Devpsu

Agent-friendly bench power supply control, built for the Agentic Firmware Workbench. Set voltage/current, switch the output, and power-cycle the device under test on B&K Precision 1685B/1687B/1688B supplies (and Manson HCS-3xxx, which share the same protocol) — from the command line or from an AI agent via MCP.

Sibling of devpower (USB port power) and devsignal (signal generation). Typical use: an agent's DUT wedges hard enough that a debug-probe reset doesn't help — the agent runs power_cycle on the supply and the board cold-boots.

Supported hardware

Built against the 1687B (36 V / 10 A). The ASCII-over-serial protocol is shared by the 1685B (60 V / 5 A) and 1688B (18 V / 20 A) and the Manson HCS-3xxx family they're based on. USB appears as a virtual COM port (9600 8N1) — no drivers needed on macOS/Linux.

Note for the 1685B: it uses two current decimals; pass --current-decimals 2 (CLI) or current_decimals=2 (API).

Install

pip install .

Requires Python 3.10+.

Safety model

An agent controlling DUT power deserves guardrails. devpsu has four:

1. Session limits (human-in-the-loop) — on the first supply-changing MCP call of a session, the user is prompted (MCP elicitation) for the session's max voltage/current. Agent requests above them require explicit user approval; output_on/power_cycle check the present setpoints too, and output_off is never gated. Hosts without elicitation support fail safe (over-limit requests are refused).
2. Environment hard ceiling — set DEVPSU_MAX_V / DEVPSU_MAX_A and any request above them is refused before touching the hardware — not even in-session user approval overrides these.
3. The supply's own protection — devpsu limits --ovp 5.5 --ocp 1.0 programs the instrument's OVP/OCP as a second, firmware-level layer.
4. Agent-facing guidance — the MCP tool descriptions tell agents to verify setpoints against the DUT's rating before enabling the output.

Also set DEVPSU_PORT to pin the serial port on single-supply benches: auto-discovery probes USB-serial ports with a benign query, which you may not want on a bench with DUT consoles attached.

Multiple supplies

devpsu list shows every supply with its USB location, model maxima, and present setpoints. Identical supplies often ship USB bridges with the same serial number, making /dev/cu.usbserial-* names unstable - so --port (and the MCP port argument) also accepts the location string, which is tied to the physical USB topology:

$ devpsu list
/dev/cu.usbserial-0001  loc=34-2.1.4.1.2.1  max 36.2V/12.0A  set 24.0V/2.0A
/dev/cu.usbserial-4     loc=34-2.1.4.1.4    max 36.2V/12.0A  set 12.1V/3.0A
$ devpsu --port 34-2.1.4.1.4 status     # select by location

Session safety limits are kept per physical supply (keyed by location), so each rail gets its own ceiling and its own approval prompts.

CLI

devpsu list                        # probe for supplies
devpsu status                      # setpoints, live V/A, CV/CC, limits
devpsu set --volts 3.3 --amps 0.5
devpsu on / devpsu off
devpsu cycle --hold 5              # power-cycle the DUT
devpsu limits --ovp 5.5 --ocp 1.0
devpsu raw GETD                    # protocol escape hatch
devpsu --json status               # machine-readable

MCP server

devpsu-mcp runs an MCP server over stdio exposing list_supplies, get_status, set_voltage, set_current, output_on, output_off, power_cycle, and set_protection.

Register with Claude Code (with guardrails):

claude mcp add --scope user devpsu -e DEVPSU_MAX_V=5.5 -e DEVPSU_MAX_A=2 devpsu-mcp

Development

pip install -e ".[dev]"
pytest

The test suite runs against a fake serial layer — no supply required.

License

MIT