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fchiesadoc
100 lines
4.1 KiB
Go
100 lines
4.1 KiB
Go
// Package mpu9150 provides a driver for the MPU9150 accelerometer and gyroscope
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// made by InvenSense.
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//
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// Datasheets:
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// https://invensense.tdk.com/wp-content/uploads/2015/02/MPU-9150-Datasheet.pdf
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// https://inertialelements.com/documents/resources_page/MPU9150-register-manual.pdf
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package mpu9150
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import (
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"tinygo.org/x/drivers"
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"tinygo.org/x/drivers/internal/legacy"
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)
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// Device wraps an I2C connection to a MPU9150 device.
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type Device struct {
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bus drivers.I2C
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Address uint16
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}
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// New creates a new MPU9150 connection. The I2C bus must already be
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// configured.
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//
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// This function only creates the Device object, it does not touch the device.
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func New(bus drivers.I2C) Device {
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return Device{bus, Address}
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}
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// Connected returns whether a MPU9150 has been found.
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// It does a "who am I" request and checks the response.
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func (d Device) Connected() bool {
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data := []byte{0}
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legacy.ReadRegister(d.bus, uint8(d.Address), WHO_AM_I, data)
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return data[0] == 0x68 // 4.32 Register 117 – Who Am I (MPU-9150 Register Map and Descriptions)
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}
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// Configure sets up the device for communication.
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func (d Device) Configure() error {
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return d.SetClockSource(CLOCK_INTERNAL)
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}
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// ReadAcceleration reads the current acceleration from the device and returns
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// it in µg (micro-gravity). When one of the axes is pointing straight to Earth
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// and the sensor is not moving the returned value will be around 1000000 or
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// -1000000.
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func (d Device) ReadAcceleration(accel_axis byte) (x int32, y int32, z int32) {
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data := make([]byte, 6)
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legacy.ReadRegister(d.bus, uint8(d.Address), accel_axis, data)
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// Now do two things:
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// 1. merge the two values to a 16-bit number (and cast to a 32-bit integer)
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// 2. scale the value to bring it in the -1000000..1000000 range.
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// This is done with a trick. What we do here is essentially multiply by
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// 1000000 and divide by 16384 to get the original scale, but to avoid
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// overflow we do it at 1/64 of the value:
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// 1000000 / 64 = 15625
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// 16384 / 64 = 256
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x = int32(int16((uint16(data[0])<<8)|uint16(data[1]))) * 15625 / 256
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y = int32(int16((uint16(data[2])<<8)|uint16(data[3]))) * 15625 / 256
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z = int32(int16((uint16(data[4])<<8)|uint16(data[5]))) * 15625 / 256
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return
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}
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// ReadRotation reads the current rotation from the device and returns it in
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// µ°/s (micro-degrees/sec). This means that if you were to do a complete
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// rotation along one axis and while doing so integrate all values over time,
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// you would get a value close to 360000000.
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func (d Device) ReadRotation(gyro_axis byte) (x int32, y int32, z int32) {
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data := make([]byte, 6)
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legacy.ReadRegister(d.bus, uint8(d.Address), gyro_axis, data)
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// First the value is converted from a pair of bytes to a signed 16-bit
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// value and then to a signed 32-bit value to avoid integer overflow.
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// Then the value is scaled to µ°/s (micro-degrees per second).
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// This is done in the following steps:
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// 1. Multiply by 250 * 1000_000
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// 2. Divide by 32768
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// The following calculation (x * 15625 / 2048 * 1000) is essentially the
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// same but avoids overflow. First both operations are divided by 16 leading
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// to multiply by 15625000 and divide by 2048, and then part of the multiply
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// is done after the divide instead of before.
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x = int32(int16((uint16(data[0])<<8)|uint16(data[1]))) * 15625 / 2048 * 1000
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y = int32(int16((uint16(data[2])<<8)|uint16(data[3]))) * 15625 / 2048 * 1000
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z = int32(int16((uint16(data[4])<<8)|uint16(data[5]))) * 15625 / 2048 * 1000
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return
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}
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// SetClockSource allows the user to configure the clock source.
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func (d Device) SetClockSource(source uint8) error {
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return legacy.WriteRegister(d.bus, uint8(d.Address), PWR_MGMT_1, []uint8{source})
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}
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// SetFullScaleGyroRange allows the user to configure the scale range for the gyroscope.
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func (d Device) SetFullScaleGyroRange(rng uint8) error {
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return legacy.WriteRegister(d.bus, uint8(d.Address), GYRO_CONFIG, []uint8{rng})
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}
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// SetFullScaleAccelRange allows the user to configure the scale range for the accelerometer.
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func (d Device) SetFullScaleAccelRange(rng uint8) error {
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return legacy.WriteRegister(d.bus, uint8(d.Address), ACCEL_CONFIG, []uint8{rng})
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}
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