BNO055 Driver — PID Fork

Maintained fork of eupn/bno055 for the PID autonomous motor control system. no_std compatible, embedded-hal 1.0.

Why fork?

The upstream crate had:

• Two unsafe blocks in calibration serialization (raw pointer casts) — removed
• A bug where AxisRemap::y() returned the X axis — fixed
• A 900-line monolithic lib.rs — split into 9 modules
• No tests — 206 tests added
• Unit error type on AxisRemapBuilder::build() — replaced with InvalidAxisRemap
• Redundant I2C writes on every sensor read — page tracking added
• No bulk read option — all_sensor_data() added (36% faster full-sensor poll)
• Three unnecessary dependencies (byteorder, num-derive, num-traits) — removed

Hardware setup

Component	Value
Sensor	Bosch BNO055 (9-axis IMU, on-chip sensor fusion)
Host	Raspberry Pi 5
Bus	I2C-1 (/dev/i2c-1)
Address	0x28 (alternate, COM3 pulled LOW)
Datasheet	BST-BNO055-DS000

Module structure

src/
  sensors.rs       318 lines  Sensor reads, bulk read, AllSensorData struct
  lib.rs           204 lines  Struct, Error, init, reset, I2C helpers, re-exports
  axis.rs          191 lines  AxisRemap builder, AxisConfig, AxisSign
  mode.rs          179 lines  OperationMode, PowerMode, RegisterPage
  calibration.rs   176 lines  Calibration struct, status, profile read/write
  acc_config.rs    174 lines  AccConfig types, get/set methods
  status.rs        141 lines  SystemStatus, Revision, SelfTest
  regs.rs          122 lines  Register addresses
  std.rs            18 lines  Display impls (std feature only)

Benchmarks

Measured on Raspberry Pi 5, I2C-1 at 100kHz (standard mode), BNO055 in NDOF fusion mode. Sensor stationary on flat surface. Run with cargo bench --bench sensor_reads.

Before optimizations (upstream baseline)

Read type	I2C bytes	Time	Max throughput
temperature	1	1.02 ms	~980 Hz
calibration_status	1	1.04 ms	~960 Hz
accel_data	6	1.69 ms	~590 Hz
gyro_data	6	1.67 ms	~600 Hz
mag_data	6	1.71 ms	~585 Hz
euler_angles	6	1.70 ms	~588 Hz
linear_acceleration	6	1.70 ms	~588 Hz
gravity	6	1.68 ms	~595 Hz
quaternion	8	1.97 ms	~508 Hz
all 6 sensors (individual)	~33	9.83 ms	~102 Hz
calibration_profile	22 + mode switch	43.9 ms	—
init	reset + configure	653.6 ms	—

Every sensor read wasted an I2C write to set the register page even when already on the correct page. A full sensor loop barely fit in a 10 ms window (100 Hz).

After optimizations (this fork)

Read type	I2C bytes	Time	Improvement
temperature	1	0.60 ms	-41%
calibration_status	1	0.60 ms	-42%
accel_data	6	1.26 ms	-25%
gyro_data	6	1.24 ms	-26%
mag_data	6	1.26 ms	-26%
euler_angles	6	1.24 ms	-27%
linear_acceleration	6	1.26 ms	-26%
gravity	6	1.26 ms	-25%
quaternion	8	1.53 ms	-22%
all 6 sensors (individual)	~33	7.16 ms	-27%
all_sensor_data (bulk)	45	6.28 ms	-36%
calibration_profile	22 + mode switch	42.6 ms	-3%
init	reset + configure	652.0 ms	no change

Full sensor loop: 9.83 ms -> 6.28 ms (~102 Hz -> ~159 Hz).

What was optimized

#	Optimization	Impact	Details
1	Page tracking	-27% on all reads	Added page field to Bno055. set_page() skips the I2C write when already on the correct page. Eliminated ~0.5 ms per read.
2	Bulk sensor read	-36% vs baseline	New all_sensor_data() reads registers 0x08-0x34 (45 bytes) in one I2C transaction instead of 6+ separate reads.
3	Removed byteorder	code quality	Replaced LittleEndian::read_i16() with i16::from_le_bytes() from core. One fewer dependency.
4	Removed num-derive/num-traits	code quality	Replaced FromPrimitive derives with manual match arms. Two fewer proc-macro dependencies.
5	Calibration buffer cleanup	code clarity	Replaced iterator chain with copy_from_slice.

Changes from upstream

Bug fixes

• AxisRemap::y() returned wrong axis — the getter returned self.x instead of self.y, hidden by #[allow(clippy::misnamed_getters)]. Fixed and lint allow removed.

Safety

• Removed both unsafe blocks in BNO055Calibration. from_buf() now constructs field-by-field. as_bytes() now returns an owned [u8; 22] instead of an unsafe &[u8] tied to a raw pointer cast.

Performance

• Page tracking — set_page() tracks the current page and skips the I2C write when the requested page is already active. After soft_reset(), the tracker resets to page 0.
• Bulk sensor read — new all_sensor_data() method reads all sensor registers in one I2C transaction. Returns AllSensorData with Option fields based on mode availability.

API changes

• BNO055Calibration::as_bytes() returns [u8; 22] instead of &[u8].
• AxisRemapBuilder::build() returns Result<AxisRemap, InvalidAxisRemap> instead of Result<AxisRemap, ()>.
• New all_sensor_data() method and AllSensorData struct.

Dependencies removed

• byteorder — replaced with i16::from_le_bytes() / u16::from_le_bytes() from core.
• num-derive — replaced FromPrimitive derive with manual match arms.
• num-traits — no longer needed without FromPrimitive.

Architecture

• lib.rs (996 lines) split into 9 focused modules. No breaking public API change.
• Internal fields and helpers changed from private to pub(crate) to support the split.

Tests

206 integration tests covering:

• Every public API method — happy path and I2C error path
• All 13 operation modes — sensor availability matrix
• Calibration repr(C) struct — byte-by-byte field mapping for all 22 bytes
• AxisRemapBuilder — all swap functions, all invalid states, register encoding
• Sensor scaling — exact conversion factors verified for all sensor types
• Bulk read — value consistency with individual reads, mode-dependent availability
• i16 boundary values, alternative I2C address, page switching, mode transitions
• Debug formatting, consecutive reads, double init

Run with cargo test.

Usage

Individual sensor reads

use bno055::{Bno055, BNO055OperationMode};
use linux_embedded_hal::{Delay, I2cdev};

let i2c = I2cdev::new("/dev/i2c-1").unwrap();
let mut delay = Delay {};
let mut imu = Bno055::new(i2c).with_alternative_address();

imu.init(&mut delay)?;
imu.set_mode(BNO055OperationMode::NDOF, &mut delay)?;

let quat = imu.quaternion()?;
let euler = imu.euler_angles()?;
let accel = imu.accel_data()?;
let gyro = imu.gyro_data()?;
let mag = imu.mag_data()?;
let temp = imu.temperature()?;

Bulk sensor read (recommended for control loops)

// Single I2C transaction — reads all sensors at once.
let data = imu.all_sensor_data()?;

// Fields are Option — None if the current mode doesn't enable that sensor.
if let Some(quat) = data.quaternion {
    // Use quaternion orientation
}
if let Some(accel) = data.accel {
    // Use accelerometer data (m/s^2)
}
let temp = data.temperature; // Always available

Feature flags

Flag	Effect
std	Adds std::error::Error impl for Error type
serde	Adds Serialize/Deserialize for BNO055Calibration
defmt-03	Adds defmt::Format derives for no_std logging

I2C notes

The BNO055 has known I2C clock-stretching issues. If reads fail intermittently:

• Lower I2C bus speed (try 100 kHz standard mode).
• Increase I2C timeout on your host.
• See Adafruit's notes.

The sensor has a 400-650 ms startup delay (datasheet chapter 1.2). If your MCU boots faster than the sensor, delay before calling init() or retry on failure.

License

MIT