If you've never done embedded development before I highly recommend the two parts MOOC "Embedded Systems - Shape The World"[1].
The course is well structured, teaching the basics you'll need for those boards that doesn't usually have an OS and requires a ~40$ components kit that include a Texas Instruments board.
Quite fun if you follow along and do all the exercises.
Upvoting this as I just started following this course myself (archived but all the material
Is still available). The kit is self sufficient and with some basic C programming skills one gets cut their teeth on all relevant real world embedded design methodologies. I am also taking the NAND2TETRIS course in parallel and can now start appreciating the hardware/software interface. Highly recommend that course and the accompanying book.