Allow listing and selecting probe

This provides options similar to cargo-flash to list all connected probes
and to specify which one to use:
  probe-run --list-probes
  probe-run --probe '1366:0101' --chip nrf52 bin
  probe-run --probe '1366:0101:123456' --chip nrf52 bin

This also alows specifying the probe as en env-var:
  PROBE_RUN_PROBE='1366:0101:123456' cargo run

It fixes knurling-rs#14.

README.md

@@ -44,6 +44,16 @@ To support multiple devices, or permit overriding default behavior, you may pref
 `${PROBE_RUN_CHIP}` environment variable, and set `runner` (or
 `CARGO_TARGET_${TARGET_ARCH}_RUNNER`) to `probe-run`.
 
+If you have several probes connected, you can specify which one to use adding
+the --probe option to the `runner` or setting the `${PROBE_RUN_PROBE}` environment
+variable:
+
+```console
+PROBE_RUN_PROBE='1366:0101:123456' cargo run
+```
+
+To list all connected probes run `probe-run --list-probes`.
+
 2. Enable debug info
 
 Next check that debug info is enabled for all profiles.

src/main.rs

@@ -50,17 +50,25 @@ struct Opts {
     #[structopt(long)]
     list_chips: bool,
 
+    /// Lists all the connected probes and exit.
+    #[structopt(long)]
+    list_probes: bool,
+
     /// Enable defmt decoding.
     #[cfg(feature = "defmt")]
     #[structopt(long, conflicts_with = "no_flash")]
     defmt: bool,
 
     /// The chip to program.
-    #[structopt(long, required_unless("list-chips"), env = "PROBE_RUN_CHIP")]
+    #[structopt(long, required_unless_one(&["list-chips", "list-probes"]), env = "PROBE_RUN_CHIP")]
     chip: Option<String>,
 
+    /// The probe to use (eg. VID:PID or VID:PID:Serial).
+    #[structopt(long, env = "PROBE_RUN_PROBE")]
+    probe: Option<String>,
+
     /// Path to an ELF firmware file.
-    #[structopt(name = "ELF", parse(from_os_str), required_unless("list-chips"))]
+    #[structopt(name = "ELF", parse(from_os_str), required_unless_one(&["list-chips", "list-probes"]))]
     elf: Option<PathBuf>,
 
     /// Skip writing the application binary to flash.
@@ -73,6 +81,10 @@ fn notmain() -> Result<i32, anyhow::Error> {
 
     let opts: Opts = Opts::from_args();
 
+    if opts.list_probes {
+        return print_probes();
+    }
+
     if opts.list_chips {
         return print_chips();
     }
@@ -221,7 +233,12 @@ fn notmain() -> Result<i32, anyhow::Error> {
         bail!("no probe was found")
     }
     log::debug!("found {} probes", probes.len());
-    let probe = probes[0].open()?;
+    let probe = if let Some(probe_opt) = opts.probe.as_deref() {
+        let selector: probe_rs::DebugProbeSelector = probe_opt.try_into()?;
+        probe_rs::Probe::open(selector)?
+    } else {
+        probes[0].open()?
+    };
     log::info!("opened probe");
     let mut sess = probe.attach(target)?;
     log::info!("started session");
@@ -624,6 +641,22 @@ fn backtrace(
     Ok(top_exception)
 }
 
+fn print_probes() -> Result<i32, anyhow::Error> {
+    let probes = Probe::list_all();
+
+    if !probes.is_empty() {
+        println!("The following devices were found:");
+        probes
+            .iter()
+            .enumerate()
+            .for_each(|(num, link)| println!("[{}]: {:?}", num, link));
+    } else {
+        println!("No devices were found.");
+    }
+
+    Ok(0)
+}
+
 fn print_chips() -> Result<i32, anyhow::Error> {
     let registry = registry::families().expect("Could not retrieve chip family registry");
     for chip_family in registry {