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In order to use more advanced features or optimize our code for space and speed, we need to understand how to work with registers directly in microcontrollers.
If you're looking to learn more about how your Arduino works, create more advanced projects using things like interrupts or optimize your code for speed and size, then you'll need to work with registers.
Registers are nothing more than storage containers for data inside a processor or microcontroller, and for many microcontrollers (like the ATmega328P), they share the same space with SRAM. A large portion of registers are simply "general purpose registers," which are just places that the program can use to store results from calculations. However, many microcontrollers have a set of "special function registers" that have hardware connections built into the die for setting up timers, toggling the voltage on pins, reading analog voltages, and so on.
In this "Adventures in Science," we describe registers, how to interact with them in Arduino, and how to control hardware using them.
Special function registers are really what make the magic behind microcontrollers. Knowing how to use them allows you to control hardware connected to the microcontroller. The Arduino framework provides a level of abstraction so you don't need to worry about working with registers, which is a blessing and a curse.
On one hand, you don't have to dig through a datasheet and learn all the register names for that microcontroller. If you were to move to a different architecture (say, stop using the 328P and start using the ESP32), you'd need to find a new datasheet and learn new register names. The abstraction is perfect if you want to make a project or prototype (i.e., you just need something to work).
On the other hand, if you are making a product and need your code to be as small and fast as possible, ditching the Arduino framework is often the way to go. If you can reduce the size of your program so that it fits on a cheaper microcontroller, you might save a few cents for each unit produced (which can add up). Additionally, if you make your program run more efficiently, that may mean less power used and more battery time!
What other reasons are there for using registers directly? How would you describe a register to someone just learning about microcontrollers? Let us know in the comments below.