SyncValsverifier → artifact → classifier → verdict
SyncVals · Trajectory

open-drain-command-engine

codex gpt-5.5 ✓ resolved GOOD_SUCCESS ↑ View task
Solved from the instruction alone, tests/ and solution/ were withheld from the agent's workspace and restored only for grading.
Reward = tests/test.sh exit code (0 → resolved); the classification below is post-hoc and cannot change it.
Classification , post-hoc; cannot change the reward
GOOD_SUCCESSLegitimate solve, implements the asked-for behavior; tests verify real functionality.
SubtypeLegitimate Solution
EvidenceTest output shows 'mismatches=0 samples=2351' with reward=1.0. Agent implemented TopModule with instantiated I2cBitCommandEngine using explicit state machine with 16 states (ST_READY, ST_START_WAIT_SCL, ST_START_SDA_LOW, ST_START_FINISH, ST_STOP_SETUP, ST_STOP_RELEASE_SCL, ST_STOP_WAIT_SCL, ST_STOP_FINISH, ST_WRITE_SETUP, ST_WRITE_RELEASE_SCL, ST_WRITE_WAIT_SCL, ST_WRITE_FINISH, ST_READ_SETUP, ST_READ_RELEASE_SCL, ST_READ_WAIT_SCL, ST_READ_FINISH). All outputs registered with synchronous reset. Agent verified via: (1) iverilog syntax check, (2) custom testbench checking phase timing for start/write/read/stop commands. Temporary testbench output: 'PASS'.
Root causeAgent correctly interpreted a dense, complex I2C timing specification and implemented a complete, correct state machine that perfectly passes comprehensive verification tests with zero mismatches across 2351 samples.
RecommendationN/A - task is fine
Trajectory
Tool-by-tool agent trajectory
13 tool calls · 2 tool types · 29 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 I’ll implement the state machine and run a syntax check if a Verilog tool is available.
shell
pwd && rg --files -n /app | head -100 && sed -n '1,240p' /app/dut.sv
output
Chunk ID: e197b0
Wall time: 0.0000 seconds
Process exited with code 2
Original token count: 15
Output:
/app
sed: can't read /app/dut.sv: No such file or directory
`/app/dut.sv` does not exist yet, so I’m checking the directory shape and then I’ll create it with the required two-module structure.
shell
ls -la /app
output
Chunk ID: 27bed1
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 16:53 ..
shell
find /app -maxdepth 2 -type f | sort | sed -n '1,120p'
output
Chunk ID: 296445
Wall time: 0.0000 seconds
Process exited with code 0
Original token count: 0
Output:
I’ve got the key timing constraint now: each accepted command becomes its own visible registered phase, and high-SCL observations advance only to the next visible phase one clock later. I’m encoding that directly as explicit phase states rather than collapsing waits into the accept edge.
I’m going to create `/app/dut.sv` now. The structure will be a thin `TopModule` wrapper plus a registered command engine module with explicit states for accept, setup, wait, and completion phases.
apply_patch
*** Begin Patch
*** Add File: /app/dut.sv
+module TopModule (
+    input clk,
+    input rst,
+    input cmd_valid,
+    input bit_in,
+    input scl_i,
+    input sda_i,
+    input [1:0] cmd,
+    output cmd_ack,
+    output busy,
+    output al,
+    output bit_out,
+    output scl_drive_low,
+    output sda_drive_low
+);
+
+    I2cBitCommandEngine engine (
+        .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 I2cBitCommandEngine (
+    input clk,
+    input rst,
+    input cmd_valid,
+    input bit_in,
+    input scl_i,
+    input sda_i,
+    input [1:0] cmd,
+    output reg cmd_ack,
+    output reg busy,
+    output reg al,
+    output reg bit_out,
+    output reg scl_drive_low,
+    output reg sda_drive_low
+);
+
+    localparam [1:0] CMD_START = 2'd0;
+    localparam [1:0] CMD_STOP  = 2'd1;
+    localparam [1:0] CMD_WRITE = 2'd2;
+    localparam [1:0] CMD_READ  = 2'd3;
+
+    localparam [3:0] ST_READY             = 4'd0;
+    localparam [3:0] ST_START_WAIT_SCL    = 4'd1;
+    localparam [3:0] ST_START_SDA_LOW     = 4'd2;
+    localparam [3:0] ST_START_FINISH      = 4'd3;
+    localparam [3:0] ST_STOP_SETUP        = 4'd4;
+    localparam [3:0] ST_STOP_RELEASE_SCL  = 4'd5;
+    localparam [3:0] ST_STOP_WAIT_SCL     = 4'd6;
+    localparam [3:0] ST_STOP_FINISH       = 4'd7;
+    localparam [3:0] ST_WRITE_SETUP       = 4'd8;
+    localparam [3:0] ST_WRITE_RELEASE_SCL = 4'd9;
+    localparam [3:0] ST_WRITE_WAIT_SCL    = 4'd10;
+    localparam [3:0] ST_WRITE_FINISH      = 4'd11;
+    localparam [3:0] ST_READ_SETUP        = 4'd12;
+    localparam [3:0] ST_READ_RELEASE_SCL  = 4'd13;
+    localparam [3:0] ST_READ_WAIT_SCL     = 4'd14;
+    localparam [3:0] ST_READ_FINISH       = 4'd15;
+
+    reg [3:0] state;
+    reg write_bit;
+
+    always @(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) begin
+                        case (cmd)
+                            CMD_START: begin
+                                busy <= 1'b1;
+                                scl_drive_low <= 1'b0;
+                                sda_drive_low <= 1'b0;
+                                state <= ST_START_WAIT_SCL;
+                            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
+                        endcase
+                    end
+                end
+
+                ST_START_WAIT_SCL: 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;
+                    end
+                end
+
+                ST_START_SDA_LOW: begin
+                    scl_drive_low <= 1'b0;
+                    sda_drive_low <= 1'b1;
+                    state <= ST_START_FINISH;
+                end
+
+                ST_START_FINISH: begin
+                    scl_drive_low <= 1'b1;
+                    sda_drive_low <= 1'b1;
+                    cmd_ack <= 1'b1;
+                    state <= ST_READY;
+                end
+
+                ST_STOP_SETUP: begin
+                    scl_drive_low <= 1'b1;
+                    sda_drive_low <= 1'b1;
+                    state <= ST_STOP_RELEASE_SCL;
+                end
+
+                ST_STOP_RELEASE_SCL: begin
+                    scl_drive_low <= 1'b0;
+                    sda_drive_low <= 1'b1;
+                    state <= ST_STOP_WAIT_SCL;
+                end
+
+                ST_STOP_WAIT_SCL: begin
+                    scl_drive_low <= 1'b0;
+                    sda_drive_low <= 1'b1;
+                    if (scl_i) begin
+                        state <= ST_STOP_FINISH;
+                    end
+                end
+
+                ST_STOP_FINISH: begin
+                    scl_drive_low <= 1'b0;
+                    sda_drive_low <= 1'b0;
+                    busy <= 1'b0;
+                    cmd_ack <= 1'b1;
+                    state <= ST_READY;
+                end
+
+                ST_WRITE_SETUP: begin
+                    scl_drive_low <= 1'b1;
+                    sda_drive_low <= ~write_bit;
+                    state <= ST_WRITE_RELEASE_SCL;
+                end
+
+                ST_WRITE_RELEASE_SCL: begin
+                    scl_drive_low <= 1'b0;
+                    sda_drive_low <= ~write_bit;
+                    state <= ST_WRITE_WAIT_SCL;
+                end
+
+                ST_WRITE_WAIT_SCL: 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_FINISH;
+                    end
+                end
+
+                ST_WRITE_FINISH: begin
+                    scl_drive_low <= 1'b1;
+                    sda_drive_low <= ~write_bit;
+                    cmd_ack <= 1'b1;
+                    state <= ST_READY;
+                end
+
+                ST_READ_SETUP: begin
+                    scl_drive_low <= 1'b1;
+                    sda_drive_low <= 1'b0;
+                    state <= ST_READ_RELEASE_SCL;
+                end
+
+                ST_READ_RELEASE_SCL: begin
+                    scl_drive_low <= 1'b0;
+                    sda_drive_low <= 1'b0;
+                    state <= ST_READ_WAIT_SCL;
+                end
+
+                ST_READ_WAIT_SCL: begin
+                    scl_drive_low <= 1'b0;
+                    sda_drive_low <= 1'b0;
+                    if (scl_i) begin
+                        bit_out <= sda_i;
+                        state <= ST_READ_FINISH;
+                    end
+                end
+
+                ST_READ_FINISH: begin
+                    scl_drive_low <= 1'b1;
+                    sda_drive_low <= 1'b0;
+                    cmd_ack <= 1'b1;
+                    state <= ST_READY;
+                end
+
+                default: begin
+                    state <= ST_READY;
+                end
+            endcase
+        end
+    end
+
+endmodule
*** End Patch


Exit code: 0
Wall time: 0 seconds
Output:
Success. Updated the following files:
A /app/dut.sv
The implementation is in place. I’m running a syntax check now, and if the simulator is available I’ll also exercise the phase timing with a small throwaway testbench.
shell
command -v iverilog || true
command -v verilator || true
output
Chunk ID: 328fa3
Wall time: 0.0000 seconds
Process exited with code 0
Original token count: 5
Output:
/usr/bin/iverilog
`iverilog` is available, so I’ll use that for the compile check and a focused simulation against the requested command timing.
shell
iverilog -g2012 -Wall -tnull /app/dut.sv
output
Chunk ID: fec5b3
Wall time: 0.0000 seconds
Process exited with code 0
Original token count: 0
Output:
The file compiles cleanly. I’m adding a temporary simulation testbench outside the submitted file to check the visible-cycle behavior around start, write, read, and stop.
apply_patch
*** Begin Patch
*** Add File: /tmp/tb_dut.sv
+`timescale 1ns/1ps
+
+module tb;
+    reg clk;
+    reg rst;
+    reg cmd_valid;
+    reg bit_in;
+    reg scl_i;
+    reg sda_i;
+    reg [1:0] cmd;
+    wire cmd_ack;
+    wire busy;
+    wire al;
+    wire bit_out;
+    wire scl_drive_low;
+    wire 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 tick;
+        begin
+            @(negedge clk);
+            @(posedge clk);
+            #1;
+        end
+    endtask
+
+    task expect;
+        input value;
+        input expected;
+        input [160*8-1:0] name;
+        begin
+            if (value !== expected) begin
+                $display("FAIL %0s got %0b expected %0b", name, value, expected);
+                $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();
+        rst = 1'b0;
+        tick();
+
+        cmd = 2'd0;
+        cmd_valid = 1'b1;
+        tick();
+        cmd_valid = 1'b0;
+        expect(busy, 1'b1, "start accept sets busy");
+        expect(scl_drive_low, 1'b0, "start accept releases scl");
+        expect(sda_drive_low, 1'b0, "start accept releases sda");
+        expect(cmd_ack, 1'b0, "start accept no ack");
+
+        tick();
+        expect(scl_drive_low, 1'b0, "start wait observes high only");
+        expect(sda_drive_low, 1'b0, "start wait holds sda release");
+        expect(cmd_ack, 1'b0, "start wait no ack");
+
+        tick();
+        expect(scl_drive_low, 1'b0, "start sda low holds scl release");
+        expect(sda_drive_low, 1'b1, "start sda low");
+        expect(cmd_ack, 1'b0, "start sda low no ack");
+
+        tick();
+        expect(scl_drive_low, 1'b1, "start finish pulls scl low");
+        expect(sda_drive_low, 1'b1, "start finish keeps sda low");
+        expect(cmd_ack, 1'b1, "start ack");
+
+        cmd = 2'd2;
+        bit_in = 1'b1;
+        cmd_valid = 1'b1;
+        tick();
+        cmd_valid = 1'b0;
+        expect(cmd_ack, 1'b0, "write accept clears ack");
+        expect(scl_drive_low, 1'b1, "write accept scl low");
+        expect(sda_drive_low, 1'b0, "write one releases sda");
+
+        tick();
+        expect(scl_drive_low, 1'b1, "write setup scl low");
+        expect(sda_drive_low, 1'b0, "write setup sda release");
+
+        tick();
+        expect(scl_drive_low, 1'b0, "write releases scl");
+        expect(sda_drive_low, 1'b0, "write high phase sda release");
+        expect(cmd_ack, 1'b0, "write release no ack");
+
+        sda_i = 1'b0;
+        tick();
+        expect(al, 1'b1, "write one arbitration lost");
+        expect(cmd_ack, 1'b0, "write high observe no ack");
+
+        tick();
+        expect(cmd_ack, 1'b1, "write ack after high observe");
+        expect(scl_drive_low, 1'b1, "write finish pulls scl low");
+
+        sda_i = 1'b1;
+        cmd = 2'd3;
+        cmd_valid = 1'b1;
+        tick();
+        cmd_valid = 1'b0;
+        expect(scl_drive_low, 1'b1, "read accept scl low");
+        expect(sda_drive_low, 1'b0, "read accept sda release");
+
+        tick();
+        tick();
+        sda_i = 1'b1;
+        tick();
+        expect(bit_out, 1'b1, "read samples high");
+        expect(cmd_ack, 1'b0, "read sample no ack");
+
+        tick();
+        expect(cmd_ack, 1'b1, "read ack after sample");
+        expect(scl_drive_low, 1'b1, "read finish pulls scl low");
+
+        cmd = 2'd1;
+        cmd_valid = 1'b1;
+        tick();
+        cmd_valid = 1'b0;
+        expect(scl_drive_low, 1'b1, "stop accept scl low");
+        expect(sda_drive_low, 1'b1, "stop accept sda low");
+        expect(busy, 1'b1, "stop accept still busy");
+
+        tick();
+        expect(scl_drive_low, 1'b1, "stop setup scl low");
+        expect(sda_drive_low, 1'b1, "stop setup sda low");
+
+        tick();
+        expect(scl_drive_low, 1'b0, "stop releases scl");
+        expect(sda_drive_low, 1'b1, "stop keeps sda low");
+
+        tick();
+        expect(cmd_ack, 1'b0, "stop high observe no ack");
+        expect(busy, 1'b1, "stop high observe still busy");
+
+        tick();
+        expect(cmd_ack, 1'b1, "stop ack");
+        expect(busy, 1'b0, "stop clears busy");
+        expect(scl_drive_low, 1'b0, "stop releases scl final");
+        expect(sda_drive_low, 1'b0, "stop releases sda final");
+
+        $display("PASS");
+        $finish;
+    end
+endmodule
*** End Patch


Exit code: 0
Wall time: 0 seconds
Output:
Success. Updated the following files:
A /tmp/tb_dut.sv
The temporary testbench is ready. I’m compiling and running it now; it checks that observed `scl_i` highs do not collapse the next visible phase into the same clock edge.
shell
iverilog -g2012 -Wall -o /tmp/tb_dut.vvp /app/dut.sv /tmp/tb_dut.sv && vvp /tmp/tb_dut.vvp
output
Chunk ID: 07e113
Wall time: 0.0000 seconds
Process exited with code 126
Original token count: 1324
Output:
/tmp/tb_dut.sv:45: syntax error
/tmp/tb_dut.sv:45: error: Invalid module item.
/tmp/tb_dut.sv:49: syntax error
/tmp/tb_dut.sv:51: error: Invalid module item.
/tmp/tb_dut.sv:53: syntax error
/tmp/tb_dut.sv:58: error: Invalid module item.
/tmp/tb_dut.sv:59: syntax error
/tmp/tb_dut.sv:59: error: Invalid module instantiation
/tmp/tb_dut.sv:60: error: Invalid module instantiation
/tmp/tb_dut.sv:61: error: Invalid module instantiation
/tmp/tb_dut.sv:62: error: Invalid module instantiation
/tmp/tb_dut.sv:63: error: Invalid module instantiation
/tmp/tb_dut.sv:66: syntax error
/tmp/tb_dut.sv:66: error: Invalid module instantiation
/tmp/tb_dut.sv:69: syntax error
/tmp/tb_dut.sv:69: error: Invalid module instantiation
/tmp/tb_dut.sv:70: error: Invalid module instantiation
/tmp/tb_dut.sv:72: syntax error
/tmp/tb_dut.sv:72: error: Invalid module instantiation
/tmp/tb_dut.sv:73: error: Invalid module item.
/tmp/tb_dut.sv:74: syntax error
/tmp/tb_dut.sv:74: error: Invalid module item.
/tmp/tb_dut.sv:75: syntax error
/tmp/tb_dut.sv:75: error: Invalid module item.
/tmp/tb_dut.sv:76: syntax error
/tmp/tb_dut.sv:76: error: Invalid module item.
/tmp/tb_dut.sv:79: syntax error
/tmp/tb_dut.sv:79: error: Invalid module item.
/tmp/tb_dut.sv:80: syntax error
/tmp/tb_dut.sv:80: error: Invalid module item.
/tmp/tb_dut.sv:81: syntax error
/tmp/tb_dut.sv:81: error: Invalid module item.
/tmp/tb_dut.sv:84: syntax error
/tmp/tb_dut.sv:84: error: Invalid module item.
/tmp/tb_dut.sv:85: syntax error
/tmp/tb_dut.sv:85: error: Invalid module item.
/tmp/tb_dut.sv:86: syntax error
/tmp/tb_dut.sv:86: error: Invalid module item.
/tmp/tb_dut.sv:89: syntax error
/tmp/tb_dut.sv:89: error: Invalid module item.
/tmp/tb_dut.sv:90: syntax error
/tmp/tb_dut.sv:90: error: Invalid module item.
/tmp/tb_dut.sv:91: syntax error
/tmp/tb_dut.sv:91: error: Invalid module item.
/tmp/tb_dut.sv:93: syntax error
/tmp/tb_dut.sv:93: error: Invalid module instantiation
/tmp/tb_dut.sv:94: error: Invalid module instantiation
/tmp/tb_dut.sv:95: error: Invalid module instantiation
/tmp/tb_dut.sv:97: syntax error
/tmp/tb_dut.sv:97: error: Invalid module instantiation
/tmp/tb_dut.sv:98: error: Invalid module item.
/tmp/tb_dut.sv:99: syntax error
/tmp/tb_dut.sv:99: error: Invalid module item.
/tmp/tb_dut.sv:100: syntax error
/tmp/tb_dut.sv:100: error: Invalid module item.
/tmp/tb_dut.sv:103: syntax error
/tmp/tb_dut.sv:103: error: Invalid module item.
/tmp/tb_dut.sv:104: syntax error
/tmp/tb_dut.sv:104: error: Invalid module item.
/tmp/tb_dut.sv:107: syntax error
/tmp/tb_dut.sv:107: error: Invalid module item.
/tmp/tb_dut.sv:108: syntax error
/tmp/tb_dut.sv:108: error: Invalid module item.
/tmp/tb_dut.sv:109: syntax error
/tmp/tb_dut.sv:109: error: Invalid module item.
/tmp/tb_dut.sv:111: syntax error
/tmp/tb_dut.sv:111: error: Invalid module instantiation
/tmp/tb_dut.sv:113: syntax error
/tmp/tb_dut.sv:113: error: Invalid module item.
/tmp/tb_dut.sv:114: syntax error
/tmp/tb_dut.sv:114: error: Invalid module item.
/tmp/tb_dut.sv:117: syntax error
/tmp/tb_dut.sv:117: error: Invalid module item.
/tmp/tb_dut.sv:118: syntax error
/tmp/tb_dut.sv:118: error: Invalid module item.
/tmp/tb_dut.sv:120: syntax error
/tmp/tb_dut.sv:120: error: Invalid module instantiation
/tmp/tb_dut.sv:121: error: Invalid module instantiation
/tmp/tb_dut.sv:122: error: Invalid module instantiation
/tmp/tb_dut.sv:124: syntax error
/tmp/tb_dut.sv:124: error: Invalid module instantiation
/tmp/tb_dut.sv:125: error: Invalid module item.
/tmp/tb_dut.sv:126: syntax error
/tmp/tb_dut.sv:126: error: Invalid module item.
/tmp/tb_dut.sv:130: syntax error
/tmp/tb_dut.sv:130: error: Invalid module instantiation
/tmp/tb_dut.sv:132: syntax error
/tmp/tb_dut.sv:132: error: Invalid module item.
/tmp/tb_dut.sv:133: syntax error
/tmp/tb_dut.sv:133: error: Invalid module item.
/tmp/tb_dut.sv:136: syntax error
/tmp/tb_dut.sv:136: error: Invalid module item.
/tmp/tb_dut.sv:137: syntax error
/tmp/tb_dut.sv:137: error: Invalid module item.
/tmp/tb_dut.sv:139: syntax error
/tmp/tb_dut.sv:139: error: Invalid module instantiation
/tmp/tb_dut.sv:140: error: Invalid module instantiation
/tmp/tb_dut.sv:142: syntax error
/tmp/tb_dut.sv:142: error: Invalid module instantiation
/tmp/tb_dut.sv:143: error: Invalid module item.
/tmp/tb_dut.sv:144: syntax error
/tmp/tb_dut.sv:144: error: Invalid module item.
/tmp/tb_dut.sv:145: syntax error
/tmp/tb_dut.sv:145: error: Invalid module item.
/tmp/tb_dut.sv:148: syntax error
/tmp/tb_dut.sv:148: error: Invalid module item.
/tmp/tb_dut.sv:149: syntax error
/tmp/tb_dut.sv:149: error: Invalid module item.
/tmp/tb_dut.sv:152: syntax error
/tmp/tb_dut.sv:152: error: Invalid module item.
/tmp/tb_dut.sv:153: syntax error
/tmp/tb_dut.sv:153: error: Invalid module item.
/tmp/tb_dut.sv:156: syntax error
/tmp/tb_dut.sv:156: error: Invalid module item.
/tmp/tb_dut.sv:157: syntax error
/tmp/tb_dut.sv:157: error: Invalid module item.
/tmp/tb_dut.sv:160: syntax error
/tmp/tb_dut.sv:160: error: Invalid module item.
/tmp/tb_dut.sv:161: syntax error
/tmp/tb_dut.sv:161: error: Invalid module item.
/tmp/tb_dut.sv:162: syntax error
/tmp/tb_dut.sv:162: error: Invalid module item.
/tmp/tb_dut.sv:163: syntax error
/tmp/tb_dut.sv:163: error: Invalid module item.
/tmp/tb_dut.sv:167: syntax error
I give up.
The submitted design still compiles; the temporary bench failed because I used `expect` as a task name, which is reserved in SystemVerilog. I’m renaming that helper and rerunning.
shell
nl -ba /tmp/tb_dut.sv | sed -n '35,60p'
output
Chunk ID: 85d64a
Wall time: 0.0000 seconds
Process exited with code 0
Original token count: 180
Output:
    35	    always #5 clk = ~clk;
    36	
    37	    task tick;
    38	        begin
    39	            @(negedge clk);
    40	            @(posedge clk);
    41	            #1;
    42	        end
    43	    endtask
    44	
    45	    task expect;
    46	        input value;
    47	        input expected;
    48	        input [160*8-1:0] name;
    49	        begin
    50	            if (value !== expected) begin
    51	                $display("FAIL %0s got %0b expected %0b", name, value, expected);
    52	                $finish;
    53	            end
    54	        end
    55	    endtask
    56	
    57	    initial begin
    58	        rst = 1'b1;
    59	        cmd_valid = 1'b0;
    60	        bit_in = 1'b0;
I’ll patch only the temporary bench helper name; `/app/dut.sv` does not need a change from this compile issue.
shell
perl -0pi -e 's/task expect;/task check;/g; s/expect\(/check(/g' /tmp/tb_dut.sv
output
Chunk ID: ae0377
Wall time: 0.0000 seconds
Process exited with code 0
Original token count: 0
Output:
The temporary helper is renamed; I’m rerunning the simulation now.
shell
iverilog -g2012 -Wall -o /tmp/tb_dut.vvp /app/dut.sv /tmp/tb_dut.sv && vvp /tmp/tb_dut.vvp
output
Chunk ID: 0c7ff6
Wall time: 0.0000 seconds
Process exited with code 0
Original token count: 89
Output:
warning: Some design elements have no explicit time unit and/or
       : time precision. This may cause confusing timing results.
       : Affected design elements are:
       :   -- module I2cBitCommandEngine declared here: /app/dut.sv:35
       :   -- module TopModule declared here: /app/dut.sv:1
PASS
/tmp/tb_dut.sv:166: $finish called at 216000 (1ps)
The focused simulation passed. I’m doing one final diff review of the submitted file to make sure the public module and registered behavior match the prompt.
shell
git diff -- /app/dut.sv
output
Chunk ID: f3d8fd
Wall time: 0.0000 seconds
Process exited with code 127
Original token count: 11
Output:
/bin/bash: line 1: git: command not found
shell
nl -ba /app/dut.sv | sed -n '1,260p'
output
Chunk ID: ba15ef
Wall time: 0.0000 seconds
Process exited with code 0
Original token count: 2342
Output:
     1	module TopModule (
     2	    input clk,
     3	    input rst,
     4	    input cmd_valid,
     5	    input bit_in,
     6	    input scl_i,
     7	    input sda_i,
     8	    input [1:0] cmd,
     9	    output cmd_ack,
    10	    output busy,
    11	    output al,
    12	    output bit_out,
    13	    output scl_drive_low,
    14	    output sda_drive_low
    15	);
    16	
    17	    I2cBitCommandEngine engine (
    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 I2cBitCommandEngine (
    36	    input clk,
    37	    input rst,
    38	    input cmd_valid,
    39	    input bit_in,
    40	    input scl_i,
    41	    input sda_i,
    42	    input [1:0] cmd,
    43	    output reg cmd_ack,
    44	    output reg busy,
    45	    output reg al,
    46	    output reg bit_out,
    47	    output reg scl_drive_low,
    48	    output reg sda_drive_low
    49	);
    50	
    51	    localparam [1:0] CMD_START = 2'd0;
    52	    localparam [1:0] CMD_STOP  = 2'd1;
    53	    localparam [1:0] CMD_WRITE = 2'd2;
    54	    localparam [1:0] CMD_READ  = 2'd3;
    55	
    56	    localparam [3:0] ST_READY             = 4'd0;
    57	    localparam [3:0] ST_START_WAIT_SCL    = 4'd1;
    58	    localparam [3:0] ST_START_SDA_LOW     = 4'd2;
    59	    localparam [3:0] ST_START_FINISH      = 4'd3;
    60	    localparam [3:0] ST_STOP_SETUP        = 4'd4;
    61	    localparam [3:0] ST_STOP_RELEASE_SCL  = 4'd5;
    62	    localparam [3:0] ST_STOP_WAIT_SCL     = 4'd6;
    63	    localparam [3:0] ST_STOP_FINISH       = 4'd7;
    64	    localparam [3:0] ST_WRITE_SETUP       = 4'd8;
    65	    localparam [3:0] ST_WRITE_RELEASE_SCL = 4'd9;
    66	    localparam [3:0] ST_WRITE_WAIT_SCL    = 4'd10;
    67	    localparam [3:0] ST_WRITE_FINISH      = 4'd11;
    68	    localparam [3:0] ST_READ_SETUP        = 4'd12;
    69	    localparam [3:0] ST_READ_RELEASE_SCL  = 4'd13;
    70	    localparam [3:0] ST_READ_WAIT_SCL     = 4'd14;
    71	    localparam [3:0] ST_READ_FINISH       = 4'd15;
    72	
    73	    reg [3:0] state;
    74	    reg write_bit;
    75	
    76	    always @(posedge clk) begin
    77	        if (rst) begin
    78	            state <= ST_READY;
    79	            write_bit <= 1'b0;
    80	            cmd_ack <= 1'b0;
    81	            busy <= 1'b0;
    82	            al <= 1'b0;
    83	            bit_out <= 1'b0;
    84	            scl_drive_low <= 1'b0;
    85	            sda_drive_low <= 1'b0;
    86	        end else begin
    87	            cmd_ack <= 1'b0;
    88	
    89	            case (state)
    90	                ST_READY: begin
    91	                    if (cmd_valid) begin
    92	                        case (cmd)
    93	                            CMD_START: begin
    94	                                busy <= 1'b1;
    95	                                scl_drive_low <= 1'b0;
    96	                                sda_drive_low <= 1'b0;
    97	                                state <= ST_START_WAIT_SCL;
    98	                            end
    99	
   100	                            CMD_STOP: begin
   101	                                if (busy) begin
   102	                                    scl_drive_low <= 1'b1;
   103	                                    sda_drive_low <= 1'b1;
   104	                                    state <= ST_STOP_SETUP;
   105	                                end
   106	                            end
   107	
   108	                            CMD_WRITE: begin
   109	                                if (busy) begin
   110	                                    write_bit <= bit_in;
   111	                                    scl_drive_low <= 1'b1;
   112	                                    sda_drive_low <= ~bit_in;
   113	                                    state <= ST_WRITE_SETUP;
   114	                                end
   115	                            end
   116	
   117	                            CMD_READ: begin
   118	                                if (busy) begin
   119	                                    scl_drive_low <= 1'b1;
   120	                                    sda_drive_low <= 1'b0;
   121	                                    state <= ST_READ_SETUP;
   122	                                end
   123	                            end
   124	                        endcase
   125	                    end
   126	                end
   127	
   128	                ST_START_WAIT_SCL: begin
   129	                    scl_drive_low <= 1'b0;
   130	                    sda_drive_low <= 1'b0;
   131	                    if (scl_i) begin
   132	                        if (!sda_i) begin
   133	                            al <= 1'b1;
   134	                        end
   135	                        state <= ST_START_SDA_LOW;
   136	                    end
   137	                end
   138	
   139	                ST_START_SDA_LOW: begin
   140	                    scl_drive_low <= 1'b0;
   141	                    sda_drive_low <= 1'b1;
   142	                    state <= ST_START_FINISH;
   143	                end
   144	
   145	                ST_START_FINISH: begin
   146	                    scl_drive_low <= 1'b1;
   147	                    sda_drive_low <= 1'b1;
   148	                    cmd_ack <= 1'b1;
   149	                    state <= ST_READY;
   150	                end
   151	
   152	                ST_STOP_SETUP: begin
   153	                    scl_drive_low <= 1'b1;
   154	                    sda_drive_low <= 1'b1;
   155	                    state <= ST_STOP_RELEASE_SCL;
   156	                end
   157	
   158	                ST_STOP_RELEASE_SCL: begin
   159	                    scl_drive_low <= 1'b0;
   160	                    sda_drive_low <= 1'b1;
   161	                    state <= ST_STOP_WAIT_SCL;
   162	                end
   163	
   164	                ST_STOP_WAIT_SCL: begin
   165	                    scl_drive_low <= 1'b0;
   166	                    sda_drive_low <= 1'b1;
   167	                    if (scl_i) begin
   168	                        state <= ST_STOP_FINISH;
   169	                    end
   170	                end
   171	
   172	                ST_STOP_FINISH: begin
   173	                    scl_drive_low <= 1'b0;
   174	                    sda_drive_low <= 1'b0;
   175	                    busy <= 1'b0;
   176	                    cmd_ack <= 1'b1;
   177	                    state <= ST_READY;
   178	                end
   179	
   180	                ST_WRITE_SETUP: begin
   181	                    scl_drive_low <= 1'b1;
   182	                    sda_drive_low <= ~write_bit;
   183	                    state <= ST_WRITE_RELEASE_SCL;
   184	                end
   185	
   186	                ST_WRITE_RELEASE_SCL: begin
   187	                    scl_drive_low <= 1'b0;
   188	                    sda_drive_low <= ~write_bit;
   189	                    state <= ST_WRITE_WAIT_SCL;
   190	                end
   191	
   192	                ST_WRITE_WAIT_SCL: begin
   193	                    scl_drive_low <= 1'b0;
   194	                    sda_drive_low <= ~write_bit;
   195	                    if (scl_i) begin
   196	                        if (write_bit && !sda_i) begin
   197	                            al <= 1'b1;
   198	                        end
   199	                        state <= ST_WRITE_FINISH;
   200	                    end
   201	                end
   202	
   203	                ST_WRITE_FINISH: begin
   204	                    scl_drive_low <= 1'b1;
   205	                    sda_drive_low <= ~write_bit;
   206	                    cmd_ack <= 1'b1;
   207	                    state <= ST_READY;
   208	                end
   209	
   210	                ST_READ_SETUP: begin
   211	                    scl_drive_low <= 1'b1;
   212	                    sda_drive_low <= 1'b0;
   213	                    state <= ST_READ_RELEASE_SCL;
   214	                end
   215	
   216	                ST_READ_RELEASE_SCL: begin
   217	                    scl_drive_low <= 1'b0;
   218	                    sda_drive_low <= 1'b0;
   219	                    state <= ST_READ_WAIT_SCL;
   220	                end
   221	
   222	                ST_READ_WAIT_SCL: begin
   223	                    scl_drive_low <= 1'b0;
   224	                    sda_drive_low <= 1'b0;
   225	                    if (scl_i) begin
   226	                        bit_out <= sda_i;
   227	                        state <= ST_READ_FINISH;
   228	                    end
   229	                end
   230	
   231	                ST_READ_FINISH: begin
   232	                    scl_drive_low <= 1'b1;
   233	                    sda_drive_low <= 1'b0;
   234	                    cmd_ack <= 1'b1;
   235	                    state <= ST_READY;
   236	                end
   237	
   238	                default: begin
   239	                    state <= ST_READY;
   240	                end
   241	            endcase
   242	        end
   243	    end
   244	
   245	endmodule
Implemented [dut.sv](/app/dut.sv) with: - `TopModule` using the requested port list. - Instantiated `I2cBitCommandEngine`. - Fully registered outputs with synchronous active-high reset. - Explicit command phases for start, stop, write, and read timing. - Sticky `al` behavior for start/write-1 high-SCL arbitration loss. Verification: - `iverilog -g2012 -Wall -tnull /app/dut.sv` passes. - A focused temporary simulation for start/write/read/stop phase timing also 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=0 busy=0 al=0 bit_out=0 scl=0 sda=0
__CHIPBENCH_MISMATCH_SUMMARY__: mismatches=0 samples=2351

Reproduce this trial: git checkout 2f94510 && PYTHONPATH=src python3 scripts/build_site.py , then open trial/trial_79c95e0c5c1b4199. Re-running the agent live requires EVAL_PLATFORM_ENABLE_OAUTH_SMOKE=1 and is non-deterministic.

Trial trial_79c95e0c5c1b4199 · verifier authoritative; classifier explanatory.