Senior Firmware Engineer

SUMMARY: Design, develop, and maintain firmware for LoRaWAN module product lines (including xDot) and custom sensor applications. Work across Arm Mbed OS and Zephyr RTOS targeting STM32 and low-power Arm Cortex-M microcontrollers, delivering production AT command firmware, LoRaWAN Class A/B/C protocol compliance, and customer sensor solutions. This is the RTOS/RF-focused role required to continue LoRaWAN xDot development.

ESSENTIAL DUTIES AND RESPONSIBILITIES:

• Develop and maintain LoRaWAN module AT command firmware across multiple hardware variants
• Own the LoRaWAN MAC layer library — Class A/B/C operation, multicast, FOTA, ADR, regional parameter compliance
• Implement and validate LoRaWAN specification compliance including Class B beacon timing, ping-slot scheduling, and multicast
• Port and maintain Zephyr RTOS board support packages including board definitions, device drivers, and subsystem integration
• Develop custom LoRaWAN sensor applications using Mbed OS and Zephyr RTOS for customer-specific deployments
• Bring up and validate new hardware variants and component changes across the product line
• Design and execute comprehensive host-based test suites using CppUTest and Zephyr Twister
• Maintain bootloaders and FOTA update infrastructure for secure field updates
• Optimize power consumption for battery-operated devices targeting ultra-low-power sleep modes
• Support LoRa Alliance technical working group contributions (L2 protocol, payload schema)

QUALIFICATION REQUIREMENTS:

• 5+ years bare-metal and RTOS firmware development on Arm Cortex-M (M0+, M3, M4)
• Strong C/C++ for resource-constrained MCUs (32KB RAM / 256KB Flash targets)
• LoRaWAN protocol stack implementation experience (MAC layer, Class A/B/C, regional parameters)
• STM32 family (STM32L151, STM32L4, STM32U3) — peripherals, low-power modes, HAL/LL drivers
• Mbed OS 6.x application development and build system
• Zephyr RTOS — device tree, Kconfig, west build system, subsystem development
• SPI/I2C peripheral drivers (SX1272/SX1276/SX1262 radio, external flash, EEPROM)
• JTAG/SWD debugging, logic analyzer, RF test equipment
• Git, CI/CD (Jenkins), automated firmware testing
• AT command interface design and implementation

PHYSICAL DEMANDS:

• Lifting requirements up to 25 pounds.
• Requires sitting for periods of time and occasional standing.
• Use hands to finger, handle or feel.

WORK ENVIRONMENT:

• Working conditions are normal for an office environment. Minimal noise.
• Our Minnesota facility includes a manufacturing environment. Moderate noise level. Machinery operation requires the use of safety equipment to include but not limited to; safety glasses, hearing protection, wrist and shoe straps, and ESD smock. Loose fitting clothing and jewelry are not permitted. No food allowed in the manufacturing area. No cell phone use allowed in manufacturing area unless approved by management.

EQUIPMENT AND TOOLS USED:

• Laptop computer
• Standard office equipment