C/C++ is the language, named in most job posts and in nearly all at the chip and network companies. Embedded C is named separately where the job is plain C on a small microcontroller with no operating system at all, and Assembler appears at the processor makers and in big tech, where the engineer reads what the compiler produced or writes the first instructions a chip runs. Rust appears in a handful of job posts. Python is assumed for the scripts and tests around the firmware.
The chip itself is named. ARM is the processor family in most devices and is named in a fair share of job posts, RISC-V is the newer open architecture appearing at the processor makers and in big tech, and x86 appears at the server makers. SoC, the system on a chip that packs processor, memory and peripherals together, and Microcontrollers, the small chips that run a single job, name the two ends of the hardware the engineer writes for. FPGA appears where the firmware sits beside programmable logic, at the network and server makers.
A firmware engineer's everyday work is making the chip talk to the parts around it, and the buses and protocols that carry those conversations are named as skills in their own right. I2C and SPI are the two short-distance buses that connect a chip to its sensors, memory and displays, and they are named in a fair share of job posts and in most of the microcontroller ones. UART is the serial line used for consoles and simple links, USB connects the device to a host, PCIe connects high-speed cards and is named most at the network, server and processor companies, Ethernet and TCP/IP connect the device to a network, and Bluetooth connects it to a phone. DMA moves data without the processor's help. Writing the code that drives each of these is what a job post means by Device Drivers, which is one of the most-named skills in the role.
The smallest devices run with no operating system. The firmware starts when the power comes on, sets up the chip, and runs a loop forever. Bootloaders are the first code a device runs, and writing them is named in a fair share of job posts, with Das U-Boot as the common one for Linux boards and Secure Boot where the device must prove its software has not been tampered with, most at the network and server makers. Where the device has to do several things at once with strict timing, it runs a real-time operating system, and RTOS is named in a large share of job posts, most at the chip-equipment makers, the industrial companies and the sensor-chip makers. FreeRTOS is the open one, VxWorks the long-standing commercial one in aerospace and industry, and QNX the one the car industry runs its safety-critical and infotainment systems on, named most in automotive and Android platform job posts. HAL, the hardware abstraction layer, is the code that hides the chip's details from everything above it.
Larger devices run Linux, slimmed down and fitted to the board, and this is the second most-named family of skills after C/C++. Embedded Linux is the slimmed-down system, Linux BSP is the board support package that makes the kernel run on a particular board, and the Linux Kernel and Linux Device Drivers are the kernel work itself, the same skills a systems engineer has but applied to one device. Yocto and Buildroot are the tools for building a custom Linux image for a board, and Yocto is named most at the industrial companies and the engineering services firms. Embedded Linux leads at the processor makers, where the work is drivers and board support for the company's own chips, at the network equipment makers, for switches, routers and access points, and at the server makers, whose management controllers run Linux before the server's own operating system starts.
A smaller set of job posts work on Android below the apps, in the layer that makes Android run on a particular phone, car dashboard or gadget. AOSP, the Android Open Source Project, is the source code itself, and it is named in most of these job posts. The Android Framework is the layer the apps call, HAL and HIDL are the interfaces between Android and the hardware drivers, the AOSP Build System builds it all, and NDK lets C/C++ code run inside Android. This work sits on top of the Linux Kernel and Linux Device Drivers, which is why those are named in most Android platform job posts too. It is concentrated at the processor makers, which make Android run on their chips, the car-dashboard companies, which build infotainment on Android Automotive, and at Amazon's devices group.
Automotive software is a specialism with its own vocabulary, and the car-parts companies, the car-dashboard companies, the carmakers' GCCs and the engineering services firms ask for it. CAN Bus is the network inside a car that its control units talk over, with LIN for the simpler links and Ethernet and SOME/IP for the newer high-speed ones, and CAN Bus is named in most automotive job posts. AUTOSAR is the standard architecture for the software on a car's control units, and it is the core of the parts companies' job posts. ISO 26262 is the functional-safety standard that governs how software that could hurt someone is written and tested, and ASPICE is the process standard that carmakers audit their suppliers against. Both are named in a large share of automotive job posts, and they shape every line of code. Vector CANoe, CANalyzer and CAPL are the tools for testing and simulating the car's network, dSPACE runs hardware-in-the-loop tests, and Simulink is where control logic is modelled before it becomes code. Engineering software and CAD are tagged most on these job posts.
Firmware is debugged on real hardware, and the tools of the bench are named as skills. JTAG is the debug port on the chip, and Lauterbach and TRACE32 are the hardware debuggers that use it. GDB is the software debugger. An Oscilloscope and a Logic Analyzer show what the signals on the wires are actually doing, and they are named in a fair share of job posts, most at the processor makers and the industrial companies. Testing is tagged on a large share of job posts, most at the industrial companies, the automotive companies and in big tech, and it means hardware-in-the-loop rigs, test automation in Python with Robot Framework, and the lab equipment above.
Firmware is built with a cross-compiler for a chip other than the one it is built on, and build and release is the most common extra tag in the role, on a large share of job posts, most at the industrial companies, the automotive companies and the engineering services firms. It means the build systems, Yocto and the AOSP Build System among them, Jenkins, GitHub Actions, GitLab CI/CD and Azure DevOps where a pipeline carries the result, Docker where the build runs in a container so every engineer gets the same toolchain, and Git throughout. Release means flashing an image onto a device, and over-the-air updates where the device is in the field.
A small share of job posts reach into neighbouring work. Security is tagged on a fair share, most at the network and server makers, and means Secure Boot, encryption on the device and hardening the firmware against attack. Machine learning on the device, tagged most at the processor makers, means running a model on the chip with ONNX, NVIDIA TensorRT or OpenCV. Wireless protocols, Bluetooth, MQTT, 5G and LTE, appear at the connectivity-chip companies, the device makers and in big tech. Modbus and SCADA appear at the industrial companies, for talking to factory equipment. Cloud and containers are tagged on a small share, most at the network makers whose products now connect to a cloud service. In the ordinary firmware job these are a plus.
Underneath all of it sits the way firmware is built: Git and code review, a release tied to a hardware revision, every requirement traced to a test in the regulated industries, and long hours on the bench finding out why the signal on the wire is not what the code expected. Job posts count these as given and rarely list them as skills.
A firmware engineer who writes C/C++ well, has brought up a board from the Bootloader through Embedded Linux or an RTOS, can write a Device Driver for I2C, SPI, UART or PCIe, knows ARM, debugs with JTAG and GDB, and can read an Oscilloscope, meets the core of nearly every job post. The variations belong to the employer. The processor makers want Linux Device Drivers, Linux BSP and AOSP for their own chips, with Assembler, RISC-V and machine learning on the device, and they are the largest home. The sensor-chip and chip-equipment makers want RTOS and microcontroller work, and they are the most open to juniors. The car-parts companies and carmakers' GCCs want AUTOSAR, CAN Bus, ISO 26262, ASPICE and the Vector tools, and the dashboard companies want Android Automotive and QNX on top. The network and server makers want Embedded Linux, drivers, PCIe, Layer 2 and Layer 3, Secure Boot and FPGA. The industrial, aerospace and medical-device companies want RTOS, Yocto, the bench tools and the most testing, with the standards of their industries. Big tech wants firmware for its own devices, with 5G, LTE, Bluetooth and SoC work. The engineering services firms are the main services door and ask for the whole set, automotive above all. Across all of them, the engineer who can make a chip do what the datasheet says it should is the one every job post describes.