Crate examples#

Two files, with very different jobs. One is meant to be read and run; the other exists only to be compiled.

four_wheel_minimal.rs — the driver on one screen#

cargo run -p m0601 --example four_wheel_minimal -- /dev/ttyUSB0

Four motors at IDs 1–4 on one RS485 adapter. About 50 lines of actual code, and it touches every part of the multi-motor API in the order you’d meet them:

  1. One shared bus. Bus::open(&port, Duration::from_millis(150))?.with_min_gap(…) — the generous timeout is a backstop for the open; the loop passes its own short reply wait per poll. The idle gap is tightened to 2 ms so the cycle in step 5 fits.
  2. One handle per wheel, sign convention applied once. A const WHEELS: [(u8, bool); 4] table pairs each RS485 id with whether that corner is a mirror-image build, and bus.motor(id)?.mirrored(mirror) bakes it in at construction. After that line the application never touches a sign again — +60 means forward on all four. (Mirroring.)
  3. A stop guard armed before the first frame. A tiny struct StopGuard { bus, ids } whose Drop calls bus.safe_stop_all(&self.ids). Because Bus is Clone it holds its own handle to the same port, and because it’s armed before anything moves, a ? early-return or a panic anywhere below still lands on a bus-wide stop.
  4. A group mode switch. bus.set_mode_all(&ids, Mode::Velocity)?.
  5. The loop, budgeted before it moves. A startup assert! on bus_period(4, 1, bus.min_gap(), REPLY_WAIT) — ~17.2 ms at the 2 ms gap and 2 ms reply wait — checks the traffic fits inside the 20 ms cycle and that the cycle stays at or under drive_floor(). Then: drive all four at 60 RPM, resend every ~20 ms (the 50 Hz floor), and poll one wheel per cycle round-robin — never substituting a query for a drive frame, and never polling all four in one cycle. That is the bus budget advice as working code, right down to the assertion that page recommends.

This is the distilled essence of m0601-quad with the TUI, the logger, and the safety state machine removed, so the driver API is the only thing on screen.

It is safe to build without hardware. With no port argument it prints

usage: four_wheel_minimal <serial-port>   e.g. /dev/ttyUSB0

and returns Ok(()), so cargo build --examples — and CI’s cargo build --workspace --all-targets — never needs a motor.

With a port argument it does spin four wheels at 60 RPM for one second. Clear them first.

usage_doc_check.rs — the compile check behind these docs#

Not meant to be run: its main is empty and every function is #[allow(dead_code)]. Each function mirrors one snippet from the library documentation — query_example, drive_example, transact_example, modes_example, bus_example, multi_motor_example, timing_example, strict_crc_example, position_mirror_example, odometry_example, budgeting_example, slew_example, low_latency_example, mock_example.

The point is that CI builds it (cargo build --workspace --all-targets), so a documented signature that drifts from the real API breaks the build rather than quietly misleading a reader. If you change a public signature, this is the file that will tell you which docs to update.

Keep it in sync when you edit the Library guide — that’s the contract described in Internals.

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