How to use
- Copy the installation command and review the source package before installing it in your own agent environment.
- Check the source document for required tools, credentials and supported hosts.
- Describe your input and desired deliverable; review the output against the source material.
npx skills add https://github.com/mohitmishra786/low-level-dev-skills --skill protocol-analysisBefore you start
- Installation does not include a model subscription, API allowance or permission to access your files.
- Repository stars and installation counts describe activity, not an independent quality or security test.
Original skill document
Rendered from the source repository. Headings, examples, code, tables, links, and referenced images are preserved.
Protocol Analysis (I2C / SPI / UART)
Purpose
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.
When to Use
- 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)
Workflow
1. Capture stack
Physical probe → logic analyzer hardware (or GPIO bit-bang)
├── sigrok-cli / PulseView GUI
├── Protocol decoder (i2c, spi, uart)
└── Export VCD/CSV for scriptsOpen-source: sigrok with cheap FX2LA boards.
2. PulseView quick start
bash
# List devices
pulseview
# CLI capture (device-dependent)
sigrok-cli --driver fx2lafw --config samplerate=1MHz \
--channels 0=SDA,1=SCL \
--samples 1m \
--protocols i2c3. I2C decode expectations
| 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.
4. SPI decode
Check mode (CPOL/CPHA), bit order (MSB first typical), CS polarity, and word size. Compare to spi_setup() in skills/kernel-dev/bus-drivers-i2c-spi.
5. UART decode
Set baud (9600/115200), frame (8N1), and signal polarity. Async — sample rate must be ≥ 4× baud for LA.
6. Python post-process (csv)
python
import csv
with open("capture.csv") as f:
for ts, ch0, ch1 in csv.reader(f):
# edge detect, reconstruct bits
pass7. Correlate with firmware
Logic capture timestamp
├── Match driver reg write sequence
├── Compare inter-byte delay vs datasheet max
└── Flag extra clock pulses (mode fault)8. Agent usage
/protocol-analysis Decode this I2C capture — device NACKs after register 0x0F writeCommon Problems
| Symptom | Cause | Fix |
|---|---|---|
| Garbage decode | Wrong samplerate | ≥ 4× bus speed |
| Floating lines | Missing pull-ups | Enable internal pull or external |
| SPI shifted bits | Mode mismatch | CPOL/CPHA table from RM |
| UART framing errors | Baud drift | Measure actual bit time |
| No decoder | Missing sigrok build | Install sigrok-cli + decoders |
Related Skills
skills/baremetal/spi-i2c-baremetal— firmware-side protocolskills/baremetal/uart-serial-baremetal— UART configskills/kernel-dev/bus-drivers-i2c-spi— kernel transactionsskills/profilers/strace-ltrace— userspace syscall trace analogskills/embedded/openocd-jtag— scope alongside SWD debug
