ARM, RISC-V контроллеры

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You can use named register variables to access registers of an ARM architecture-based processor.

Named register variables are declared by combining the register keyword with the __asm keyword. The __asm keyword takes one parameter, a character string, that names the register. For example, the following declaration declares R0 as a named register variable for the register r0:
register int R0 __asm("r0");
Any type of the same size as the register being named can be used in the declaration of a named register variable. The type can be a structure, but bitfield layout is sensitive to endianness.
You must declare core registers as global rather than local named register variables. Your program might still compile if you declare them locally, but you risk unexpected runtime behavior if you do. There is no restriction on the scope of named register variables for other registers.

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