Bitfields

:m..n is the bitfield formatting parameter. When paired with a positional parameter it can be used to display the bitfields of a register.

#![allow(unused)]
fn main() {
extern crate defmt;
let pcnf1 = 0u32;
// -> TRACE: PCNF1 { MAXLEN: 125, STATLEN: 3, BALEN: 0b010 }
defmt::trace!(
    "PCNF1: {{ MAXLEN: {0:0..8}, STATLEN: {0:8..16}, BALEN: {0:16..19} }}",
    //                  ^                  ^                 ^ same argument
    pcnf1, // <- type must be `u32`
);
}

The bitfield argument is expected to be a fully typed, unsigned integer that's large enough to contain the bitfields. For example, if bitfield ranges only cover up to bit 11 (e.g. :8..12) then the argument must be u16.

Bit indices are little-endian: the 0th bit is the rightmost bit.

Bitfields are not range inclusive, e.g.

#![allow(unused)]
fn main() {
extern crate defmt;
defmt::trace!("first two bits: {0:0..3}", 254u32);
}

will evaluate to 0b10.

⚠️ You can not reuse the same argument in a bitfield- and a non bitfield parameter. This will not compile:

#![allow(unused)]
fn main() {
extern crate defmt;
defmt::trace!("{0:5..13} {0:u16}", 256u16);
}