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Virtual watchdog for the OreSat C3

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) start which can take a while, at one point it wasn't able to catch the hardware watchdog in time.

graph TD;
  A(Inhibit) --> B(Timeout);
  B --> C;
  C(Packet) --> B;
  C --> D(Quit);
  E(High) --> F(Low);
  F --> E;
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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 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:

cargo r --target armv7-unknown-linux-gnueabihf

To have cargo run the application on the flatsat C3 add the card="c3" cfg option:

RUSTFLAGS='--cfg card="c3"' cargo r --target armv7-unknown-linux-gnueabihf

This will execute .cargo/runner.sh which is set up to run the watchdog on the 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 running it complains about incompatible GLIBC versions consider using an older cross compiler toolchain like this one, and set the linker in .cargo/config.toml:

[target.armv7-unknown-linux-gnueabihf]
linker = ".cargo/cross-pi-gcc-10.3.0-2/bin/arm-linux-gnueabihf-gcc"

Build a debian package

Install cargo-deb: cargo install cargo-deb. The version is 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/

Debugging

  • Omit the --release flag to run in debug mode
  • Prints petted and pinged times

cargo run

  • use the -- sim flag to create a simulated gpiochip during runtime

cargo run -- sim

  • Handy script that will ping the watchdog UDP port every 5 seconds

tests/test_ping.sh

Testing the watchdog

cargo test

cargo test -- --nocapture for print statements in the test functions