So maybe everyone but me knows this, but what's the behavior of bitfields on the bus? Like, if r.x is the bottom 6 bits of a 32-bit register, then does the comp

So maybe everyone but me knows this, but what's the behavior of bitfields on the bus? Like, if r.x is the bottom 6 bits of a 32-bit register, then does the compiler generate an 8-bit access or a 32-bit access? What if it's bits 13 through 18? An unaligned 16-bit access? Two 8-bit? A 32-bit? Where is this specified? Depending how your peripheral is implemented, this absolutely can matter. Nothing stops you from building devices where the low byte of *((uint32_t *)x) doesn't work like *((uint8_t *)x) and people do. I always just code the 32-bit access and pull the bits out myself, because I know what will happen. This is even before considering stuff like a GPIO output implemented with two write-only registers, where 0 leaves the bit unchanged and 1 sets/clears it. The result of layering a bitfield on that does not seem intuitive to me. The article also says that you should build abstraction layers for your peripherals, instead of making all your code write to registers everywhere. That seems (a) pretty well-settled as true, and (b) entirely independent of whether you do the register accesses with bitfields or explicit shifts and masks.