Merge #547

547: Migration guide `v0.2.x` to `v0.3.0` r=japaric a=Urhengulas Migration guide from `defmt v0.2.x` to version `v0.3.0`. https://deploy-preview-547--admiring-dubinsky-56dff5.netlify.app/migration-02-03.html Fixes #530. ### TODO - [x] #505: Logger trait v2 - [x] #521: [3/n] Remove u24 - [x] #522: Replace `µs` hint with `us` - [x] (no adaption needed) ~~#508: [5/n] Format trait v2~~ - [x] #519: `DEFMT_LOG` - [x] #550: `defmt::flush()` - [x] knurling-rs/probe-run#198, knurling-rs/probe-run#250, Co-authored-by: Johann Hemmann <[email protected]>
knurling-rs · Oct 19, 2021 · da1682f · da1682f
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diff --git a/book/src/SUMMARY.md b/book/src/SUMMARY.md
@@ -16,6 +16,7 @@
   - [panic! and assert!](./panic.md)
   - [Printers](./printers.md)
   - [Encoding](./encoding.md)
+- [Migrating from `v0.2.x` to `v0.3.0`](./migration-02-03.md)
 - [Design & impl details](./design.md)
   - [Interning](./interning.md)
     - [Dealing with duplicates](./duplicates.md)

diff --git a/book/src/migration-02-03.md b/book/src/migration-02-03.md
@@ -0,0 +1,311 @@
+# Migrating from `v0.2.x` to `v0.3.0`
+
+This guide covers how to upgrade a library or application using `defmt v0.2.x` to version `v0.3.0`.
+
+## `Cargo.toml`
+
+Update the version of `defmt` to `"0.3"` (or `"0.3.0"`, which is equivalent).
+
+Additionally please remove the `defmt-*` cargo features from your `[features]` section.
+
+```diff
+[dependencies]
+
+- defmt = "0.2"
++ defmt = "0.3"
+
+[features]
+default = [
+    "other-feature",
+-   "defmt-default",
+-   "dependency-a/defmt-trace",
+]
+
+other-feature = []
+
+- defmt-default = []
+- defmt-trace = []
+- defmt-debug = []
+- defmt-info = []
+- defmt-warn = []
+- defmt-error = []
+```
+
+## Set the log-level with `DEFMT_LOG`
+
+Setting the log-level via cargo features is superseded by the new `DEFMT_LOG` environment variable.
+
+To log everything on the `INFO` level and above, run your application like following:
+
+```console
+$ DEFMT_LOG=info cargo run
+```
+
+For more details how to configure the log-level using `DEFMT_LOG` see the [user docs](./filtering.md#defmt_log).
+
+This new mechanism is modelled to be similar to the well-known `RUST_LOG` and now also supports log-configuration down to the module-level!
+
+## Upgrade display hints
+
+> 💡 Easily change the display hints, using the search-and-replace feature of your editor. *([vs code](https://code.visualstudio.com/docs/editor/codebasics#_search-and-replace))*
+
+### Rename display hint `µs` to `us`
+
+Due to ambiguity in-between `µ` (micro sign) and `μ` (small mu), the display hint for microseconds changed to be `us`.
+
+Therefore you likely need to update your timestamp definition.
+
+```diff
+- defmt::timestamp!("{=u32:µs}", {
++ defmt::timestamp!("{=u32:us}", {
+    // ...
+});
+```
+
+As well as all other logging calls where you were using `µs`.
+
+```diff
+- defmt::info!("{=u8:µs}", time)
++ defmt::info!("{=u8:us}", time)
+```
+
+### Drop `u24` type hint
+
+The `u24` type hint got dropped, cause it was confusing users and complicated internal parser logic.
+
+Therefore replace it with `u32` in all logging calls.
+
+```diff
+- defmt::info!("{=u24}", 42);
++ defmt::info!("{=u32}", 42);
+```
+
+## Adapt manual `trait Logger` implementations
+
+The `Logger` trait has seen a couple of big changes, for one the function signatures of a few methods have changed, the previous `Write` trait got removed while its `write` method is part of `Logger` now and the method `flush` was added.
+
+> 💡 If you are using one of our loggers, `defmt-rtt` and `defmt-itm`, no action is required!
+
+Let's see what a new implementation of the `Logger` in crate `defmt-itm` looks like compared to the previous implementation in version `0.2`. The following abbreviated example code shows how the `Logger` worked before.
+
+```rust,ignore
+#[defmt::global_logger]
+struct Logger;
+
+static TAKEN: AtomicBool = AtomicBool::new(false);
+
+unsafe impl defmt::Logger for Logger {
+    fn acquire() -> Option<NonNull<dyn defmt::Write>> {
+        // disable interrupts
+
+        if !TAKEN.load(Ordering::Relaxed) {
+            // acquire the lock
+            TAKEN.store(true, Ordering::Relaxed);
+            Some(NonNull::from(&Logger as &dyn defmt::Write))
+        } else {
+            None
+        }
+    }
+
+    unsafe fn release(_: NonNull<dyn defmt::Write>) {
+        // release the lock
+        TAKEN.store(false, Ordering::Relaxed);
+
+        // re-enable interrupts
+    }
+}
+
+impl defmt::Write for Logger {
+    fn write(&mut self, bytes: &[u8]) {
+        unsafe { itm::write_all(&mut (*ITM::ptr()).stim[0], bytes) }
+    }
+}
+```
+
+And here is how it conceptually works now:
+
+```rust
+# extern crate defmt;
+# use std::sync::atomic::{AtomicBool,Ordering};
+
+#[defmt::global_logger]
+struct Logger;
+
+static TAKEN: AtomicBool = AtomicBool::new(false);
+static mut ENCODER: defmt::Encoder = defmt::Encoder::new();
+
+unsafe impl defmt::Logger for Logger {
+    fn acquire() {
+        // disable interrupts
+
+        if TAKEN.load(Ordering::Relaxed) {
+            panic!("defmt logger taken reentrantly")
+        }
+
+        // acquire the lock
+        TAKEN.store(true, Ordering::Relaxed);
+
+        unsafe { ENCODER.start_frame(do_write) }
+    }
+
+    unsafe fn flush() {
+        // Omitted. We will come to this in a second.
+    }
+
+    unsafe fn release() {
+        ENCODER.end_frame(do_write);
+
+        // release the lock
+        TAKEN.store(false, Ordering::Relaxed);
+
+        // re-enable interrupts
+    }
+
+    unsafe fn write(bytes: &[u8]) {
+        ENCODER.write(bytes, do_write);
+    }
+}
+
+fn do_write(bytes: &[u8]) {
+    unsafe { itm::write_all(&mut (*ITM::ptr()).stim[0], bytes) }
+}
+
+# // mock cortex_m-crate
+# mod itm {
+#     pub unsafe fn write_all(a: &mut u8, b: &[u8]) {}
+# }
+# struct ITM { stim: [u8; 1] }
+# impl ITM {
+#     fn ptr() -> *mut ITM { &mut ITM { stim: [0] } as *mut _ }
+# }
+```
+
+Let us go through the changes step-by-step:
+- Drop `trait Write`:
+  - Extract the `fn write` from the `trait Write` and name it `fn do_write`.
+  - Remove the `impl defmt::Write for Logger`.
+  - Remove the the first argument of `&mut self` from `fn do_write`.
+- Add a new `static mut ENCODER: defmt::Encoder = defmt::Encoder::new()` outside the `impl defmt::Logger for Logger`-block.
+- Adapt `fn acquire`:
+  - Remove the return type `Option<NonNull<dyn defmt::Write>>` from `fn acquire`.
+  - Replace all `return None` with an explicit `panic!`, with a descriptive error message.
+  - Call `unsafe { ENCODER.start_frame(do_write) }`, after you acquired the lock.
+- Adapt `fn release`:
+  - Call `ENCODER.end_frame(do_write);`, before releasing the lock.
+- Add new method `unsafe fn write` to `impl defmt::Logger for Logger`:
+    ```rust,noplayground
+    # extern crate defmt;
+    # static mut ENCODER: defmt::Encoder = defmt::Encoder::new();
+    # fn do_write(bytes: &[u8]) {}
+    unsafe fn write(bytes: &[u8]) {
+        ENCODER.write(bytes, do_write);
+    }
+    ```
+
+And that is already it!
+
+### Flush
+
+One final thing is left before your custom `trait Logger` implementation works again: You need to implement `fn flush`.
+
+This functionality is what gets used when calling `defmt::flush`, [whose docs say](https://docs.rs/defmt/*/defmt/fn.flush.html):
+> Block until host has read all pending data.
+>
+> The flush operation will not fail, but might not succeed in flushing all pending data. It is implemented as a “best effort” operation.
+
+The idea is to ensure that _all data_ is read by the host. Take `defmt-rtt` as an example:
+
+```rust
+# extern crate defmt;
+# use std::sync::atomic::{AtomicUsize,Ordering};
+
+# #[defmt::global_logger]
+# struct Logger;
+
+# static READ: AtomicUsize = AtomicUsize::new(0);
+# static WRITE: AtomicUsize = AtomicUsize::new(0);
+
+unsafe impl defmt::Logger for Logger {
+    fn acquire() {
+        // ...
+    }
+
+    unsafe fn flush() {
+        // busy wait, until the read- catches up with the write-pointer
+        let read = || READ.load(Ordering::Relaxed);
+        let write = || WRITE.load(Ordering::Relaxed);
+        while read() != write() {}
+    }
+
+    unsafe fn release() {
+        // ...
+    }
+
+    unsafe fn write(bytes: &[u8]) {
+        // ...
+    }
+}
+```
+
+If your transport doesn't allow to ensure that _all data_ got read, `flush` should at least flush _as much data as possible_. Take `defmt-itm` as an example for this:
+
+```rust
+# extern crate defmt;
+
+# #[defmt::global_logger]
+# struct Logger;
+
+unsafe impl defmt::Logger for Logger {
+    fn acquire() {
+        // ...
+    }
+
+    unsafe fn flush() {
+        // wait for the queue to be able to accept more data
+        while !stim_0().is_fifo_ready() {}
+
+        // delay "a bit" to drain the queue
+        // This is a heuristic and might be too short in reality.
+        // Please open an issue if it is!
+        asm::delay(100);
+    }
+
+    unsafe fn release() {
+        // ...
+    }
+
+    unsafe fn write(bytes: &[u8]) {
+        // ...
+    }
+}
+
+# // mock cortex_m-crate
+# struct STIM0;
+# impl STIM0 {
+#     fn is_fifo_ready(&self) -> bool { true }
+# }
+# fn stim_0() -> STIM0 { STIM0 }
+# mod asm {
+#     pub fn delay(cycles: usize) {}
+# }
+```
+
+`defmt::flush` can be used before a hard-reset of the device, where you would loose data if you do not flush.
+
+Since you are the expert of your transport, implement the method now!
+
+## Unified `probe-run` backtrace options
+
+The new `--backtrace` and `--backtrace-limit` of `probe-run` should simplify the configuration.
+
+```console
+cargo run --bin panic --backtrace=always --backtrace-limit=5
+```
+
+Using `--backtrace` you can now specify if you want to have a backtrace `never`, `always` or only in case of an exception (the `auto` option, which is the default). For the latter two options you can specify the maximum backtrace length, which defaults to `50` and can be set to unlimited with `0`.
+
+See [the `probe-run`-README](https://github.com/knurling-rs/probe-run#backtrace-options) for all the options.
+
+## Congrats! 🎉
+
+If you followed all the steps in this guide, your application should work flawlessly again and make use of all the internal and user-facing improvements shipped in this release! 
diff --git a/book/src/primitives.md b/book/src/primitives.md
@@ -2,14 +2,14 @@
 
 The following **primitive types** are available:
 
-| type hint            | name                                |
-| :------------------- | :---------------------------------- |
-| `=bool`              | boolean                             |
-| `={i,u}{8,16,32,64}` | standard integer types              |
-| `=f{32, 64}`         | 32-bit / 64-bit floating point type |
-| `=[u8; N]`           | byte array                          |
-| `=[u8]`              | byte slice                          |
-| `=str`               | string slice                        |
+| type hint                | name                                |
+| :----------------------- | :---------------------------------- |
+| `=bool`                  | boolean                             |
+| `={i,u}{8,16,32,64,128}` | standard integer types              |
+| `=f{32, 64}`             | 32-bit / 64-bit floating point type |
+| `=[u8; N]`               | byte array                          |
+| `=[u8]`                  | byte slice                          |
+| `=str`                   | string slice                        |
 
 They can be used like this:
 

diff --git a/xtask/src/main.rs b/xtask/src/main.rs
@@ -387,7 +387,14 @@ fn test_book() {
     do_test(|| run_command("cargo", &["clean"], None, &[]), "book");
 
     do_test(
-        || run_command("cargo", &["build", "--features", "unstable-test"], None, &[]),
+        || {
+            run_command(
+                "cargo",
+                &["build", "-p", "defmt", "--features", "unstable-test"],
+                None,
+                &[],
+            )
+        },
         "book",
     );