Feature Flags¶

Cargo features are compile-time switches. They can include optional dependencies, select alternate hardware behavior, or add diagnostics to a firmware image.

Features belong to individual Cargo packages. Specify the package when enabling a feature:

cargo build -p pixracerpro --target thumbv7em-none-eabihf --bin veloxity --release \
  --features 'usb-vcp-serial'

Core Features¶

These features are declared in crates/veloxity_core/Cargo.toml. Board packages may expose matching features that enable the corresponding core feature.

Feature	Purpose	Normal flight build?
`scope-timing-pins`	Disables the core's default full-control test-pin pulse so a board can use its test pins for targeted timing instrumentation. The board must provide the physical pin behavior.	No; measurement-only.
`pre-control-scope`	Pulses test pin 3 while the IMU sample is read, processed, and checked before the control pipeline runs.	No; measurement-only.
`rc-command-scope`	Reserved for RC command/state timing. The current core code does not emit a timing pulse for this feature.	No; currently unimplemented.
`control-scope-estimator`	Pulses test pin 3 while the estimator runs.	No; measurement-only.
`control-scope-controller`	Pulses test pin 3 while the controller runs.	No; measurement-only.
`control-scope-mixer`	Pulses test pin 3 while the mixer runs.	No; measurement-only.
`control-scope-pwm`	Pulses test pin 3 while PWM outputs are configured, composed, and written.	No; measurement-only.

Enable at most one control-scope-* feature at a time. The core rejects builds that select more than one because all four features use the same test pin. These features are useful only on a board that implements the corresponding test-pin output.

Pixracer Pro Features¶

These features are declared in boards/pixracerpro/Cargo.toml.

Feature	Purpose	Normal flight build?
`usb-vcp-serial`	Uses USB virtual COM port (VCP) instead of the companion-computer UART for MAVLink receive and transmit.	No; optional transport.
`scope-timing-pins`	Leaves the Pixracer Pro test pins available for targeted timing instrumentation and disables their built-in indicator pulses. It does not assign a permanent meaning to those pins by itself.	No; measurement-only.
`sensor-poll-diagnostics`	Records sensor-poll success and error counters that can be inspected with a debugger, and periodically logs SBUS receiver diagnostics.	No; diagnostic-only.

The standard Pixracer Pro flash command builds an optimized firmware image with UART MAVLink and no optional features:

cargo xtask flash-board pixracerpro

Use the matching flash options to enable individual features:

cargo xtask flash-board pixracerpro --vcp
cargo xtask flash-board pixracerpro --scope-timing-pins
cargo xtask flash-board pixracerpro --sensor-poll-diagnostics

The options can be combined when more than one behavior is needed:

cargo xtask flash-board pixracerpro --vcp --sensor-poll-diagnostics

The Nucleo-H753ZI package does not currently declare any board-specific Cargo features.

Why Features Matter¶

Feature flags change the compiled firmware image. When reporting a test or timing result, record the exact feature set, target, optimization mode, and board. A diagnostic build is not identical to the standard flight build.