| name | packet-testdata |
| description | Build systematic collection of packet logs for a GPS receiver, covering all implemented decode paths per plan/packet-testing.md |
| allowed-tools | Read, Bash, Glob, Grep, Write, Edit, AskUserQuestion, Agent, Skill |
Packet test data collection skill
Build a systematic collection of packet logs for a specific GPS receiver model, as described in plan/packet-testing.md. The goal is to produce a set of traces in gps/testdata/packets/ that exercises every implemented decode path in the receiver's lib and domain layers, and includes time messages suitable for deterministic replay testing per plan/timemsg-sync-testing.md.
This is NOT for ad-hoc packet capture during development. It is for building the curated test data collection.
Configuration approaches
There are two ways to configure GPS receivers for captures, corresponding to the two configuration modes of satpulsetool gps (see docs/man/satpulsetool-gps.1.md):
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High-level configuration uses device-independent flags like --pvt-out, --sats-out, --binary, --nmea-out, --raw-out, --time-gnss, --gnss, --survey, --reload. Currently supported on u-blox receivers (u-blox 6 through X20) and Unicore Nebulas IV (UM980, UM981, UM982, UM960). See highlevel-config.md.
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Low-level configuration uses a TOML message file (-m) containing protocol-specific commands. This works with all receivers. Message files are in per-vendor subdirectories of configs/gpsmsg/ (e.g., configs/gpsmsg/u-blox/ubx.toml, configs/gpsmsg/unicore/um980.toml, configs/gpsmsg/allystar/allystar.toml). See lowlevel-config.md.
Both approaches can be combined: use high-level config first, then a second invocation with -m to add messages that high-level config cannot reach.
Required information
- Serial device - device path (e.g.,
/dev/ttyACM0)
- Baud rate - saved baud rate in NVM
- Vendor - GPS vendor (e.g.,
u-blox, unicore)
Check CLAUDE.local.md for device and baud rate. If not found, ask the user.
Use the satpulsetool skill for reference on satpulsetool command usage.
Prerequisites
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NTP sync: The capture host must have good time sync. Verify with chronyc sources -- there should be a selected source (marked with *) and the offset should be small (under a few ms). Packet timestamps depend on wall clock accuracy.
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Stop satpulsed: The user must stop satpulsed if it is running on the device. This requires sudo. Ask the user to do this -- do not attempt it yourself.
sudo systemctl stop satpulsed
Output directory
gps/testdata/packets/<vendor>/<model>/
The model name comes from --show-receiver output (see high-level config section).
HW.toml
Create a metadata file in the output directory:
vendor = "<vendor>"
model = "<model>"
firmware = "<firmware string from --show-receiver>"
default-baud = <baud>
General principles
Read capture-principles.md for device-independent capture design principles.
Determining what to capture
Read capture-analysis.md for how to analyze the lib and domain layers to determine what messages need capturing.
Receiver-specific configuration
For receivers with high-level configuration support (u-blox, Unicore), read highlevel-config.md.
For u-blox receivers specifically, also read ubx-config.md.
For Unicore receivers (UM980, UM981, UM982), also read unicore-config.md.
For all receivers, message files in the per-vendor subdirectories of configs/gpsmsg/ provide low-level message tags. Read lowlevel-config.md for how to use these.
Capture procedure
For each capture:
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Reload (high-level config receivers only): satpulsetool gps -d <device> -s <baud> --reload to restore NVM state. This ensures no residual configuration from a prior capture leaks in. On USB, add sleep 2 after reload as the device may briefly disconnect. For receivers without high-level config, reset by power cycling or using a reset command from the message file.
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Configure (if needed): Run satpulsetool with configuration flags but without --capture or --packet-log.
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Add low-level messages (if needed): Run satpulsetool with -m <file> -t <tags> to enable messages not reachable via high-level config. This can follow a high-level config step since -m does not probe or reset the receiver.
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Capture: Run satpulsetool with --packet-log <file> --capture 30 (60 for survey). Use 30 seconds for most captures.
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Verify: Check message types in the capture with:
jq -r 'select(.out != true) | .msg' <file> | sort | uniq -c | sort -rn
Confirm steady-state messages match expectations. First-epoch residual messages from before configuration took effect are normal and expected.
After all captures
- Reload the receiver:
satpulsetool gps -d <device> -s <baud> --reload
- Ask the user to restart satpulsed.
Replay verification
After collecting all captures, build with make and run verify-replay.py (in this skill directory):
make
python3 .claude/skills/packet-testdata/verify-replay.py [--ecef x,y,z] out/amd64/satpulsetool <packet-log-directory>
If the antenna's ECEF position is known (check CLAUDE.local.md), pass it with --ecef to enable distance checks on all position events (posGeo, posECEF, survey). Without --ecef, only basic plausibility checks (valid lat/lon range, Earth-radius ECEF magnitude) are performed.
The script replays every .jsonl file through satpulsetool replay, collects all events in memory, and checks for:
- Time events have taiTime or utcTime
- TIM-TP events have ref field
- NAV-TIMEUTC events have gnss field (known to be absent for GLONASS-only configs on u-blox)
- Leap second consistency within and across files
- Per-epoch TAI agreement across post-pulse time message variants (10ms tolerance)
- Position (lat/lon and ECEF) plausibility
- Velocity plausibility for stationary receivers
- DOP values reasonable
- Survey ECEF position plausibility
- navEpoch fixLevel values valid
- Per-constellation captures: TIM-TP gnss matches expected constellation
- Cross-file: position consistency and leap second consistency
The script exits 0 if all checks pass, 1 if any problems are found. Review any findings -- some are known receiver behaviors (e.g., NAV-TIMEUTC gnss=null under GLONASS-only timing) rather than capture defects.
