An ARM Cortex developer designs and implements software for devices using the ARM Cortex- microcontroller. They write code in languages like C or Assembly, and are responsible for testing, debugging, and optimizing this code to ensure optimal performance. Developers work on different aspects such as system initialization, peripheral driver development, and real-time operating system (RTOS) integration. They must understand the hardware to optimize power consumption and memory usage. They also work with hardware engineers to define requirements and functionalities, and often participate in code reviews to maintain code quality. They must also troubleshoot and fix any software issues.