sim_fetch.py¶

Extract a file from a running native_sim Zephyr instance.

Background¶

The Zephyr FUSE bridge (CONFIG_FUSE_FS_ACCESS) mounts the simulator’s filesystem on the host, but opens files write-only, so cp from the FUSE mount fails with EIO. sim_fetch.py works around this by dumping the file over the shell console using fs read <path> and reconstructing the bytes from the hex dump on the host.

The hex dump format emitted by subsys/fs/shell.c cmd_read is:

File size: <n>
<8 hex digits offset>  <up to 16 "NN " bytes>   <ascii gutter>
...

Modes¶

The script exposes two subcommands:

Mode	Description
`parse`	Parse a previously captured console log and write the bytes of one `fs read` invocation to disk.
`pexpect`	Spawn a `native_sim` binary, drive the shell, and fetch one or more files in a single step. Requires the `pexpect` Python package.

`parse`¶

python3 tools/sim_fetch.py parse -o OUTPUT [-i INPUT] [--expect-size N]

-i / --input — path to captured console log (- for stdin, default).
-o / --output — destination file on the host.
--expect-size — fail unless the dump header reports this size.

The last complete dump in the input is chosen; partial or interrupted dumps are skipped.

`pexpect`¶

python3 tools/sim_fetch.py pexpect <zephyr.exe> \
    --fetch REMOTE LOCAL [--fetch REMOTE LOCAL ...] \
    [--await-ready PATTERN] [--pre-command CMD] [--wait-for PATTERN] \
    [--prompt PROMPT] [--timeout S] [--await-timeout S] \
    [--wait-timeout S] [--fetch-timeout S] [-v]

Key options:

--fetch REMOTE LOCAL — repeatable; REMOTE is the Zephyr path (e.g. /RAM:/data/flight_0.influx), LOCAL is the host destination.
--await-ready PATTERN — block until this regex is seen after boot before sending any --pre-command. Useful for asynchronous startup such as attitude calibration.
--pre-command CMD — shell command(s) to send before fetching (repeatable).
--wait-for PATTERN — after each --pre-command, wait for this regex instead of the shell prompt (e.g. for a simulator that keeps streaming).
The --*-timeout options control each phase independently.

After all fetches the script issues kernel reboot cold and closes the child.

Example¶

After building the sensor board for the simulator (west build -p -b native_sim sensor_board):

python3 ./tools/sim_fetch.py pexpect \
    build/zephyr/zephyr.exe \
    --await-ready "Attitude calibrated" \
    --pre-command "sim launch" \
    --wait-for "LANDED" \
    --wait-timeout 600 \
    --fetch /RAM:/data/flight_0.influx flight_logs/sim_fetch/flights.influx \
    --fetch /RAM:/state/audit.0       flight_logs/sim_fetch/state_audit \
    -v

Requirements¶

Python 3.10+
pexpect (only for the pexpect mode): pip install pexpect