SyncValsverifier → artifact → classifier → verdict
SyncVals · Trajectory

open-drain-command-engine

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.
SubtypeIncomplete Understanding
EvidenceTest output: 'MISMATCH_COUNTS al=116' indicating 116 arbitration loss signal mismatches across 2351 samples. The agent's `al` logic checks external `sda_i` observation but fails to correctly correlate it with the "released SDA" state (sda_drive_low=0). Instruction requires: 'al is sticky until reset and asserts only during start or write-1 high-SCL phases when released SDA is observed low.' Agent's implementation in ST_START_WAIT, ST_START_SDA_LOW_LOAD, ST_WRITE_WAIT, and ST_WRITE_DONE_LOAD states does not properly validate that SDA was released before asserting arbitration loss.
Root causeThe agent understood the overall I2C command engine structure and implemented a detailed 16-state FSM covering timing phases, but failed to correctly interpret the "released SDA observed low" arbitration loss condition. The logic checks external SDA input but doesn't validate the precondition that the controller itself released SDA (sda_drive_low=0), leading to incorrect al signal generation.
RecommendationN/A - task is fine
Trajectory
Tool-by-tool agent trajectory
7 tool calls · 2 tool types · 16 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 existing `dut.sv` before editing, then implement the state machine directly around the timing constraints you specified.
shell
ls && rg --files -g 'dut.sv' -g '*.sv' -g '*.v' -g '*test*' -g '*tb*'
output
Chunk ID: 0d92f6
Wall time: 0.0000 seconds
Process exited with code 1
Original token count: 0
Output:
The first listing didn’t show files, so I’m checking the directory contents more explicitly before creating or replacing `/app/dut.sv`.
shell
pwd; ls -la; find . -maxdepth 2 -type f | sort | head -100
output
Chunk ID: 6aff11
Wall time: 0.0001 seconds
Process exited with code 0
Original token count: 25
Output:
/app
total 8
drwxr-xr-x 2 root root 4096 Jun 19 22:02 .
drwxr-xr-x 1 root root 4096 Jun 20 16:42 ..
I’m going to create `dut.sv` with a small wrapper `TopModule` and an instantiated controller module. The controller will use explicit “visible phase” states so command accept, setup, SCL wait, sample, and ack each land on separate registered clock edges.
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
+);
+
+    i2c_bit_controller 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 i2c_bit_controller (
+    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 [3:0] {
+        ST_IDLE,
+        ST_START_WAIT,
+        ST_START_SDA_LOW_LOAD,
+        ST_START_SDA_LOW,
+        ST_STOP_SETUP,
+        ST_STOP_RELEASE_LOAD,
+        ST_STOP_WAIT,
+        ST_STOP_DONE_LOAD,
+        ST_WRITE_SETUP,
+        ST_WRITE_RELEASE_LOAD,
+        ST_WRITE_WAIT,
+        ST_WRITE_DONE_LOAD,
+        ST_READ_SETUP,
+        ST_READ_RELEASE_LOAD,
+        ST_READ_WAIT,
+        ST_READ_DONE_LOAD
+    } state_t;
+
+    state_t state;
+    logic write_bit;
+
+    always_ff @(posedge clk) begin
+        if (rst) begin
+            state         <= ST_IDLE;
+            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;
+
+            unique case (state)
+                ST_IDLE: begin
+                    if (cmd_valid) begin
+                        unique case (cmd)
+                            CMD_START: begin
+                                busy          <= 1'b1;
+                                scl_drive_low <= 1'b0;
+                                sda_drive_low <= 1'b0;
+                                state         <= ST_START_WAIT;
+                            end
+
+                            CMD_STOP: begin
+                                if (busy) begin
+                                    scl_drive_low <= 1'b1;
+                                    sda_drive_low <= 1'b1;
+                                    state         <= ST_STOP_SETUP;
+                                end
+                            end
+
+                            CMD_WRITE: begin
+                                if (busy) begin
+                                    write_bit     <= bit_in;
+                                    scl_drive_low <= 1'b1;
+                                    sda_drive_low <= ~bit_in;
+                                    state         <= ST_WRITE_SETUP;
+                                end
+                            end
+
+                            CMD_READ: begin
+                                if (busy) begin
+                                    scl_drive_low <= 1'b1;
+                                    sda_drive_low <= 1'b0;
+                                    state         <= ST_READ_SETUP;
+                                end
+                            end
+
+                            default: begin
+                                state <= ST_IDLE;
+                            end
+                        endcase
+                    end
+                end
+
+                ST_START_WAIT: begin
+                    scl_drive_low <= 1'b0;
+                    sda_drive_low <= 1'b0;
+                    if (scl_i) begin
+                        if (!sda_i) begin
+                            al <= 1'b1;
+                        end
+                        state <= ST_START_SDA_LOW_LOAD;
+                    end
+                end
+
+                ST_START_SDA_LOW_LOAD: begin
+                    if (scl_i && !sda_i) begin
+                        al <= 1'b1;
+                    end
+                    scl_drive_low <= 1'b0;
+                    sda_drive_low <= 1'b1;
+                    state         <= ST_START_SDA_LOW;
+                end
+
+                ST_START_SDA_LOW: begin
+                    scl_drive_low <= 1'b1;
+                    sda_drive_low <= 1'b1;
+                    cmd_ack       <= 1'b1;
+                    state         <= ST_IDLE;
+                end
+
+                ST_STOP_SETUP: begin
+                    scl_drive_low <= 1'b1;
+                    sda_drive_low <= 1'b1;
+                    state         <= ST_STOP_RELEASE_LOAD;
+                end
+
+                ST_STOP_RELEASE_LOAD: begin
+                    scl_drive_low <= 1'b0;
+                    sda_drive_low <= 1'b1;
+                    state         <= ST_STOP_WAIT;
+                end
+
+                ST_STOP_WAIT: begin
+                    scl_drive_low <= 1'b0;
+                    sda_drive_low <= 1'b1;
+                    if (scl_i) begin
+                        state <= ST_STOP_DONE_LOAD;
+                    end
+                end
+
+                ST_STOP_DONE_LOAD: begin
+                    scl_drive_low <= 1'b0;
+                    sda_drive_low <= 1'b0;
+                    busy          <= 1'b0;
+                    cmd_ack       <= 1'b1;
+                    state         <= ST_IDLE;
+                end
+
+                ST_WRITE_SETUP: begin
+                    scl_drive_low <= 1'b1;
+                    sda_drive_low <= ~write_bit;
+                    state         <= ST_WRITE_RELEASE_LOAD;
+                end
+
+                ST_WRITE_RELEASE_LOAD: begin
+                    scl_drive_low <= 1'b0;
+                    sda_drive_low <= ~write_bit;
+                    state         <= ST_WRITE_WAIT;
+                end
+
+                ST_WRITE_WAIT: begin
+                    scl_drive_low <= 1'b0;
+                    sda_drive_low <= ~write_bit;
+                    if (scl_i) begin
+                        if (write_bit && !sda_i) begin
+                            al <= 1'b1;
+                        end
+                        state <= ST_WRITE_DONE_LOAD;
+                    end
+                end
+
+                ST_WRITE_DONE_LOAD: begin
+                    if (write_bit && scl_i && !sda_i) begin
+                        al <= 1'b1;
+                    end
+                    scl_drive_low <= 1'b1;
+                    sda_drive_low <= ~write_bit;
+                    cmd_ack       <= 1'b1;
+                    state         <= ST_IDLE;
+                end
+
+                ST_READ_SETUP: begin
+                    scl_drive_low <= 1'b1;
+                    sda_drive_low <= 1'b0;
+                    state         <= ST_READ_RELEASE_LOAD;
+                end
+
+                ST_READ_RELEASE_LOAD: begin
+                    scl_drive_low <= 1'b0;
+                    sda_drive_low <= 1'b0;
+                    state         <= ST_READ_WAIT;
+                end
+
+                ST_READ_WAIT: begin
+                    scl_drive_low <= 1'b0;
+                    sda_drive_low <= 1'b0;
+                    if (scl_i) begin
+                        bit_out <= sda_i;
+                        state   <= ST_READ_DONE_LOAD;
+                    end
+                end
+
+                ST_READ_DONE_LOAD: begin
+                    scl_drive_low <= 1'b1;
+                    sda_drive_low <= 1'b0;
+                    cmd_ack       <= 1'b1;
+                    state         <= ST_IDLE;
+                end
+
+                default: begin
+                    state <= ST_IDLE;
+                end
+            endcase
+        end
+    end
+
+endmodule
*** End Patch


Exit code: 0
Wall time: 0 seconds
Output:
Success. Updated the following files:
A /app/dut.sv
`dut.sv` is in place. I’m doing a syntax pass now and will adjust if the local simulator has stricter SystemVerilog support than expected.
shell
command -v verilator || true
output
Chunk ID: 60d76f
Wall time: 0.0000 seconds
Process exited with code 0
Original token count: 0
Output:
shell
command -v iverilog || true
output
Chunk ID: 3f58ae
Wall time: 0.0000 seconds
Process exited with code 0
Original token count: 5
Output:
/usr/bin/iverilog
shell
sed -n '1,260p' /app/dut.sv
output
Chunk ID: a87f31
Wall time: 0.0000 seconds
Process exited with code 0
Original token count: 2074
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
);

    i2c_bit_controller 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 i2c_bit_controller (
    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 [3:0] {
        ST_IDLE,
        ST_START_WAIT,
        ST_START_SDA_LOW_LOAD,
        ST_START_SDA_LOW,
        ST_STOP_SETUP,
        ST_STOP_RELEASE_LOAD,
        ST_STOP_WAIT,
        ST_STOP_DONE_LOAD,
        ST_WRITE_SETUP,
        ST_WRITE_RELEASE_LOAD,
        ST_WRITE_WAIT,
        ST_WRITE_DONE_LOAD,
        ST_READ_SETUP,
        ST_READ_RELEASE_LOAD,
        ST_READ_WAIT,
        ST_READ_DONE_LOAD
    } state_t;

    state_t state;
    logic write_bit;

    always_ff @(posedge clk) begin
        if (rst) begin
            state         <= ST_IDLE;
            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;

            unique case (state)
                ST_IDLE: begin
                    if (cmd_valid) begin
                        unique case (cmd)
                            CMD_START: begin
                                busy          <= 1'b1;
                                scl_drive_low <= 1'b0;
                                sda_drive_low <= 1'b0;
                                state         <= ST_START_WAIT;
                            end

                            CMD_STOP: begin
                                if (busy) begin
                                    scl_drive_low <= 1'b1;
                                    sda_drive_low <= 1'b1;
                                    state         <= ST_STOP_SETUP;
                                end
                            end

                            CMD_WRITE: begin
                                if (busy) begin
                                    write_bit     <= bit_in;
                                    scl_drive_low <= 1'b1;
                                    sda_drive_low <= ~bit_in;
                                    state         <= ST_WRITE_SETUP;
                                end
                            end

                            CMD_READ: begin
                                if (busy) begin
                                    scl_drive_low <= 1'b1;
                                    sda_drive_low <= 1'b0;
                                    state         <= ST_READ_SETUP;
                                end
                            end

                            default: begin
                                state <= ST_IDLE;
                            end
                        endcase
                    end
                end

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

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

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

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

                ST_STOP_RELEASE_LOAD: begin
                    scl_drive_low <= 1'b0;
                    sda_drive_low <= 1'b1;
                    state         <= ST_STOP_WAIT;
                end

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

                ST_STOP_DONE_LOAD: begin
                    scl_drive_low <= 1'b0;
                    sda_drive_low <= 1'b0;
                    busy          <= 1'b0;
                    cmd_ack       <= 1'b1;
                    state         <= ST_IDLE;
                end

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

                ST_WRITE_RELEASE_LOAD: begin
                    scl_drive_low <= 1'b0;
                    sda_drive_low <= ~write_bit;
                    state         <= ST_WRITE_WAIT;
                end

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

                ST_WRITE_DONE_LOAD: begin
                    if (write_bit && scl_i && !sda_i) begin
                        al <= 1'b1;
                    end
                    scl_drive_low <= 1'b1;
                    sda_drive_low <= ~write_bit;
                    cmd_ack       <= 1'b1;
                    state         <= ST_IDLE;
                end

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

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

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

                ST_READ_DONE_LOAD: begin
                    scl_drive_low <= 1'b1;
                    sda_drive_low <= 1'b0;
                    cmd_ack       <= 1'b1;
                    state         <= ST_IDLE;
                end

                default: begin
                    state <= ST_IDLE;
                end
            endcase
        end
    end

endmodule
Only `iverilog` is available here, so I’ll use it with SystemVerilog enabled for the compile check.
shell
iverilog -g2012 -Wall -tnull /app/dut.sv
output
Chunk ID: 171f00
Wall time: 0.0000 seconds
Process exited with code 0
Original token count: 0
Output:
Implemented [dut.sv](/app/dut.sv) with `TopModule` plus an instantiated `i2c_bit_controller`. Key points covered: - Synchronous active-high reset clears all registered outputs. - Registered `cmd_ack` one-cycle completion pulse. - Legal command acceptance only from inactive state, with `cmd=0` allowed before/after ownership and other commands only while `busy`. - Open-drain line drive semantics. - Explicit phase states for accept/setup/SCL-wait/sample/ack timing. - Sticky `al` for start and write-1 high-SCL arbitration loss cases. Verified with: ```bash iverilog -g2012 -Wall -tnull /app/dut.sv ```
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=0 busy=0 al=116 bit_out=0 scl=0 sda=0
__CHIPBENCH_MISMATCH_SUMMARY__: mismatches=116 samples=2351

Reproduce this trial: git checkout 2f94510 && PYTHONPATH=src python3 scripts/build_site.py , then open trial/trial_cefe932f03244976. Re-running the agent live requires EVAL_PLATFORM_ENABLE_OAUTH_SMOKE=1 and is non-deterministic.

Trial trial_cefe932f03244976 · verifier authoritative; classifier explanatory.