Macro write_sysreg 

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

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

safe should only be specified for system registers which are indeed safe to write any value to.