protocol-analysis

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English

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Translation

Chinese

Protocol Analysis (I2C / SPI / UART)

协议分析（I2C / SPI / UART）

Purpose

用途

Guide agents through software-side serial bus analysis: logic analyzer workflow, sigrok/PulseView decoding, correlating captures with firmware drivers, and Python-based parsing — bridging

skills/baremetal/spi-i2c-baremetal

and hardware bring-up.

指导Agent完成串行总线的软件端分析：逻辑分析仪工作流、sigrok/PulseView解码、捕获数据与固件驱动的关联，以及基于Python的解析——衔接

skills/baremetal/spi-i2c-baremetal

与硬件启动环节。

When to Use

适用场景

Sensor not responding — verify clock and data on bus
Compare kernel driver transactions vs datasheet
Document expected transaction format for CI/regression
Teaching protocol layers without expensive lab gear (sim + decode)

传感器无响应——验证总线上的时钟与数据信号
对比内核驱动事务与数据手册要求
为CI/回归测试记录预期的事务格式
在无需昂贵实验设备的情况下教授协议层知识（仿真+解码）

Workflow

工作流程

1. Capture stack

1. 捕获栈

Physical probe → logic analyzer hardware (or GPIO bit-bang)
├── sigrok-cli / PulseView GUI
├── Protocol decoder (i2c, spi, uart)
└── Export VCD/CSV for scripts

Open-source: sigrok with cheap FX2LA boards.

物理探头 → 逻辑分析仪硬件（或GPIO位 bang）
├── sigrok-cli / PulseView GUI
├── 协议解码器（i2c, spi, uart）
└── 导出VCD/CSV供脚本处理

开源方案：搭配廉价FX2LA板卡的sigrok。

2. PulseView quick start

2. PulseView快速入门

bash

undefined

bash

undefined

List devices

列出设备

pulseview

CLI capture (device-dependent)

CLI捕获（设备相关）

sigrok-cli --driver fx2lafw --config samplerate=1MHz
--channels 0=SDA,1=SCL
--samples 1m
--protocols i2c

undefined

sigrok-cli --driver fx2lafw --config samplerate=1MHz
--channels 0=SDA,1=SCL
--samples 1m
--protocols i2c

undefined

3. I2C decode expectations

3. I2C解码预期

Phase	Lines
START	SDA fall while SCL high
Address + R/W	7 bits + ACK
Data bytes	ACK per byte
STOP	SDA rise while SCL high

NACK at address → wrong

0x48

or device held in reset.

阶段	线路状态
START	SCL为高电平时SDA下降
地址 + 读/写	7位地址 + ACK
数据字节	每个字节对应一个ACK
STOP	SCL为高电平时SDA上升

地址阶段出现NACK → 地址错误（如错误的

0x48

）或设备处于复位状态。

4. SPI decode

4. SPI解码

Check mode (CPOL/CPHA), bit order (MSB first typical), CS polarity, and word size. Compare to

spi_setup()

skills/kernel-dev/bus-drivers-i2c-spi

检查模式（CPOL/CPHA）、位序（通常为MSB优先）、CS极性和字长。可与

skills/kernel-dev/bus-drivers-i2c-spi

中的

spi_setup()

进行对比。

5. UART decode

5. UART解码

Set baud (9600/115200), frame (8N1), and signal polarity. Async — sample rate must be ≥ 4× baud for LA.

设置波特率（9600/115200）、帧格式（8N1）和信号极性。异步通信——逻辑分析仪的采样率必须≥波特率的4倍。

6. Python post-process (csv)

6. Python后处理（csv格式）

python

import csv

with open("capture.csv") as f:
    for ts, ch0, ch1 in csv.reader(f):
        # edge detect, reconstruct bits
        pass