MUM Adapter Internals (Melexis Universal Master)

This document describes how the MumLinInterface adapter wraps the Melexis pymumclient and pylin packages, how frames flow across the LIN bus, and which MUM-specific behaviors callers need to understand.

Overview

Location: ecu_framework/lin/mum.py
Vendor reference scripts: vendor/automated_lin_test/ (test_led_control.py, test_auto_addressing.py, power_cycle.py)
Default MUM endpoint: 192.168.7.2 over USB-RNDIS
LIN device name on MUM: lin0
Power-control device on MUM: power_out0
Required Python packages: pylin, pymumclient (Melexis-supplied; not on PyPI). See vendor/automated_lin_test/install_packages.sh.

What the MUM gives you that BabyLIN doesn't

Built-in power control on power_out0 — the adapter calls power_up() in connect() and power_down() in disconnect(). No external Owon PSU needed for the standard flow.
Network access: the MUM is IP-reachable, so the host machine (Windows, Linux, Pi) does not need vendor native libraries — only the two Python packages.
Direct transport-layer access for sending raw frames with LIN 1.x Classic checksum (required for BSM-SNPD diagnostic frames).

What it doesn't give you

No passive listen. The MUM is master-driven. To "receive" a slave-published frame, the master sends a header on that frame ID and the slave must respond. MumLinInterface.receive(id=None) raises NotImplementedError for that reason.
No SDF / schedule manager. The adapter does not run a schedule; tests publish frames explicitly (or pull slave frames explicitly) on each call.

Mermaid: connect / receive / send

sequenceDiagram
  autonumber
  participant T as Test/Fixture
  participant A as MumLinInterface
  participant MM as pymumclient (MelexisUniversalMaster)
  participant PL as pylin (LinDevice22 / TransportLayer)
  participant E as ECU

  T->>A: connect()
  A->>MM: MelexisUniversalMaster()
  A->>MM: open_all(host)
  A->>MM: get_device(power_out0)
  A->>MM: get_device(lin0)
  A->>MM: linmaster.setup()
  A->>PL: LinBusManager(linmaster)
  A->>PL: LinDevice22(lin_bus)
  A->>PL: set baudrate
  A->>PL: get_device(bus/transport_layer)
  A->>MM: power_control.power_up()
  Note over A: sleep(boot_settle_seconds)
  A-->>T: connected

  T->>A: receive(id=0x11)
  A->>PL: send_message(master_to_slave=False, frame_id=0x11, data_length=4)
  PL->>E: header for 0x11
  E-->>PL: response bytes
  PL-->>A: bytes
  A-->>T: LinFrame(id=0x11, data=...)

  T->>A: send(LinFrame(0x0A, payload))
  A->>PL: send_message(master_to_slave=True, frame_id=0x0A, data_length=8, data=payload)
  PL->>E: header + payload (Enhanced checksum)

  T->>A: send_raw(bytes)
  A->>PL: transport_layer.ld_put_raw(data, baudrate)
  Note over PL,E: LIN 1.x Classic checksum (required for BSM-SNPD)

  T->>A: disconnect()
  A->>MM: power_control.power_down()
  A->>MM: linmaster.teardown()

Public API

MumLinInterface(host, lin_device='lin0', power_device='power_out0', baudrate=19200, frame_lengths=None, default_data_length=8, boot_settle_seconds=0.5)

LinInterface contract (matches Mock and BabyLIN adapters):

connect() — opens MUM, sets up LIN, and powers up the ECU
disconnect() — powers down and tears down (best-effort)
send(frame: LinFrame) — publishes a master-to-slave frame using Enhanced checksum
receive(id: int, timeout: float = 1.0) -> LinFrame | None — triggers a slave read for id. The timeout argument is informational; the underlying pylin call is synchronous. Any pylin exception is treated as "no data" and returns None. Passing id=None raises NotImplementedError.

MUM-only extras:

send_raw(bytes) — sends a raw LIN frame using Classic checksum via the transport layer's ld_put_raw. Use this for BSM-SNPD diagnostic frames; the firmware will reject them if Enhanced is used.
power_up() / power_down() — direct control over power_out0
power_cycle(wait=2.0) — convenience: power_down(), sleep, power_up(), then boot_settle_seconds sleep

Frame-length resolution

Because the MUM is master-driven, every receive needs to know how many bytes to ask for. The adapter resolves this from frame_lengths:

Built-in defaults for the 4SEVEN library (ALM_Status=4, ALM_Req_A=8, ConfigFrame=3, PWM_Frame=8, VF_Frame=8, Tj_Frame=8, PWM_wo_Comp=8, NVM_Debug=8).
Anything in the constructor's frame_lengths argument overrides the defaults.
If a frame ID isn't in the map, default_data_length (default 8) is used.

In YAML, hex keys work:

interface:
  type: mum
  frame_lengths:
    0x0A: 8
    0x11: 4

The config loader coerces hex strings ("0x0A") and integers alike.

Diagnostic frames (BSM-SNPD)

The vendor's test_auto_addressing.py flow runs LIN 2.1 BSM-SNPD via raw frames on 0x3C (MasterReq). The framework supports the same flow:

# inside a test that already has the MUM 'lin' fixture
data = bytearray([
    0x7F,  # NAD broadcast
    0x06,  # PCI: 6 data bytes
    0xB5,  # SID: BSM-SNPD
    0xFF,  # Supplier ID LSB
    0x7F,  # Supplier ID MSB
    0x01,  # subfunction (INIT)
    0x02,  # param 1
    0xFF,  # param 2
])
lin.send_raw(bytes(data))

send_raw() calls transport_layer.ld_put_raw(data=..., baudrate=...) which uses LIN 1.x Classic checksum. Using lin.send() for these frames would compute Enhanced checksum and the firmware would discard the frame.

Error surfaces

pymumclient is not installed / pylin is not installed — raised on connect() if the Melexis packages aren't importable. The error message points at vendor/automated_lin_test/install_packages.sh.
MUM not connected — calling send / receive / send_raw before connect() (or after disconnect()).
MUM transport layer not available — raised by send_raw when the LIN device didn't expose bus/transport_layer. Practically always available on MUM firmware that supports diagnostic frames.
pylin exceptions during receive — converted to None (treated as a timeout / no-data). Use this to drive timeout-tolerant tests without try/except in the test body.

Unit testing without hardware

The adapter accepts mum_module= and pylin_module= constructor arguments that bypass the real package imports. Tests in tests/unit/test_mum_adapter_mocked.py use simple in-memory fakes to drive the connect / send / receive / send_raw / power-cycle paths end to end. See that file for a complete shim implementation.

from ecu_framework.lin.mum import MumLinInterface

iface = MumLinInterface(
    host="10.0.0.1",
    boot_settle_seconds=0.0,
    mum_module=fake_mum,
    pylin_module=fake_pylin,
)
iface.connect()
# ... assertions ...
iface.disconnect()

Notes and pitfalls

Boot settling: After power_up() the adapter sleeps boot_settle_seconds (default 0.5 s) so the ECU has time to come up before the first frame. Increase if your ECU boots slowly.
Owon PSU coexistence: the MUM provides power on power_out0 independently of ecu_framework/power/. Leave power_supply.enabled: false for the standard MUM flow; enable it only for over/under-voltage scenarios that need a separate, programmable rail.
Networking: USB-RNDIS bring-up can take a few seconds after plugging in the MUM. If connect() fails with a connection-refused, ping 192.168.7.2 first.
Multiple MUMs: only one MUM is supported per MumLinInterface instance. Different host addresses can run different fixture sessions side-by-side.

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