Macro write_sysreg 

macro_rules! write_sysreg {
    ($sysreg:ident $(: $asm_sysreg:tt)?, $type:ty, safe, $fake_sysregs:expr) => { ... };
    (
        $(#[$attributes:meta])*
        $sysreg:ident $(: $asm_sysreg:tt)?, $type:ty, $fake_sysregs:expr
    ) => { ... };
    ($sysreg:ident $(: $asm_sysreg:tt)?, $type:ty : $bitflags_type:ty, safe, $fake_sysregs:expr) => { ... };
    (
        $(#[$attributes:meta])*
        $sysreg:ident $(: $asm_sysreg:tt)?, $type:ty : $bitflags_type:ty, $fake_sysregs:expr
    ) => { ... };
}

Generates a public function named write_$sysreg to write to the fake system register $sysreg of type $type.