Shawn Silverman

Making this a draft for now.

This commit also makes sure each copy constructor has a sibling `operator=()`.

There's two checks anyway, would a fix really slow this down?

Understood. That’s a very interesting reason. (Today I learned.) :)

It turns out that without the fix, the transmit properly sends 7-bit data, but receive still sometimes sets the 8th bit high. I need to explore more...

See: https://github.com/PaulStoffregen/cores/pull/665#issuecomment-1320067423 The last bit in the stream is the parity bit, and is also the top bit in the byte.

I believe the issue also appears in teensy3 serial. I updated the PR with a second commit to fix that too.

Note that the commit message isn't exactly the same as the PR description. See if it's acceptable to you.

Is there no chance of reordering, then, even with future compilers? Or maybe even the lines with `:::“memory”` can’t be reordered?

Thanks, @tsandmann. That makes it a little more clear. Is there even a way to disable reordering for these statements? Update: or maybe the compiler considers the “dsb” instruction non-reorderable?