write_bit;

    function automatic logic command_is_legal(input logic [1:0] command,
                                              input logic is_busy);
        command_is_legal = (command == CMD_START) || is_busy;
    endfunction

    task automatic hold_lines;
        begin
            scl_drive_low <= scl_drive_low;
            sda_drive_low <= sda_drive_low;
        end
    endtask

    task automatic accept_command;
        begin
            case (cmd)
                CMD_START: begin
                    state         <= ST_START_ACCEPT;
                    busy          <= 1'b1;
                    scl_drive_low <= 1'b0;
                    sda_drive_low <= 1'b0;
                end

                CMD_STOP: begin
                    state         <= ST_STOP_ACCEPT;
                    scl_drive_low <= 1'b1;
                    sda_drive_low <= 1'b1;
                end

                CMD_WRITE: begin
                    state         <= ST_WRITE_ACCEPT;
                    write_bit     <= bit_in;
                    scl_drive_low <= 1'b1;
                    sda_drive_low <= ~bit_in;
                end

                CMD_READ: begin
                    state         <= ST_READ_ACCEPT;
                    scl_drive_low <= 1'b1;
                    sda_drive_low <= 1'b0;
                end

                default: begin
                    state <= ST_READY;
                end
            endcase

            cmd_ack <= 1'b0;
        end
    endtask

    always_ff @(posedge clk) begin
        if (rst) begin
            state         <= ST_READY;
            write_bit     <= 1'b0;
            cmd_ack       <= 1'b0;
            busy          <= 1'b0;
            al            <= 1'b0;
            bit_out       <= 1'b0;
            scl_drive_low <= 1'b0;
            sda_drive_low <= 1'b0;
        end else begin
            cmd_ack <= 1'b0;

            case (state)
                ST_READY: begin
                    if (cmd_valid && command_is_legal(cmd, busy)) begin
                        accept_command();
                    end
                end

                ST_START_ACCEPT: begin
                    state         <= ST_START_WAIT;
                    scl_drive_low <= 1'b0;
                    sda_drive_low <= 1'b0;
                end

                ST_START_WAIT: begin
                    scl_drive_low <= 1'b0;
                    sda_drive_low <= 1'b0;
                    if (scl_i) begin
                        state <= ST_START_SEEN;
                        if (!sda_i) begin
                            al <= 1'b1;
                        end
                    end
                end

                ST_START_SEEN: begin
                    state         <= ST_START_SDA_LOW;
                    scl_drive_low <= 1'b0;
                    sda_drive_low <= 1'b0;
                    if (scl_i && !sda_i) begin
                        al <= 1'b1;
                    end
                end

                ST_START_SDA_LOW: begin
                    state         <= ST_START_ACK;
                    scl_drive_low <= 1'b1;
                    sda_drive_low <= 1'b1;
                    cmd_ack       <= 1'b1;
                end

                ST_START_ACK: begin
                    if (cmd_valid && command_is_legal(cmd, busy)) begin
                        accept_command();
                    end else begin
                        state <= ST_READY;
                    end
                end

                ST_STOP_ACCEPT: begin
                    state         <= ST_STOP_SETUP;
                    scl_drive_low <= 1'b1;
                    sda_drive_low <= 1'b1;
                end

                ST_STOP_SETUP: begin
                    state         <= ST_STOP_WAIT;
                    scl_drive_low <= 1'b1;
                    sda_drive_low <= 1'b1;
                end

                ST_STOP_WAIT: begin
                    scl_drive_low <= 1'b0;
                    sda_drive_low <= 1'b1;
                    if (scl_i) begin
                        state <= ST_STOP_SEEN;
                    end
                end

                ST_STOP_SEEN: begin
                    state         <= ST_STOP_ACK;
                    busy          <= 1'b0;
                    scl_drive_low <= 1'b0;
                    sda_drive_low <= 1'b0;
                    cmd_ack       <= 1'b1;
                end

                ST_STOP_ACK: begin
                    if (cmd_valid && command_is_legal(cmd, 1'b0)) begin
                        accept_command();
                    end else begin
                        state <= ST_READY;
                    end
                end

                ST_WRITE_ACCEPT: begin
                    state         <= ST_WRITE_SETUP;
                    scl_drive_low <= 1'b1;
                    sda_drive_low <= ~write_bit;
                end

                ST_WRITE_SETUP: begin
                    state         <= ST_WRITE_WAIT;
                    scl_drive_low <= 1'b1;
                    sda_drive_low <= ~write_bit;
                end

                ST_WRITE_WAIT: begin
                    scl_drive_low <= 1'b0;
                    sda_drive_low <= ~write_bit;
                    if (scl_i) begin
                        state <= ST_WRITE_SEEN;
                        if (write_bit && !sda_i) begin
                            al <= 1'b1;
                        end
                    end
                end

                ST_WRITE_SEEN: begin
                    state         <= ST_WRITE_ACK;
                    scl_drive_low <= 1'b1;
                    sda_drive_low <= ~write_bit;
                    cmd_ack       <= 1'b1;
                    if (scl_i && write_bit && !sda_i) begin
                        al <= 1'b1;
                    end
shell
command -v iverilog || command -v verilator || true
output
Chunk ID: 755539
Wall time: 0.0000 seconds
Process exited with code 0
Original token count: 5
Output:
/usr/bin/iverilog
shell
sed -n '261,520p' /app/dut.sv && iverilog -g2012 -Wall -tnull /app/dut.sv
output
Chunk ID: f8cbcd
Wall time: 0.0000 seconds
Process exited with code 0
Original token count: 416
Output:
                end

                ST_WRITE_ACK: begin
                    if (cmd_valid && command_is_legal(cmd, busy)) begin
                        accept_command();
                    end else begin
                        state <= ST_READY;
                    end
                end

                ST_READ_ACCEPT: begin
                    state         <= ST_READ_SETUP;
                    scl_drive_low <= 1'b1;
                    sda_drive_low <= 1'b0;
                end

                ST_READ_SETUP: begin
                    state         <= ST_READ_WAIT;
                    scl_drive_low <= 1'b1;
                    sda_drive_low <= 1'b0;
                end

                ST_READ_WAIT: begin
                    scl_drive_low <= 1'b0;
                    sda_drive_low <= 1'b0;
                    if (scl_i) begin
                        state   <= ST_READ_SEEN;
                        bit_out <= sda_i;
                    end
                end

                ST_READ_SEEN: begin
                    state         <= ST_READ_ACK;
                    scl_drive_low <= 1'b1;
                    sda_drive_low <= 1'b0;
                    cmd_ack       <= 1'b1;
                end

                ST_READ_ACK: begin
                    if (cmd_valid && command_is_legal(cmd, busy)) begin
                        accept_command();
                    end else begin
                        state <= ST_READY;
                    end
                end

                default: begin
                    state <= ST_READY;
                    hold_lines();
                end
            endcase
        end
    end

endmodule
The syntax check passed, but reviewing the phase-to-output mapping exposed a subtle off-by-one in a few transitions: a state transition must load the outputs for the phase being entered. I’m fixing those SCL-release and SDA-low entries now.
apply_patch
*** Begin Patch
*** Update File: /app/dut.sv
@@
                 ST_START_SEEN: begin
                     state         <= ST_START_SDA_LOW;
                     scl_drive_low <= 1'b0;
-                    sda_drive_low <= 1'b0;
+                    sda_drive_low <= 1'b1;
                     if (scl_i && !sda_i) begin
                         al <= 1'b1;
                     end
                 end
@@
                 ST_STOP_SETUP: begin
                     state         <= ST_STOP_WAIT;
-                    scl_drive_low <= 1'b1;
+                    scl_drive_low <= 1'b0;
                     sda_drive_low <= 1'b1;
                 end
@@
                 ST_WRITE_SETUP: begin
                     state         <= ST_WRITE_WAIT;
-                    scl_drive_low <= 1'b1;
+                    scl_drive_low <= 1'b0;
                     sda_drive_low <= ~write_bit;
                 end
@@
                 ST_READ_SETUP: begin
                     state         <= ST_READ_WAIT;
-                    scl_drive_low <= 1'b1;
+                    scl_drive_low <= 1'b0;
                     sda_drive_low <= 1'b0;
                 end
*** End Patch


Exit code: 0
Wall time: 0 seconds
Output:
Success. Updated the following files:
M /app/dut.sv
shell
iverilog -g2012 -Wall -tnull /app/dut.sv
output
Chunk ID: 488cfe
Wall time: 0.0000 seconds
Process exited with code 0
Original token count: 0
Output:
shell
command -v verilator || true
output
Chunk ID: 3f4fd1
Wall time: 0.0000 seconds
Process exited with code 0
Original token count: 0
Output:
Syntax is clean. I’m adding a temporary self-checking testbench just long enough to verify reset, illegal idle commands, start timing, immediate post-ack accept, stop timing, read sampling, and sticky arbitration lost behavior.
apply_patch
*** Begin Patch
*** Add File: /app/tb_tmp.sv
+module tb;
+    logic clk;
+    logic rst;
+    logic cmd_valid;
+    logic bit_in;
+    logic scl_i;
+    logic sda_i;
+    logic [1:0] cmd;
+    logic cmd_ack;
+    logic busy;
+    logic al;
+    logic bit_out;
+    logic scl_drive_low;
+    logic sda_drive_low;
+
+    TopModule dut (
+        .clk(clk),
+        .rst(rst),
+        .cmd_valid(cmd_valid),
+        .bit_in(bit_in),
+        .scl_i(scl_i),
+        .sda_i(sda_i),
+        .cmd(cmd),
+        .cmd_ack(cmd_ack),
+        .busy(busy),
+        .al(al),
+        .bit_out(bit_out),
+        .scl_drive_low(scl_drive_low),
+        .sda_drive_low(sda_drive_low)
+    );
+
+    initial clk = 1'b0;
+    always #5 clk = ~clk;
+
+    task automatic tick;
+        begin
+            @(posedge clk);
+            #1;
+        end
+    endtask
+
+    task automatic expect(input logic exp_ack,
+                          input logic exp_busy,
+                          input logic exp_al,
+                          input logic exp_bit_out,
+                          input logic exp_scl_low,
+                          input logic exp_sda_low,
+                          input string label);
+        begin
+            if ({cmd_ack, busy, al, bit_out, scl_drive_low, sda_drive_low} !==
+                {exp_ack, exp_busy, exp_al, exp_bit_out, exp_scl_low, exp_sda_low}) begin
+                $display("FAIL %s: got ack=%0b busy=%0b al=%0b bit=%0b scl=%0b sda=%0b",
+                         label, cmd_ack, busy, al, bit_out, scl_drive_low, sda_drive_low);
+                $finish;
+            end
+        end
+    endtask
+
+    initial begin
+        rst = 1'b1;
+        cmd_valid = 1'b0;
+        bit_in = 1'b0;
+        scl_i = 1'b1;
+        sda_i = 1'b1;
+        cmd = 2'd0;
+        tick();
+        expect(0, 0, 0, 0, 0, 0, "reset");
+
+        rst = 1'b0;
+        cmd_valid = 1'b1;
+        cmd = 2'd1;
+        tick();
+        expect(0, 0, 0, 0, 0, 0, "illegal stop idle");
+
+        cmd = 2'd0;
+        tick();
+        expect(0, 1, 0, 0, 0, 0, "start accept");
+
+        cmd_valid = 1'b0;
+        tick();
+        expect(0, 1, 0, 0, 0, 0, "start wait");
+
+        tick();
+        expect(0, 1, 0, 0, 0, 0, "start seen");
+
+        tick();
+        expect(0, 1, 0, 0, 0, 1, "start sda low");
+
+        tick();
+        expect(1, 1, 0, 0, 1, 1, "start ack");
+
+        cmd_valid = 1'b1;
+        cmd = 2'd1;
+        tick();
+        expect(0, 1, 0, 0, 1, 1, "stop accept after ack");
+
+        cmd_valid = 1'b0;
+        tick();
+        expect(0, 1, 0, 0, 1, 1, "stop setup");
+
+        tick();
+        expect(0, 1, 0, 0, 0, 1, "stop wait");
+
+        tick();
+        expect(0, 1, 0, 0, 0, 1, "stop seen");
+
+        tick();
+        expect(1, 0, 0, 0, 0, 0, "stop ack");
+
+        cmd_valid = 1'b1;
+        cmd = 2'd0;
+        tick();
+        cmd_valid = 1'b0;
+        repeat (4) tick();
+        expect(1, 1, 0, 0, 1, 1, "restart ack");
+
+        cmd_valid = 1'b1;
+        cmd = 2'd3;
+        sda_i = 1'b1;
+        tick();
+        expect(0, 1, 0, 0, 1, 0, "read accept");
+
+        cmd_valid = 1'b0;
+        tick();
+        expect(0, 1, 0, 0, 1, 0, "read setup");
+
+        tick();
+        expect(0, 1, 0, 0, 0, 0, "read wait");
+
+        tick();
+        expect(0, 1, 0, 1, 0, 0, "read seen sampled");
+
+        tick();
+        expect(1, 1, 0, 1, 1, 0, "read ack");
+
+        cmd_valid = 1'b1;
+        cmd = 2'd2;
+        bit_in = 1'b1;
+        sda_i = 1'b0;
+        tick();
+        cmd_valid = 1'b0;
+        tick();
+        tick();
+        expect(0, 1, 0, 1, 0, 0, "write wait one");
+
+        tick();
+        expect(0, 1, 1, 1, 0, 0, "write al seen");
+
+        tick();
+        expect(1, 1, 1, 1, 1, 0, "write ack al sticky");
+
+        $display("PASS");
+        $finish;
+    end
+endmodule
*** End Patch


Exit code: 0
Wall time: 0 seconds
Output:
Success. Updated the following files:
A /app/tb_tmp.sv
The temporary checks cover the visible cycle sequence rather than just compilation. I’m compiling the testbench now, then I’ll remove it so only the requested DUT remains.
shell
iverilog -g2012 -Wall -o /tmp/dut_tb.vvp /app/dut.sv /app/tb_tmp.sv
output
Chunk ID: 0e4fa3
Wall time: 0.0000 seconds
Process exited with code 88
Original token count: 948
Output:
/app/tb_tmp.sv:42: syntax error
/app/tb_tmp.sv:48: error: Invalid module item.
/app/tb_tmp.sv:49: syntax error
/app/tb_tmp.sv:53: error: Invalid module item.
/app/tb_tmp.sv:55: syntax error
/app/tb_tmp.sv:60: error: Invalid module item.
/app/tb_tmp.sv:61: syntax error
/app/tb_tmp.sv:61: error: Invalid module instantiation
/app/tb_tmp.sv:62: error: Invalid module instantiation
/app/tb_tmp.sv:63: error: Invalid module instantiation
/app/tb_tmp.sv:64: error: Invalid module instantiation
/app/tb_tmp.sv:65: error: Invalid module instantiation
/app/tb_tmp.sv:67: syntax error
/app/tb_tmp.sv:67: error: Invalid module item.
/app/tb_tmp.sv:69: syntax error
/app/tb_tmp.sv:69: error: Invalid module instantiation
/app/tb_tmp.sv:70: error: Invalid module instantiation
/app/tb_tmp.sv:71: error: Invalid module instantiation
/app/tb_tmp.sv:73: syntax error
/app/tb_tmp.sv:73: error: Invalid module item.
/app/tb_tmp.sv:75: syntax error
/app/tb_tmp.sv:75: error: Invalid module instantiation
/app/tb_tmp.sv:77: syntax error
/app/tb_tmp.sv:77: error: Invalid module item.
/app/tb_tmp.sv:79: syntax error
/app/tb_tmp.sv:79: error: Invalid module instantiation
/app/tb_tmp.sv:81: syntax error
/app/tb_tmp.sv:81: error: Invalid module item.
/app/tb_tmp.sv:84: syntax error
/app/tb_tmp.sv:84: error: Invalid module item.
/app/tb_tmp.sv:87: syntax error
/app/tb_tmp.sv:87: error: Invalid module item.
/app/tb_tmp.sv:90: syntax error
/app/tb_tmp.sv:90: error: Invalid module item.
/app/tb_tmp.sv:92: syntax error
/app/tb_tmp.sv:92: error: Invalid module instantiation
/app/tb_tmp.sv:93: error: Invalid module instantiation
/app/tb_tmp.sv:95: syntax error
/app/tb_tmp.sv:95: error: Invalid module item.
/app/tb_tmp.sv:97: syntax error
/app/tb_tmp.sv:97: error: Invalid module instantiation
/app/tb_tmp.sv:99: syntax error
/app/tb_tmp.sv:99: error: Invalid module item.
/app/tb_tmp.sv:102: syntax error
/app/tb_tmp.sv:102: error: Invalid module item.
/app/tb_tmp.sv:105: syntax error
/app/tb_tmp.sv:105: error: Invalid module item.
/app/tb_tmp.sv:108: syntax error
/app/tb_tmp.sv:108: error: Invalid module item.
/app/tb_tmp.sv:110: syntax error
/app/tb_tmp.sv:110: error: Invalid module instantiation
/app/tb_tmp.sv:111: error: Invalid module instantiation
/app/tb_tmp.sv:113: syntax error
/app/tb_tmp.sv:113: error: Invalid module instantiation
/app/tb_tmp.sv:114: error: Invalid module item.
/app/tb_tmp.sv:115: syntax error
/app/tb_tmp.sv:115: error: Invalid module item.
/app/tb_tmp.sv:117: syntax error
/app/tb_tmp.sv:117: error: Invalid module instantiation
/app/tb_tmp.sv:118: error: Invalid module instantiation
/app/tb_tmp.sv:119: error: Invalid module instantiation
/app/tb_tmp.sv:121: syntax error
/app/tb_tmp.sv:121: error: Invalid module item.
/app/tb_tmp.sv:123: syntax error
/app/tb_tmp.sv:123: error: Invalid module instantiation
/app/tb_tmp.sv:125: syntax error
/app/tb_tmp.sv:125: error: Invalid module item.
/app/tb_tmp.sv:128: syntax error
/app/tb_tmp.sv:128: error: Invalid module item.
/app/tb_tmp.sv:131: syntax error
/app/tb_tmp.sv:131: error: Invalid module item.
/app/tb_tmp.sv:134: syntax error
/app/tb_tmp.sv:134: error: Invalid module item.
/app/tb_tmp.sv:136: syntax error
/app/tb_tmp.sv:136: error: Invalid module instantiation
/app/tb_tmp.sv:137: error: Invalid module instantiation
/app/tb_tmp.sv:138: error: Invalid module instantiation
/app/tb_tmp.sv:139: error: Invalid module instantiation
/app/tb_tmp.sv:141: syntax error
/app/tb_tmp.sv:141: error: Invalid module instantiation
/app/tb_tmp.sv:144: syntax error
/app/tb_tmp.sv:144: error: Invalid module item.
/app/tb_tmp.sv:147: syntax error
/app/tb_tmp.sv:147: error: Invalid module item.
/app/tb_tmp.sv:150: syntax error
/app/tb_tmp.sv:150: error: Invalid module item.
/app/tb_tmp.sv:154: syntax error
I give up.
The DUT still compiles; the temporary testbench used a SystemVerilog task argument form this `iverilog` build does not accept. I’m adjusting only the testbench harness syntax and rerunning.
shell
nl -ba /app/tb_tmp.sv | sed -n '35,55p'
output
Chunk ID: cb7d92
Wall time: 0.0000 seconds
Process exited with code 0
Original token count: 250
Output:
    35	    task automatic tick;
    36	        begin
    37	            @(posedge clk);
    38	            #1;
    39	        end
    40	    endtask
    41	
    42	    task automatic expect(input logic exp_ack,
    43	                          input logic exp_busy,
    44	                          input logic exp_al,
    45	                          input logic exp_bit_out,
    46	                          input logic exp_scl_low,
    47	                          input logic exp_sda_low,
    48	                          input string label);
    49	        begin
    50	            if ({cmd_ack, busy, al, bit_out, scl_drive_low, sda_drive_low} !==
    51	                {exp_ack, exp_busy, exp_al, exp_bit_out, exp_scl_low, exp_sda_low}) begin
    52	                $display("FAIL %s: got ack=%0b busy=%0b al=%0b bit=%0b scl=%0b sda=%0b",
    53	                         label, cmd_ack, busy, al, bit_out, scl_drive_low, sda_drive_low);
    54	                $finish;
    55	            end
The issue is `expect` being treated as a SystemVerilog keyword by this toolchain. I’m renaming that temporary task and keeping the DUT untouched.
shell
perl -0pi -e 's/task automatic expect/task automatic check_outputs/g; s/\bexpect\(/check_outputs(/g' /app/tb_tmp.sv
output
Chunk ID: c1091b
Wall time: 0.0000 seconds
Process exited with code 0
Original token count: 0
Output:
shell
iverilog -g2012 -Wall -o /tmp/dut_tb.vvp /app/dut.sv /app/tb_tmp.sv
output
Chunk ID: 9cd561
Wall time: 0.0000 seconds
Process exited with code 0
Original token count: 0
Output:
shell
vvp /tmp/dut_tb.vvp
output
Chunk ID: 55fdfc
Wall time: 0.0000 seconds
Process exited with code 0
Original token count: 13
Output:
PASS
/app/tb_tmp.sv:153: $finish called at 266 (1s)
The temporary simulation passed. I’m removing the temporary testbench now and leaving only `/app/dut.sv`.
apply_patch
*** Begin Patch
*** Delete File: /app/tb_tmp.sv
*** End Patch


Exit code: 0
Wall time: 0 seconds
Output:
Success. Updated the following files:
D /app/tb_tmp.sv
shell
iverilog -g2012 -Wall -tnull /app/dut.sv
output
Chunk ID: a6d03e
Wall time: 0.0000 seconds
Process exited with code 0
Original token count: 0
Output:
shell
ls -la /app && nl -ba /app/dut.sv | sed -n '1,260p'
output
Chunk ID: e21932
Wall time: 0.0000 seconds
Process exited with code 0
Original token count: 2438
Output:
total 20
drwxr-xr-x 1 root root 4096 Jun 20 17:17 .
drwxr-xr-x 1 root root 4096 Jun 20 17:12 ..
-rw-r--r-- 1 root root 9449 Jun 20 17:16 dut.sv
     1	module TopModule (
     2	    input  logic       clk,
     3	    input  logic       rst,
     4	    input  logic       cmd_valid,
     5	    input  logic       bit_in,
     6	    input  logic       scl_i,
     7	    input  logic       sda_i,
     8	    input  logic [1:0] cmd,
     9	    output logic       cmd_ack,
    10	    output logic       busy,
    11	    output logic       al,
    12	    output logic       bit_out,
    13	    output logic       scl_drive_low,
    14	    output logic       sda_drive_low
    15	);
    16	
    17	    I2cBitController controller (
    18	        .clk(clk),
    19	        .rst(rst),
    20	        .cmd_valid(cmd_valid),
    21	        .bit_in(bit_in),
    22	        .scl_i(scl_i),
    23	        .sda_i(sda_i),
    24	        .cmd(cmd),
    25	        .cmd_ack(cmd_ack),
    26	        .busy(busy),
    27	        .al(al),
    28	        .bit_out(bit_out),
    29	        .scl_drive_low(scl_drive_low),
    30	        .sda_drive_low(sda_drive_low)
    31	    );
    32	
    33	endmodule
    34	
    35	module I2cBitController (
    36	    input  logic       clk,
    37	    input  logic       rst,
    38	    input  logic       cmd_valid,
    39	    input  logic       bit_in,
    40	    input  logic       scl_i,
    41	    input  logic       sda_i,
    42	    input  logic [1:0] cmd,
    43	    output logic       cmd_ack,
    44	    output logic       busy,
    45	    output logic       al,
    46	    output logic       bit_out,
    47	    output logic       scl_drive_low,
    48	    output logic       sda_drive_low
    49	);
    50	
    51	    localparam logic [1:0] CMD_START = 2'd0;
    52	    localparam logic [1:0] CMD_STOP  = 2'd1;
    53	    localparam logic [1:0] CMD_WRITE = 2'd2;
    54	    localparam logic [1:0] CMD_READ  = 2'd3;
    55	
    56	    typedef enum logic [4:0] {
    57	        ST_READY,
    58	        ST_START_ACCEPT,
    59	        ST_START_WAIT,
    60	        ST_START_SEEN,
    61	        ST_START_SDA_LOW,
    62	        ST_START_ACK,
    63	        ST_STOP_ACCEPT,
    64	        ST_STOP_SETUP,
    65	        ST_STOP_WAIT,
    66	        ST_STOP_SEEN,
    67	        ST_STOP_ACK,
    68	        ST_WRITE_ACCEPT,
    69	        ST_WRITE_SETUP,
    70	        ST_WRITE_WAIT,
    71	        ST_WRITE_SEEN,
    72	        ST_WRITE_ACK,
    73	        ST_READ_ACCEPT,
    74	        ST_READ_SETUP,
    75	        ST_READ_WAIT,
    76	        ST_READ_SEEN,
    77	        ST_READ_ACK
    78	    } state_t;
    79	
    80	    state_t state;
    81	    logic write_bit;
    82	
    83	    function automatic logic command_is_legal(input logic [1:0] command,
    84	                                              input logic is_busy);
    85	        command_is_legal = (command == CMD_START) || is_busy;
    86	    endfunction
    87	
    88	    task automatic hold_lines;
    89	        begin
    90	            scl_drive_low <= scl_drive_low;
    91	            sda_drive_low <= sda_drive_low;
    92	        end
    93	    endtask
    94	
    95	    task automatic accept_command;
    96	        begin
    97	            case (cmd)
    98	                CMD_START: begin
    99	                    state         <= ST_START_ACCEPT;
   100	                    busy          <= 1'b1;
   101	                    scl_drive_low <= 1'b0;
   102	                    sda_drive_low <= 1'b0;
   103	                end
   104	
   105	                CMD_STOP: begin
   106	                    state         <= ST_STOP_ACCEPT;
   107	                    scl_drive_low <= 1'b1;
   108	                    sda_drive_low <= 1'b1;
   109	                end
   110	
   111	                CMD_WRITE: begin
   112	                    state         <= ST_WRITE_ACCEPT;
   113	                    write_bit     <= bit_in;
   114	                    scl_drive_low <= 1'b1;
   115	                    sda_drive_low <= ~bit_in;
   116	                end
   117	
   118	                CMD_READ: begin
   119	                    state         <= ST_READ_ACCEPT;
   120	                    scl_drive_low <= 1'b1;
   121	                    sda_drive_low <= 1'b0;
   122	                end
   123	
   124	                default: begin
   125	                    state <= ST_READY;
   126	                end
   127	            endcase
   128	
   129	            cmd_ack <= 1'b0;
   130	        end
   131	    endtask
   132	
   133	    always_ff @(posedge clk) begin
   134	        if (rst) begin
   135	            state         <= ST_READY;
   136	            write_bit     <= 1'b0;
   137	            cmd_ack       <= 1'b0;
   138	            busy          <= 1'b0;
   139	            al            <= 1'b0;
   140	            bit_out       <= 1'b0;
   141	            scl_drive_low <= 1'b0;
   142	            sda_drive_low <= 1'b0;
   143	        end else begin
   144	            cmd_ack <= 1'b0;
   145	
   146	            case (state)
   147	                ST_READY: begin
   148	                    if (cmd_valid && command_is_legal(cmd, busy)) begin
   149	                        accept_command();
   150	                    end
   151	                end
   152	
   153	                ST_START_ACCEPT: begin
   154	                    state         <= ST_START_WAIT;
   155	                    scl_drive_low <= 1'b0;
   156	                    sda_drive_low <= 1'b0;
   157	                end
   158	
   159	                ST_START_WAIT: begin
   160	                    scl_drive_low <= 1'b0;
   161	                    sda_drive_low <= 1'b0;
   162	                    if (scl_i) begin
   163	                        state <= ST_START_SEEN;
   164	                        if (!sda_i) begin
   165	                            al <= 1'b1;
   166	                        end
   167	                    end
   168	                end
   169	
   170	                ST_START_SEEN: begin
   171	                    state         <= ST_START_SDA_LOW;
   172	                    scl_drive_low <= 1'b0;
   173	                    sda_drive_low <= 1'b1;
   174	                    if (scl_i && !sda_i) begin
   175	                        al <= 1'b1;
   176	                    end
   177	                end
   178	
   179	                ST_START_SDA_LOW: begin
   180	                    state         <= ST_START_ACK;
   181	                    scl_drive_low <= 1'b1;
   182	                    sda_drive_low <= 1'b1;
   183	                    cmd_ack       <= 1'b1;
   184	                end
   185	
   186	                ST_START_ACK: begin
   187	                    if (cmd_valid && command_is_legal(cmd, busy)) begin
   188	                        accept_command();
   189	                    end else begin
   190	                        state <= ST_READY;
   191	                    end
   192	                end
   193	
   194	                ST_STOP_ACCEPT: begin
   195	                    state         <= ST_STOP_SETUP;
   196	                    scl_drive_low <= 1'b1;
   197	                    sda_drive_low <= 1'b1;
   198	                end
   199	
   200	                ST_STOP_SETUP: begin
   201	                    state         <= ST_STOP_WAIT;
   202	                    scl_drive_low <= 1'b0;
   203	                    sda_drive_low <= 1'b1;
   204	                end
   205	
   206	                ST_STOP_WAIT: begin
   207	                    scl_drive_low <= 1'b0;
   208	                    sda_drive_low <= 1'b1;
   209	                    if (scl_i) begin
   210	                        state <= ST_STOP_SEEN;
   211	                    end
   212	                end
   213	
   214	                ST_STOP_SEEN: begin
   215	                    state         <= ST_STOP_ACK;
   216	                    busy          <= 1'b0;
   217	                    scl_drive_low <= 1'b0;
   218	                    sda_drive_low <= 1'b0;
   219	                    cmd_ack       <= 1'b1;
   220	                end
   221	
   222	                ST_STOP_ACK: begin
   223	                    if (cmd_valid && command_is_legal(cmd, 1'b0)) begin
   224	                        accept_command();
   225	                    end else begin
   226	                        state <= ST_READY;
   227	                    end
   228	                end
   229	
   230	                ST_WRITE_ACCEPT: begin
   231	                    state         <= ST_WRITE_SETUP;
   232	                    scl_drive_low <= 1'b1;
   233	                    sda_drive_low <= ~write_bit;
   234	                end
   235	
   236	                ST_WRITE_SETUP: begin
   237	                    state         <= ST_WRITE_WAIT;
   238	                    scl_drive_low <= 1'b0;
   239	                    sda_drive_low <= ~write_bit;
   240	                end
   241	
   242	                ST_WRITE_WAIT: begin
   243	                    scl_drive_low <= 1'b0;
   244	                    sda_drive_low <= ~write_bit;
   245	                    if (scl_i) begin
   246	                        state <= ST_WRITE_SEEN;
   247	                        if (write_bit && !sda_i) begin
   248	                            al <= 1'b1;
   249	                        end
   250	                    end
   251	                end
   252	
   253	                ST_WRITE_SEEN: begin
   254	                    state         <= ST_WRITE_ACK;
   255	                    scl_drive_low <= 1'b1;
   256	                    sda_drive_low <= ~write_bit;
   257	                    cmd_ack       <= 1'b1;
   258	                    if (scl_i && write_bit && !sda_i) begin
   259	                        al <= 1'b1;
   260	                    end
`dut.sv` still passes `iverilog -g2012 -Wall`, and the temp harness has been removed. I’m doing one last read over the final file for unnecessary scaffolding before closing out.
shell
nl -ba /app/dut.sv | sed -n '261,360p'
output
Chunk ID: 81141a
Wall time: 0.0000 seconds
Process exited with code 0
Original token count: 513
Output:
   261	                end
   262	
   263	                ST_WRITE_ACK: begin
   264	                    if (cmd_valid && command_is_legal(cmd, busy)) begin
   265	                        accept_command();
   266	                    end else begin
   267	                        state <= ST_READY;
   268	                    end
   269	                end
   270	
   271	                ST_READ_ACCEPT: begin
   272	                    state         <= ST_READ_SETUP;
   273	                    scl_drive_low <= 1'b1;
   274	                    sda_drive_low <= 1'b0;
   275	                end
   276	
   277	                ST_READ_SETUP: begin
   278	                    state         <= ST_READ_WAIT;
   279	                    scl_drive_low <= 1'b0;
   280	                    sda_drive_low <= 1'b0;
   281	                end
   282	
   283	                ST_READ_WAIT: begin
   284	                    scl_drive_low <= 1'b0;
   285	                    sda_drive_low <= 1'b0;
   286	                    if (scl_i) begin
   287	                        state   <= ST_READ_SEEN;
   288	                        bit_out <= sda_i;
   289	                    end
   290	                end
   291	
   292	                ST_READ_SEEN: begin
   293	                    state         <= ST_READ_ACK;
   294	                    scl_drive_low <= 1'b1;
   295	                    sda_drive_low <= 1'b0;
   296	                    cmd_ack       <= 1'b1;
   297	                end
   298	
   299	                ST_READ_ACK: begin
   300	                    if (cmd_valid && command_is_legal(cmd, busy)) begin
   301	                        accept_command();
   302	                    end else begin
   303	                        state <= ST_READY;
   304	                    end
   305	                end
   306	
   307	                default: begin
   308	                    state <= ST_READY;
   309	                    hold_lines();
   310	                end
   311	            endcase
   312	        end
   313	    end
   314	
   315	endmodule
There’s one small cleanup: a default-state helper task only self-assigned the line outputs and is not needed. I’m removing that dead scaffolding while preserving the same behavior.
apply_patch
*** Begin Patch
*** Update File: /app/dut.sv
@@
-    task automatic hold_lines;
-        begin
-            scl_drive_low <= scl_drive_low;
-            sda_drive_low <= sda_drive_low;
-        end
-    endtask
-
     task automatic accept_command;
         begin
@@
                 default: begin
                     state <= ST_READY;
-                    hold_lines();
                 end
             endcase
*** End Patch


Exit code: 0
Wall time: 0 seconds
Output:
Success. Updated the following files:
M /app/dut.sv
The cleanup is in. I’m running the final syntax check now.
shell
iverilog -g2012 -Wall -tnull /app/dut.sv
output
Chunk ID: 5d8f29
Wall time: 0.0000 seconds
Process exited with code 0
Original token count: 0
Output:
shell
ls -la /app
output
Chunk ID: 0b2983
Wall time: 0.0000 seconds
Process exited with code 0
Original token count: 36
Output:
total 20
drwxr-xr-x 1 root root 4096 Jun 20 17:17 .
drwxr-xr-x 1 root root 4096 Jun 20 17:12 ..
-rw-r--r-- 1 root root 9257 Jun 20 17:17 dut.sv
Implemented [dut.sv](/app/dut.sv:1). What changed: - Added `TopModule` with the requested ports. - Added and instantiated `I2cBitController`. - Implemented registered outputs, synchronous active-high reset, open-drain drive controls, legal command gating, one-cycle `cmd_ack`, sticky `al`, read sampling, and the required registered phase delays. Verification: - `iverilog -g2012 -Wall -tnull /app/dut.sv` passes. - Ran a temporary self-checking simulation for reset, illegal idle command, start/stop/read/write timing, post-ack accept, and sticky arbitration lost behavior; it passed.
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
MISMATCH_COUNTS cmd_ack=108 busy=0 al=582 bit_out=0 scl=54 sda=54
__CHIPBENCH_MISMATCH_SUMMARY__: mismatches=798 samples=2351

Reproduce this trial: git checkout 2f94510 && PYTHONPATH=src python3 scripts/build_site.py , then open trial/trial_4bce4783740943ec. Re-running the agent live requires EVAL_PLATFORM_ENABLE_OAUTH_SMOKE=1 and is non-deterministic.

Trial trial_4bce4783740943ec · verifier authoritative; classifier explanatory.