Bitfields

=M..N is the bitfield formatting parameter.

The bitfield argument is expected to be an 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 at least u16.

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: 2 }
defmt::trace!(
    "PCNF1: {{ MAXLEN: {0=0..8}, STATLEN: {0=8..16}, BALEN: {0=16..19} }}",
    //                  ^                  ^                 ^ same argument
    pcnf1, // <- type must be `u32`
);
}

Bitfields are not range inclusive, e.g. following statement will evaluate to 5 (0b110):

#![allow(unused)]
fn main() {
extern crate defmt;
// -> TRACE: first three bits: 110
defmt::trace!("first three bits: {0=0..3}", 254u32);
}

Important

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);
}