Add github CI, improve README

This also fixes up runner.sh for the new(ish) VPN layout.

.github/workflows/ci.yml

@@ -0,0 +1,25 @@
+# Reference:
+# - https://doc.rust-lang.org/stable/clippy/continuous_integration/github_actions.html
+# - https://github.com/actions/starter-workflows/blob/main/ci/rust.yml
+on: push
+
+name: Clippy check
+
+# Make sure CI fails on all warnings, including Clippy lints
+env:
+  RUSTFLAGS: "-Dwarnings"
+  CARGO_TERM_COLOR: always
+
+jobs:
+  clippy_check:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - name: Build
+        run: cargo build --verbose
+      - name: Run fmt
+        run: cargo fmt
+      - name: Run Clippy
+        run: cargo clippy --all-targets --all-features
+      - name: Run tests
+        run: cargo test --verbose

README.md

@@ -1,13 +1,54 @@
-Ensure rust is up to date: `rustup update`
-Install the cross toolchain: `rustup target add armv7-unknown-linux-gnueabihf`
-Install cargo-deb: `cargo install cargo-deb`
+# Virtual watchdog for the [OreSat C3](https://github.com/oresat/oresat-c3-hardware)
 
-If it complains about incompatible GLIBC versions consider using an older cross compiler toolchain
-https://github.com/abhiTronix/raspberry-pi-cross-compilers
+The C3 has a radiation tolerant watchdog circuit that will power cycle the whole satellite if it
+hasn't been pet in the last 24 seconds (36s on startup). A "pet" is the rising edge of the GPIO
+line `PET_WDT`. It should be kept high for a reasonable amount of time, at least ~10ms, but both
+the level and falling edge do not reset the timeout. `PET_WDT` is also attached to an LED so having
+a pattern that is pleasing to look at is a plus.
+
+This application provides software configurable interface to the watchdog hardware. Currently the
+two knobs are the initial inhibit time and ongoing reset time. It also provides a UDP interface
+instead of GPIO. This was initially written as a quick-to-start shim that can postpone the watchdog
+while more heavyweight processes (like [oresatd](https://github.com/oresat/oresat-c3-software))
+start which can take a while, at one point it wasn't able to catch the hardware watchdog in time.
+
+```mermaid
+graph TD;
+  A(Inhibit) --> B(Timeout);
+  B --> C;
+  C(Packet) --> B;
+  C --> D(Quit);
+  E(High) --> F(Low);
+  F --> E;
+```
+
+The watchdog listens on UDP localhost:20001 for any packet, which resets the timeout. The contents
+do not matter and are discarded. This currently doesn't do any kind of exclusion or voting which
+is part of more proper software watchdog system, leaving that for programs up the stack.
+
+## Building
+[Install Rust](https://www.rust-lang.org/tools/install) or ensure it is up to date: `rustup update`
+
+Build the program: `cargo b`
+
+### Cross compiling to run on the C3
+The C3 is an ARM system so to run the watchdog in its produciton environment you'll need to install
+the cross toolchain: `rustup target add armv7-unknown-linux-gnueabihf` and add the `--target` flag
+to all cargo commands:
 
-Compile and run the watchdog:
 `cargo r --target armv7-unknown-linux-gnueabihf`
 
-Build a debian package:
+This will also execute `runner.sh`. This script is currently set up to run the watchdog on the
+[flatsat C3](https://github.com/oresat/oresat-flatsat) but you'll need to be connected to the
+OreSat VPN for this to work. This script could alternatively be modified to launch a local VM for
+local testing.
+
+If it complains about incompatible GLIBC versions consider using an older cross compiler toolchain
+[like this one](https://github.com/abhiTronix/raspberry-pi-cross-compilers), and set the linker in
+.cargo/config.toml
+
+### Build a debian package:
+Install cargo-deb: `cargo install cargo-deb`
+Version set in Cargo.toml. If doing a release be sure to also make a tag
 `cargo deb --target armv7-unknown-linux-gnueabihf`
 Package will be in `target/armv7-unknown-linux-gnueabihf/debian/`

runner.sh

@@ -5,7 +5,7 @@ bin=$1
 shift
 
 user="debian" # password: tmppwd
-host="oresat-c3.local"
+host="c3.oresat.org"
 path="pet-wdt"
 
 target="$user@$host"

src/main.rs

@@ -102,8 +102,8 @@ impl Pingee {
         while match self.socket.recv_from(&mut buf) {
             Ok(_) => true,
             Err(e) if e.kind() == ErrorKind::WouldBlock => false,
-            Err(e) => return Err(e).context("Ping socket read failed")
-        } {};
+            Err(e) => return Err(e).context("Ping socket read failed"),
+        } {}
         if let (Some(OneShot(remaining)), OneShot(ping)) = (self.timer.get()?, PING_TIMEOUT) {
             if remaining < ping {
                 self.timer.set(PING_TIMEOUT, TimerSetTimeFlags::empty())?;