Very stimulating but calm interview with a Senior Engineer. Went through my abilities/skills and what I thought I could do at the company. Worked through an exercise to determine what a function was doing. This tested understanding of C code and typical bare-metal fundamentals like bit-shifting etc. as well as demonstrated your ability to grasp the larger objective of a function. The HR interview was pretty standard and fair. They're not looking for just anybody to fill a role; they highly value their company culture and want people who contribute to it.