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Medical Laser Controller — Bit-Level SPI Verification and Fault Injection

The laser driver emulated as the counterpart, the SPI verified down to the bit, and safety-relevant faults injected deliberately — without a real laser system.

Industry: Manufacturer of medical laser systems (laser lithotripsy).

The challenge

A dual-core safety controller (Arm Cortex-M7 + Cortex-M4) drives the laser pump diodes, shutter, optical bench and a multi-stage safety chain. The firmware and the interfaces to the laser driver must be fully validated, including the fault cases.

  • Faults on the SPI to the laser driver or in the interlock logic are not acceptable in the field.
  • Development and test should be possible without a real laser system and without a patient.
  • The safety chain is verified reproducibly not only in the good case, but also under fault conditions.

The LoopCheck solution

A counterpart adapted to the controller reproduces its environment at the development desk. The customer MCU is connected through its real interfaces, the SPI is verified bit-exact, and faults are injected in a targeted way.

A LoopCheck test bench: the controller connected to its emulated environment

  • Laser driver emulated — serial links, trigger in/out and interlock/enable, with a power-off fail-safe.
  • High-speed SPI verified at the bit level; analog setpoints (pilot and laser power) reproduced via digital potentiometers.
  • Full safety chain — foot pedal, start button, laser stop, door interlock, blast shield and fiber detection.
  • Firmware of both cores flashed automatically.

Targeted fault injection

Faults that would be safety-relevant in the field are produced reproducibly on the bench, without a real laser system:

  • SPI bit errors and corrupted frames toward the laser driver
  • Interlock and enable signals opened deliberately (door, laser stop, foot switch), even during an active trigger — the power-off fail-safe is verified
  • Trigger-timing errors and setpoint manipulation via the digital potentiometers

Result

  • Bit level

    SPI to the laser driver verified bit-exact.

  • No laser system

    Development and test without a real laser system.

  • Fault cases

    Safety chain verified under fault conditions too.

Related: Safety-critical systems · Cyber Resilience Act · All reference projects