Embedded Systems Security is a practical training on black box evaluations of embedded systems. The training starts with an introduction to security theory, and quickly moves to practical content on hacking embedded Linux devices, and defending them. In particular, with physical access to the hardware in scope. https://www.keysight.com/us/en/learn/bootcamp/164386.html
If you are a hacker, but don't yet have experience with embedded systems, this training is worth your while. The training is designed to give an in depth understanding of electronic devices and how to attack them. The examples are not extreme, and teach you the ideas and methods instead of giving you a list of exploits. While my contribution is as part of a team, the training contains some of my best writing I've done. Many chapters on hardware, components, circuit boards, and low level communication are mine. I'm thrilled the training is now available for everyone, online, and free.