openm454

An open driver, command-line interface and MCP server for the DreamSourceLab DSCope M454 USB mixed-signal oscilloscope (4 analog channels up to 400 MSa/s, 8 digital channels, built-in 0-3 V signal generator), written so that an AI agent (Claude Code, or any MCP client) can capture and analyze real signals by itself, without the vendor GUI.

The M454 speaks a newer ("v3") USB protocol than the devices supported by the open-source DSView. The protocol was recovered from DSWave 1.2.1 by static analysis, by driving DSWave's own hardware layer through injected commands and by USB tracing; see docs/PROTOCOL.md.

Use

Requirements: Windows, Python 3.10+, the scope bound to WinUSB (it is by default), and DSWave 1.2.1, needed once to extract the FPGA bitstream (it is never redistributed). Close DSWave before using the driver: the scope accepts one USB client.

pip install openm454            # or, from a clone: pip install -e .

Point OPENM454_DSWAVE at DSWave's DSWave.exe (or its folder), or copy the DSWave folder to DSWave/ in the openm454 folder: the clone itself, or for an installed copy %LOCALAPPDATA%\openm454 (~/.local/share/openm454 elsewhere; OPENM454_HOME overrides it). That folder also holds the cached bitstream (firmware/), state (state/) and captures (captures/).

python -m openm454 info
python -m openm454 capture -c A1,D0 --vdiv 1V --offset 1.5V --timebase 200us --trig A1:rise:1.4V
python -m openm454 watch -c A1 --every 0.5s --count 10 --fields A1.freq_hz,A1.vpp_v
python -m openm454 awg set --wave sine --freq 10k --low 0V --high 2V
python -m openm454 analyze captures/<file>.npz --window -1ms:1ms
python -m openm454 capture -c D0,D1 --rate 20M --duration 2ms --trig D0:pulse>:200us --decode "i2c:scl=D0,sda=D1"
python -m openm454 selftest

Recording modes and measured speeds

Measured on the M454 over USB 3 with every input on a 1 kHz square, every period checked for gaps (2026-11-01/02):

• The data rate is rate x (analog channels + digital channels / 8) bytes/s.
• stream: real time at DSWave's 100 MB/s ceiling and at 200 MB/s. At 400 MB/s the readout ran at 270-290 MB/s and the rest waited in the sample memory; the record arrived complete. 12 channels at 50 MSa/s (250 MB/s, ~2 s records): 0.74 / 0.66 s between records when sent while acquired (the default), 2.35 / 2.45 s with --record-first; records complete and continuous.
• log: 150 MB/s (2 analog + 8 digital at 50 MSa/s) for 3 min (27 GB) and for 30 s to disk with a constant host lag; 200 MB/s (2 analog at 100 MSa/s) for 20 s without backlog; 5 MB/s for 10 min. At 250 MB/s (4 analog + 8 digital at 50 MSa/s) the readout reached ~200 MB/s and the backlog grew ~55 MB/s. A 300 MB/s burst of 3 s (2 analog + 8 digital at 100 MSa/s) read out at 266 MB/s and stayed complete.
• log above 100 MSa/s interleaves the converters exactly as capture does (DSWave never does this in loop mode). Verified on the scope: 1 analog channel at 200 and 400 MSa/s, 2 analog at 200, 2 digital at 400, 4 digital at 200 and mixed sets. 2 digital channels at 400 MSa/s or 4 at 200 MSa/s are 100 MB/s and run without a time limit. 1 analog channel at 200 MSa/s (200 MB/s) ran 10 s without backlog.
• The sample memory is a 512 MiB ring in loop mode: the host may fall up to ~512 MiB behind without losing data (host stalls of 10 s at 50 MB/s were absorbed). Beyond that the scope overwrites unread data without any flag and keeps streaming: from then on the data are garbage (one phase step on analog, the digital channels misaligned) until the run is restarted. Measured with the driver's backlog estimate, the break came at 508-514 MiB (three runs), so log stops at 480 MiB.
• log --plan (no device needed) prints the verdict for a rate, the gap-free limit and recommendation (next section), how long the run can last (max_duration_s) and where the data goes: RAM by default (refused when it does not fit the budget unless --keep-last), --storage disk for ~256 MB chunk files (it warns about SSD wear: 200 MB/s is 720 GB per hour), --storage none for statistics only.
• bench measures this PC (free RAM, decode speed, disk write speed, USB readout) and records how much RAM and disk the owner allows for recordings and the data folder (bench --ram 8GB --disk 50GB --dir <folder>, state/host.json); log takes its defaults from there. Measured here: decode 468 MB/s, USB readout 206 MB/s (4 analog + 8 digital) / 267 MB/s (2 analog + 8 digital).

Above the readout limit: how log decides

D = the data rate; R = how fast this PC reads the scope while it acquires. R depends on the channel set (measured here: 202 MB/s for 4 analog + 8 digital at 50 MSa/s, 264 MB/s for the same at 100 MSa/s and for 2 analog + 8 digital at 100 MSa/s, 275 MB/s for 4 analog at 100 MSa/s).

1. R is measured, not assumed: the first log above 150 MB/s with a channel set runs a probe of up to 2 s (a probe line) and remembers R in state/host.json: the measured rate, or "kept up" (R >= D) when it reads at

   = 99 % of D. Later runs above 150 MB/s refresh it when the result is clear (still falling behind at a steady rate at the stop, or caught up at the end), and so do bench and --remeasure. Until then --plan assumes 190 MB/s and marks the plan provisional.

2. D <= R: the host keeps up (sustained / near_limit); the run lasts as long as the storage allows.
3. D > R: the scope gets D - R ahead per second (backlog_growth_mb_s), and it sends nothing after a stop, so the unread part is lost. A log is gap-free for at most gapfree_max_s = 480 MiB x R / (D x (D - R)), the signal the host has read when the scope is 480 MiB ahead. A shorter log runs normally.
4. A longer log (or forever) is compared with what stream would do with the same channels and settings (stream_alternative, from stream's own planning): records of up to 400M samples per channel / 512 MiB, sent while acquired, with gaps of record x (D - R) / R + 0.18 s, at stream's rates (1-2-5 steps x interleave; it may run a domain slower, e.g. 2 analog + 8 digital at 100 MSa/s samples the digital channels at 50 MSa/s):
   • STREAM_BETTER (exit 2): stream samples every channel at least as fast, and its records are at least as long as the log's one gap-free piece (or one record holds the whole duration). The error carries the stream command, with the same vertical settings.
   • NEEDS_FORCE (exit 2): the log's piece is the longest gap-free recording possible but shorter than asked. --force records it and then stops (stop_reason ring_full, ok, with a warning); the rest of the requested time is not recorded. Both errors carry the numbers in error.plan.
5. While running, every statistics line has backlog_mb; while the backlog grows, also backlog_growth_mb_s, ring_full_in_s and gapfree_projected_s. The result has unread_at_stop_mb (acquired, never read).

Examples here: 12 channels at 50 MSa/s (250 MB/s, R = 204): gap-free 8.88 s vs stream records of 2.03 s with 0.64 s gaps, so NEEDS_FORCE; forced, the run stopped after 8.84 s (8.30 s with R = 202 in an earlier run), every period present up to the last sample. 12 channels at 100 MSa/s (500 MB/s, R = 264): 1.13 s vs 1.02 s records with 1.09 s gaps, still NEEDS_FORCE; with a readout below ~250 MB/s stream would win. 200 MB/s read at 190 MB/s: 10 MB/s backlog growth, the guard after ~50 s, 47.8 s of gap-free signal.

The backlog is estimated as D x (time since the head) - bytes received, checked on every USB transfer, against a baseline that follows the scope / PC clock difference: it may rise by at most 200 ppm x D per second, and only while the host is caught up (estimate below 16 MiB), so the estimate stays exact over hours and a real backlog is never absorbed. A guard stop while nothing arrives at all is reported as a stalled scope (TIMEOUT_DATA); a forced log that was planned to end at the guard reports ring_full, any other guard stop HOST_TOO_SLOW.

log or stream?

Both record untriggered, but they are not the same mode of the scope. log is one endless run (loop mode); stream is a series of records, each programmed with a fixed length that the scope stops at.

The restart (~0.18 s) is the same for both; the difference is what has to be read out before it. Use log for continuous recording; stream for different analog and digital rates, decoding the record, or above the readout limit when log says STREAM_BETTER or the whole time matters more than one long gap-free piece.

python -m openm454 bench --ram 8GB --disk 50GB --dir logs
python -m openm454 log --plan -c A0,D0-D7 --rate 1M --duration 10min
python -m openm454 log -c A0,D0-D7 --rate 1M --duration 10min                   # kept in RAM, one .npz at the end
python -m openm454 log -c A0,D0-D7 --rate 1M --duration forever                 # RAM ring; end it with: python -m openm454 stop
python -m openm454 stream -c D0-D7 --rate 100M --duration 60s --every 1s

Every command prints one JSON document (watch, stream and log: one per line, then the result), whether or not --json is given: measurements, applied settings, file paths. Samples are never printed (unless --dump N asks for a decimated series); captures are saved as .npz (raw codes + scaling) and .png. python -m openm454 <command> --help lists every option. Python API: openm454.scope.Scope, openm454.capture.load_capture, Capture.decode().

Protocol decoders (--decode SPEC, repeatable, on capture, watch, stream and analyze): uart:rx=D4,baud=115200|auto,bits=8,parity=none,stop=1,invert=0, spi:clk=..,mosi=..,miso=..,cs=..,mode=0..3, i2c:scl=..,sda=.., can:rx=..,bitrate=500k|auto,invert=0. They report every frame with trigger-relative times and its errors (parity/framing, partial words, NACKs, CRC/stuff/form errors), and remove the comparator chatter of slow edges. Output format: docs/schemas/decode.json. Decoding needs about 10 samples per bit or clock (I2C: 9 per SCL period, no errors; 5-6 per period still decode with well under 1 % errors). They have been checked against real buses (SPI up to 18 MHz, RS232, CAN up to 1 Mbit/s, I2C up to 400 kHz) generated by a microcontroller, including deep captures and decoded streams.

MCP server

openm454-mcp (or python -m openm454.mcp_server) serves the scope over the Model Context Protocol (stdio, no extra dependencies):

claude mcp add openm454 -- openm454-mcp

Other clients: {"mcpServers": {"openm454": {"command": "openm454-mcp"}}}. Each tool call runs one CLI command in a child process, so the scope is opened and released per call, a hang never blocks the server, and every rule of the CLI applies.

Results are summaries (detail: "full" returns the CLI's whole document); the samples stay in the .npz. Every call has a hard time limit (max_wall_s, default 180 s).

Errors

Every error has a code, a message and a hint, so the next step is clear:

Layout

• openm454/ driver: USB transport with a safety whitelist, device bring-up (FPGA, security handshake, calibration), register compiler (mso.py, reproduces DSWave's register programs exactly), stream decoder (packet.py), acquisition engine, loop-mode logger (logger.py), measurements, plots, AWG, CLI, self-test, protocol decoders (decode.py), synthetic bus traffic for tests (protosim.py) and the MCP server (mcp_server.py).
• tests/ offline tests: golden register and AWG programs, the stream decoder, the acquisition engine against a simulated device, measurements, protocol decoders on synthetic traffic, the MCP server, safety rules (python -m pytest tests).
• docs/PROTOCOL.md the recovered USB protocol.
• .github/workflows/: CI (the offline tests on Windows and Linux with OPENM454_NO_USB=1, which makes the driver refuse to open USB, and a package build) on every push; a tag vX.Y.Z equal to openm454.__version__ tests, builds and publishes to PyPI (trusted publishing) and creates a GitHub release.

What is NOT here

The vendor application, its embedded FPGA bitstream and firmware images, decompiled vendor code, raw USB traces (they contain the device's security key), the reverse-engineering workspace and the vendor datasheet are kept out of this repository.

Safety

The driver never sends the firmware-upgrade request (bRequest 0xB3), never writes the device EEPROM, and configures the FPGA only when the device reports it unconfigured.

License

GPL-3.0 (see LICENSE). DSView (GPLv3) by DreamSourceLab was used as a protocol reference. DSWave and DSCope are trademarks of DreamSourceLab; this project is not affiliated with DreamSourceLab.