Embedded C Developer

Themesoft Inc.; Englewood (CO); On-site; USD 100,000 - 140,000; Full time

Job summary

The Embedded C Developer role at Themesoft Inc. focuses on building and maintaining OpenWrt-based gateways with OpenSync, enabling LTE/5G cellular backup and multi‑WAN resiliency. You will work on OpenWrt firmware, OVSDB-based cloud configuration, and secure, scalable device management.

Ideal candidates have strong C expertise on Linux, hands-on OpenWrt/OpenSync experience, and a track record with cellular modems, WiFi drivers, and kernel debugging. Onsite Englewood, CO welcomed.

Qualifications

• 5+ years of embedded C development on Linux-based platforms.
• Experience with OpenWrt build system, UCI, and JFFS2/SquashFS overlay filesystems.
• Familiarity with OpenSync or similar cloud-managed CPE frameworks (OVSDB, protobuf, MQTT telemetry).
• Experience with cellular modem integration — AT commands, QMI, network interface management (rmnet/wwan).
• Strong understanding of Linux networking — routing, IPv4/IPv6, DHCPv4/DHCPv6, and related protocols.
• TLS mutual authentication, X.509 certificates, and secure provisioning concepts.
• Knowledge of security and tunneling protocols — IPsec, GRE, VPN overlays.

Responsibilities

• Cellular failover and multi-WAN state machines with sub-second transitions.
• LED indication logic for device status across WAN scenarios.
• Modem health monitoring and subsystem restart/recovery.
• Cloud-managed device configuration and telemetry reporting via MQTT.
• Secure cloud connectivity using mTLS and certificate-based authentication.
• Factory reset, firmware upgrade, and persistent storage management.
• IPv4/IPv6 dual-stack routing and WAN failover across interfaces.
• WiFi radio configuration and performance optimization across supported chips.

Skills

Embedded C

Linux

OpenWrt/OpenSync

LTE/5G cellular

Networking

GitLab

WiFi drivers

Kernel debugging

Cross-compilation

TLS security

Tools

OpenWrt build system

GDB

tcpdump

Make

Job description

Embedded C Developer – OpenSync/OpenWrt WiFi Router with Cellular Backup

Location: Onsite. Englewood, CO

JD:

We're looking for an Embedded C Developer to work on next-generation residential gateway platforms that combine DOCSIS/fiber WAN connectivity with LTE/5G cellular backup. You'll be developing and maintaining firmware on OpenWrt-based hardware running the OpenSync framework, with direct impact on millions of deployed customer premises equipment (CPE).

Responsibilities

• Design, develop, and debug embedded C software for Linux-based residential gateway platforms (ARM/MIPS SoC)
• Develop and maintain OpenSync managers — event-driven daemons that interact with OVSDB for cloud-managed configuration and state reporting
• Implement and optimize LTE/5G cellular failover and fallback logic including modem management, route arbitration, and WAN healthchecks
• Develop LED state machine logic to provide accurate device status indication across complex multi-WAN scenarios
• Interface with cellular modems via AT commands, QMI/MBIM, USB, and PCIe (MHI) protocols
• Work with WiFi drivers (Qualcomm/Broadcom/Atheros) for 2.4GHz, 5GHz, and 6GHz radio configuration
• Debug kernel-level issues including PCIe enumeration, USB device management, network driver crashes, and kernel panics
• Implement and maintain secure communication channels using TLS with mutual authentication and tunneling protocols
• Analyze and resolve field issues using device logs, crash dumps, and remote diagnostics
• Develop init scripts, UCI configuration handlers, and persistent storage management for OpenWrt
• Write unit tests and participate in code reviews via GitLab merge requests
• Collaborate with hardware teams, QA, cloud platform engineers, and service provider partners

Required Skills

• 5+ years of embedded C development on Linux-based platforms
• Strong proficiency in C programming — pointers, memory management, IPC, event-driven architectures
• Experience with OpenWrt build system, package management, UCI configuration, and JFFS2/SquashFS overlay filesystems
• Familiarity with OpenSync or similar cloud-managed CPE frameworks (OVSDB, protobuf, MQTT telemetry)
• Experience with cellular modem integration — AT commands, QMI, network interface management (rmnet/wwan)
• Strong understanding of Linux networking — routing tables, metrics, netfilter, bridge interfaces, IPv4 and IPv6 dual-stack, neighbor discovery, DHCPv4/DHCPv6, SLAAC, and prefix delegation
• Understanding of TLS handshake with mutual authentication using X.509 certificates, certificate chain validation, and secure provisioning
• Knowledge of security and tunneling protocols — GRE tunneling, IPsec, VPN overlays, and secure encapsulation for cloud-managed traffic
• Experience with event loop frameworks (libev, libuv, or similar)
• Proficiency with debugging tools — GDB, strace, tcpdump, kernel logs, serial console
• Familiarity with Git, GitLab CI/CD, cross-compilation toolchains
• Understanding of WiFi standards (802.11ax/be) and wireless driver configuration

Preferred Skills

• Experience with Qualcomm IPQ series SoCs (IPQ5018, IPQ9574) and NSS/PPE data path
• Experience with Broadcom BCM series chipsets (BCM4908, BCM6750, BCM63178) and Memory Direct Engine (MDE) / hardware acceleration
• Knowledge of Atheros/QCA/BCM wireless chipsets and CFG80211/mac80211 driver architecture
• Knowledge of DOCSIS cable modem interaction and WAN interface management
• Experience with PCIe and USB subsystems in embedded Linux (device enumeration, power management, error recovery)
• Familiarity with eSIM/eUICC provisioning (LPA, GSMA SGP.22)
• Experience with carrier aggregation, NR5G NSA/SA, and multi-band cellular configurations
• Understanding of TR-069/TR-369 (USP) device management protocols
• Basic understanding of TR-181 data model for CPE device management and service configuration
• Experience with Kconfig-based build configuration
• Knowledge of flash storage considerations — wear leveling, persistent partitions, factory reset flows
• Familiarity with thermal management and power management (battery-powered CPE)

Tools & Technologies

• Networking: iproute2, iptables/nftables, ovsdb-server, hostapd/wpa_supplicant, GRE, IPsec
• Build: Make, Kconfig, OpenWrt feeds, cross-compilation (musl/glibc)
• Debug: GDB, valgrind, serial console, logpull analysis
• VCS/CI: Git, GitLab, merge request workflows

Nice to Have

• Experience working directly with ISP/MSO/OEM partners
• Exposure to hardware bring-up and board support package (BSP) development
• Experience with Agile/Scrum in a firmware development context
• Familiarity with SCTE/DOCSIS standards
• Understanding of TR-181 data model parameters for WAN management, WiFi configuration, and device monitoring
• Experience with GRE tunnel implementation for backhaul traffic in managed WiFi deployments

What You'll Work On

• Cellular failover/fallback state machines with sub-second transition handling
• LED indication logic for multi-WAN connectivity states
• Modem health monitoring and subsystem restart/recovery
• Internet reachability healthcheck frameworks
• Cloud-managed device configuration and telemetry reporting via MQTT
• Secure cloud connectivity using mTLS with X.509 certificate-based mutual authentication
• GRE tunnel management for cloud-redirected traffic
• Factory reset, firmware upgrade, and persistent storage management
• IPv4/IPv6 dual-stack network configuration, routing, and failover across DOCSIS and LTE interfaces
• WiFi radio configuration and performance optimization across Qualcomm / Broadcom platforms
• Kernel crash analysis and driver-level bug resolution

Top Skills:

• 1. Embedded C Development on Linux/OpenWrt
• 2. OpenSync/OpenWrt Platform Development
• o OpenSync Managers, OVSDB, UCI, MQTT, OpenWrt build system

Team size 8

Direct report - None

Responsibilities

• Design, develop, and debug embedded C software for Linux-based residential gateway platforms (ARM/MIPS SoC)
• Develop and maintain OpenSync managers — event-driven daemons that interact with OVSDB for cloud-managed configuration and state reporting
• Implement and optimize LTE/5G cellular failover and fallback logic including modem management, route arbitration, and WAN healthchecks
• Develop LED state machine logic to provide accurate device status indication across complex multi-WAN scenarios
• Interface with cellular modems via AT commands, QMI/MBIM, USB, and PCIe (MHI) protocols
• Work with WiFi drivers (Qualcomm/Broadcom/Atheros) for 2.4GHz, 5GHz, and 6GHz radio configuration
• Debug kernel-level issues including PCIe enumeration, USB device management, network driver crashes, and kernel panics
• Implement and maintain secure communication channels using TLS with mutual authentication and tunneling protocols
• Analyze and resolve field issues using device logs, crash dumps, and remote diagnostics
• Develop init scripts, UCI configuration handlers, and persistent storage management for OpenWrt
• Write unit tests and participate in code reviews via GitLab merge requests
• Collaborate with hardware teams, QA, cloud platform engineers, and service provider partners

unique selling points - Strong - Hands-on experience developing OpenSync-based OpenWrt gateway firmware with LTE/5G cellular failover, combining deep Embedded C expertise, Linux networking, and cloud-managed CPE platforms.