insv vs one-bit fields

[DJ Delorie]

>   As it would seem that as HW control/I/O registers are often
>   typically mapped into a processor's data memory address space,
>   they may be correspondingly addressable via a read/mask/write as
>   any N bit field may be?

In the case of the m32c, it has a *lot* of single-bit I/O ports, and
an entire category of single-bit-operand instructions to access them
efficiently, including bit set, clear, test, test-and-set,
test-and-clear, invert, etc.  Those opcodes even have a special
addressing mode to make accessing the I/O space more efficient
(smaller opcodes, less insn fetches, etc) and can uniquely address any
*single* bit in the first 8192 bytes (yes, the address registers are
bit offsets for those insns!)

And, of course, they're all volatile.