Merge pull request #147 from knurling-rs/default-timestamp

Default zero timestamp

book/src/setup-app.md

@@ -47,38 +47,6 @@ The following `global_logger`s are provided as part of the project:
 
 Information about how to write a `global_logger` can be found in the [`#[global_logger]` section](./global-logger.md).
 
-## `#[timestamp]`
-
-The application must link to or define a `timestamp` function.
-All logs are timestamped; this function specifies how the timestamp is computed.
-The function must have signature `fn() -> u64`; the returned value is the timestamp in microseconds (`0` = program started).
-The function should be implemented using a non-decreasing hardware counter but here are two pure-software implementations that can be used as a placeholder:
-
-No timestamps:
-
-``` rust
-# extern crate defmt;
-#[defmt::timestamp]
-fn no_timestamp() -> u64 {
-    0
-}
-```
-
-Virtual timestamps:
-
-``` rust
-# extern crate defmt;
-# use std::sync::atomic::{AtomicUsize, Ordering};
-// WARNING may overflow and wrap-around in long lived apps
-#[defmt::timestamp]
-fn virtual_timestamp() -> u64 {
-    static COUNT: AtomicUsize = AtomicUsize::new(0);
-    COUNT.fetch_add(1, Ordering::Relaxed) as u64
-}
-```
-
-More information about how to write a `timestamp` function can be found in the [`#[timestamp]` section](./timestamp.md).
-
 ## Enabling logging
 
 All logging is *disabled* by default.

book/src/timestamp.md

@@ -1,15 +1,16 @@
 # #[timestamp]
 
-*Applications* that, directly or transitively, use any of `defmt` logging macros need to define a `#[timestamp]` function or include one in their dependency graph.
+*Applications* that, directly or transitively, use any of `defmt` logging macros may define a `#[timestamp]` function or include one in their dependency graph.
 
 All logs are timestamped.
 The `#[timestamp]` function specifies how the timestamp is computed.
+By default (if no `#[timestamp]` function is provided), a timestamp of 0 will be used.
 This function must have signature `fn() -> u64` and on each invocation *should* return a non-decreasing value.
 The function is not `unsafe` meaning that it must be thread-safe and interrupt-safe.
 
-## No timestamp
+## No timestamp (default behavior)
 
-To omit timestamp information use this `#[timestamp]` function:
+When no `#[timestamp]` function is used, defmt will use one equivalent to this:
 
 ``` rust
 # extern crate defmt;
@@ -21,7 +22,7 @@ fn timestamp() -> u64 {
 
 ## Atomic timestamp
 
-A simple `timestamp` function that does not depend on device specific features and it's good enough for development is shown below:
+A simple `timestamp` function that does not depend on device specific features and is good enough for development is shown below:
 
 ``` rust
 # extern crate defmt;

defmt.x.in

@@ -1,7 +1,8 @@
 /* exhaustively search for these symbols */
 EXTERN(_defmt_acquire);
 EXTERN(_defmt_release);
-EXTERN(_defmt_timestamp);
+EXTERN(__defmt_default_timestamp);
+PROVIDE(_defmt_timestamp = __defmt_default_timestamp);
 
 SECTIONS
 {

firmware/nrf52/src/bin/panic.rs

@@ -1,17 +1,12 @@
 #![no_std]
 #![no_main]
 
-use defmt_rtt as _; // <- global logger
 use cortex_m::asm;
 use cortex_m_rt::entry;
+use defmt_rtt as _; // <- global logger
 use nrf52840_hal as _; // <- memory layout
 use panic_probe as _; // <- panicking behavior
 
-#[defmt::timestamp]
-fn timestamp() -> u64 {
-    0
-}
-
 #[entry]
 fn main() -> ! {
     defmt::info!("main");

firmware/qemu/src/bin/log.rs

@@ -190,7 +190,13 @@ fn main() -> ! {
             y: T,
         }
 
-        defmt::info!("{:?}", S { x: Some(&48), y: 49u8 });
+        defmt::info!(
+            "{:?}",
+            S {
+                x: Some(&48),
+                y: 49u8
+            }
+        );
     }
 
     // plain generic enum

src/lib.rs

@@ -437,3 +437,8 @@ pub trait Format {
     /// Writes the defmt representation of `self` to `fmt`.
     fn format(&self, fmt: &mut Formatter);
 }
+
+#[export_name = "__defmt_default_timestamp"]
+fn default_timestamp() -> u64 {
+    0
+}