Macro register_bitfields

macro_rules! register_bitfields {
    {
        $valtype:ident, $( $(#[$inner:meta])* $vis:vis $reg:ident $fields:tt ),* $(,)?
    } => { ... };
}

Define register types and fields.

Implementations of memory-mapped registers can use this macro to define the structure and bitwise meaning of individual registers in the peripheral. An example use for a hypothetical UART driver might look like:

register_bitfields![u32,
    CONTROL [
        ENABLE OFFSET(0) NUMBITS(1),
        STOP_BITS OFFSET(1) NUMBITS(2) [
            StopBits1 = 0,
            StopBits2 = 1,
            StopBits0 = 2
        ]
    ],
    BYTE [
        CHARACTER OFFSET(0) NUMBITS(8)
    ],
    INTERRUPT [
        TRANSMITTED OFFSET(0) NUMBITS(1),
        RECEIVED OFFSET(1) NUMBITS(1),
        FIFO_FULL OFFSET(2) NUMBITS(1)
    ]
];

Each field in the register can be identified by its offset within the register and its bitwidth. Fields that have discrete options with semantic meaning can be enumerated.