sources/tty: apply user-supplied baud rate

Before this commit, dev in

    --serial /path/to/dev

would always be configured for 115200 B/s, even if the user supplied
another rate in the manifest via tpiu_baud, e.g. 9600 B/s. A baud rate
that converts to a nix::sys::termios::BaudRate that isn't B0 must be
supplied.

Ideally we should CI this, but that requires a CI refactor so that
--serial can be specified. This is non-trivial, and we better handle #77
first.

CHANGELOG.md

@@ -8,6 +8,19 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ### Added
 - `/docs/`, a submodule that contains the overarching documentation of RTIC Scope, which is rendered at [the organization profile](https://github.com/rtic-scope).
 
+### Changed
+- On `--serial /path/to/dev`, `dev` will no longer unconditionally configure for 115200 B/s; the baud rate specified with `tpiu_baud` in the `[package.metadata.rtic-scope]` block in `Cargo.toml` will instead be applied.
+  For example, `tpiu_baud = 9600` will configure `dev` for 9600 B/s.
+  Valid baud rates are listed in [`nix::sys::termios::BaudRate`](https://docs.rs/nix/0.23.1/nix/sys/termios/enum.BaudRate.html), with the exception of `B0`.
+
+### Deprecated
+
+### Removed
+
+### Fixed
+
+### Security
+
 ## [0.3.0] - 2022-01-05
 Initial release tracked by this changelog.
 

cargo-rtic-scope/src/main.rs

@@ -708,7 +708,8 @@ async fn trace(
 
     let trace_source: Box<dyn sources::Source> = if let Some(dev) = &opts.serial {
         Box::new(sources::TTYSource::new(
-            sources::tty::configure(dev).with_context(|| format!("Failed to configure {}", dev))?,
+            sources::tty::configure(dev, manip.tpiu_baud)
+                .with_context(|| format!("Failed to configure {}", dev))?,
             &manip,
         ))
     } else {

cargo-rtic-scope/src/sources/tty.rs

@@ -34,13 +34,21 @@ mod ioctl {
 ///
 /// Effectively mirrors the behavior of
 /// ```
-/// $ screen /dev/ttyUSB3 115200
+/// $ screen /dev/ttyUSB3 <baud rate>
 /// ```
 /// assuming that `device` is `/dev/ttyUSB3`.
 ///
 /// TODO ensure POSIX compliance, see termios(3)
 /// TODO We are currently using line disciple 0. Is that correct?
-pub fn configure(device: &str) -> Result<fs::File, SourceError> {
+pub fn configure(device: &str, baud_rate: u32) -> Result<fs::File, SourceError> {
+    // ensure a valid baud rate was requested
+    let baud_rate: BaudRate = baud_rate
+        .try_into()
+        .map_err(|_| SourceError::SetupError(format!("{} is not a valid baud rate", baud_rate)))?;
+    if baud_rate == BaudRate::B0 {
+        return Err(SourceError::SetupError("baud rate cannot be 0".to_string()));
+    }
+
     let file = fs::OpenOptions::new()
         .read(true)
         .open(&device)
@@ -143,7 +151,7 @@ pub fn configure(device: &str) -> Result<fs::File, SourceError> {
             | LocalFlags::PENDIN
             | LocalFlags::NOFLSH);
 
-        termios::cfsetspeed(&mut settings, BaudRate::B115200).map_err(|e| {
+        termios::cfsetspeed(&mut settings, baud_rate).map_err(|e| {
             SourceError::SetupError(format!(
                 "Failed to configure {} baud rate: cfsetspeed = {}",
                 device, e