Add feature defmt-timestamp-uptime

Enabling it adds a timestamp of the number of seconds since startup next
to defmt log messages using `Instant::now`.

embassy/Cargo.toml

@@ -17,6 +17,10 @@ nightly = ["embedded-hal-async"]
 # Implement embedded-hal-async traits if `nightly` is set as well.
 unstable-traits = ["embedded-hal-1"]
 
+# Display a timestamp of the number of seconds since startup next to defmt log messages
+# To use this you must have a time driver provided.
+defmt-timestamp-uptime = ["defmt"]
+
 # Enable `embassy::time` module. 
 # NOTE: This feature is only intended to be enabled by crates providing the time driver implementation.
 # Enabling it directly without supplying a time driver will fail to link.

embassy/src/fmt.rs

@@ -195,6 +195,10 @@ macro_rules! unwrap {
     }
 }
 
+#[cfg(feature = "defmt-timestamp-uptime")]
+// defmt offers a disply hint for microseconds so we convert from millis
+defmt::timestamp! {"{=u64:us}", crate::time::Instant::now().as_millis() * 1_000 }
+
 #[derive(Debug, Copy, Clone, Eq, PartialEq)]
 pub struct NoneError;