bmi160: add initial support

bmi160/bmi160.go

@@ -0,0 +1,201 @@
+package bmi160
+
+import "machine"
+
+import "time"
+
+// DeviceSPI is the SPI interface to a BMI160 accelerometer/gyroscope. There is
+// also an I2C interface, but it is not yet supported.
+type DeviceSPI struct {
+	// Chip select pin
+	CSB machine.Pin
+
+	// SPI bus (requires chip select to be usable).
+	Bus machine.SPI
+}
+
+// NewSPI returns a new device driver. The pin and SPI interface are not
+// touched, provide a fully configured SPI object and call Configure to start
+// using this device.
+func NewSPI(csb machine.Pin, spi machine.SPI) *DeviceSPI {
+	return &DeviceSPI{
+		CSB: csb, // chip select
+		Bus: spi,
+	}
+}
+
+// Configure configures the BMI160 for use. It configures the CSB pin and
+// configures the BMI160, but it does not configure the SPI interface (it is
+// assumed to be up and running).
+func (d *DeviceSPI) Configure() error {
+	d.CSB.Configure(machine.PinConfig{Mode: machine.PinOutput})
+	d.CSB.High()
+
+	// The datasheet recommends doing a register read from address 0x7F to get
+	// SPI communication going:
+	// > If CSB sees a rising edge after power-up, the BMI160 interface switches
+	// > to SPI until a reset or the next power-up occurs. Therefore, a CSB
+	// > rising edge is needed before starting the SPI communication. Hence, it
+	// > is recommended to perform a SPI single read access to the ADDRESS 0x7F
+	// > before the actual communication in order to use the SPI interface.
+	d.readRegister(0x7F)
+
+	// Power up the accelerometer. 0b0001_00nn is the command format, with 0b01
+	// indicating normal mode.
+	d.runCommand(0b0001_0001)
+
+	// Power up the gyroscope. 0b0001_01nn is the command format, with 0b01
+	// indicating normal mode.
+	d.runCommand(0b0001_0101)
+
+	// Wait until the device is fully initialized. Even after the command has
+	// finished, the gyroscope may not be fully powered on. Therefore, wait
+	// until we get an expected value.
+	// This takes 30ms or so.
+	for {
+		// Wait for the acc_pmu_status and gyr_pmu_status to both be 0b01.
+		if d.readRegister(reg_PMU_STATUS) == 0b0001_0100 {
+			break
+		}
+	}
+
+	return nil
+}
+
+// Connected check whether the device appears to be properly connected. It reads
+// the CHIPID, which must be 0xD1 for the BMI160.
+func (d *DeviceSPI) Connected() bool {
+	return d.readRegister(reg_CHIPID) == 0xD1
+}
+
+// Reset restores the device to the state after power up. This can be useful to
+// easily disable the accelerometer and gyroscope to reduce current consumption.
+func (d *DeviceSPI) Reset() error {
+	d.runCommand(0xB6) // softreset
+	return nil
+}
+
+// ReadTemperature returns the temperature in celsius milli degrees (°C/1000).
+func (d *DeviceSPI) ReadTemperature() (temperature int32, err error) {
+	data := []byte{0x80 | reg_TEMPERATURE_0, 0, 0}
+	d.CSB.Low()
+	err = d.Bus.Tx(data, data)
+	d.CSB.High()
+	if err != nil {
+		return
+	}
+	rawTemperature := int16(uint16(data[1]) | uint16(data[2])<<8)
+	// 0x0000 is 23°C
+	// 0x7fff is ~87°C
+	// We use 0x8000 instead of 0x7fff to make the formula easier. The result
+	// should be near identical and shouldn't affect the result too much (the
+	// temperature sensor has an offset of around 2°C so isn't very reliable).
+	// So the formula is as follows:
+	// 1. Scale from 0x0000..0x8000 to 0..(87-23).
+	//    rawTemperature * (87-23) / 0x8000
+	// 2. Convert to centidegrees.
+	//    rawTemperature * 1000 * (87-23) / 0x8000
+	// 3. Add 23°C offset.
+	//    rawTemperature * 1000 * (87-23) / 0x8000 + 23000
+	// 4. Simplify.
+	//    rawTemperature * 1000 * 64 / 0x8000 + 23000
+	//    rawTemperature * 64000 / 0x8000 + 23000
+	//    rawTemperature * 125 / 64 + 23000
+	temperature = int32(rawTemperature)*125/64 + 23000
+	return
+}
+
+// ReadAcceleration reads the current acceleration from the device and returns
+// it in µg (micro-gravity). When one of the axes is pointing straight to Earth
+// and the sensor is not moving the returned value will be around 1000000 or
+// -1000000.
+func (d *DeviceSPI) ReadAcceleration() (x int32, y int32, z int32, err error) {
+	data := []byte{0x80 | reg_ACC_XL, 0, 0, 0, 0, 0, 0}
+	d.CSB.Low()
+	err = d.Bus.Tx(data, data)
+	d.CSB.High()
+	if err != nil {
+		return
+	}
+	// Now do two things:
+	// 1. merge the two values to a 16-bit number (and cast to a 32-bit integer)
+	// 2. scale the value to bring it in the -1000000..1000000 range.
+	//    This is done with a trick. What we do here is essentially multiply by
+	//    1000000 and divide by 16384 to get the original scale, but to avoid
+	//    overflow we do it at 1/64 of the value:
+	//      1000000 / 64 = 15625
+	//      16384   / 64 = 256
+	x = int32(int16(uint16(data[1])|uint16(data[2])<<8)) * 15625 / 256
+	y = int32(int16(uint16(data[3])|uint16(data[4])<<8)) * 15625 / 256
+	z = int32(int16(uint16(data[5])|uint16(data[6])<<8)) * 15625 / 256
+	return
+}
+
+// ReadRotation reads the current rotation from the device and returns it in
+// µ°/s (micro-degrees/sec). This means that if you were to do a complete
+// rotation along one axis and while doing so integrate all values over time,
+// you would get a value close to 360000000.
+func (d *DeviceSPI) ReadRotation() (x int32, y int32, z int32, err error) {
+	data := []byte{0x80 | reg_GYR_XL, 0, 0, 0, 0, 0, 0}
+	d.CSB.Low()
+	err = d.Bus.Tx(data, data)
+	d.CSB.High()
+	if err != nil {
+		return
+	}
+	// First the value is converted from a pair of bytes to a signed 16-bit
+	// value and then to a signed 32-bit value to avoid integer overflow.
+	// Then the value is scaled to µ°/s (micro-degrees per second).
+	// The default is 2000°/s full scale range for -32768..32767.
+	// The formula works as follows (taking X as an example):
+	// 1. Scale from 32768 to 2000. This means that it is in °/s units.
+	//    rawX * 2000 / 32768
+	// 2. Scale to µ°/s by multiplying by 1e6.
+	//    rawX * 1e6 * 2000 / 32768
+	// 3. Simplify.
+	//    rawX * 2e9 / 32768
+	//    rawX * 1953125 / 32
+	rawX := int32(int16(uint16(data[1]) | uint16(data[2])<<8))
+	rawY := int32(int16(uint16(data[3]) | uint16(data[4])<<8))
+	rawZ := int32(int16(uint16(data[5]) | uint16(data[6])<<8))
+	x = int32(int64(rawX) * 1953125 / 32)
+	y = int32(int64(rawY) * 1953125 / 32)
+	z = int32(int64(rawZ) * 1953125 / 32)
+	return
+}
+
+// runCommand runs a BMI160 command through the CMD register. It waits for the
+// command to complete before returning.
+func (d *DeviceSPI) runCommand(command uint8) {
+	d.writeRegister(reg_CMD, command)
+	for {
+		response := d.readRegister(reg_CMD)
+		if response == 0 {
+			return // command was completed
+		}
+	}
+}
+
+// readRegister reads from a single BMI160 register. It should only be used for
+// single register reads, not for reading multiple registers at once.
+func (d *DeviceSPI) readRegister(address uint8) uint8 {
+	// I don't know why but it appears necessary to sleep for a bit here.
+	time.Sleep(time.Millisecond)
+
+	data := []byte{0x80 | address, 0}
+	d.CSB.Low()
+	d.Bus.Tx(data, data)
+	d.CSB.High()
+	return data[1]
+}
+
+// writeRegister writes a single byte BMI160 register. It should only be used
+// for writing to a single register.
+func (d *DeviceSPI) writeRegister(address, data uint8) {
+	// I don't know why but it appears necessary to sleep for a bit here.
+	time.Sleep(time.Millisecond)
+
+	d.CSB.Low()
+	d.Bus.Tx([]byte{address, data}, []byte{0, 0})
+	d.CSB.High()
+}

bmi160/registers.go

@@ -0,0 +1,44 @@
+package bmi160
+
+const (
+	reg_CHIPID        = 0x00
+	reg_ERR_REG       = 0x02
+	reg_PMU_STATUS    = 0x03
+	reg_MAG_XL        = 0x04
+	reg_MAG_XH        = 0x05
+	reg_MAG_YL        = 0x06
+	reg_MAG_YH        = 0x07
+	reg_MAG_ZL        = 0x08
+	reg_MAG_ZH        = 0x09
+	reg_RHALL_L       = 0x0A
+	reg_RHALL_H       = 0x0B
+	reg_GYR_XL        = 0x0C
+	reg_GYR_XH        = 0x0D
+	reg_GYR_YL        = 0x0E
+	reg_GYR_YH        = 0x0F
+	reg_GYR_ZL        = 0x10
+	reg_GYR_ZH        = 0x11
+	reg_ACC_XL        = 0x12
+	reg_ACC_XH        = 0x13
+	reg_ACC_YL        = 0x14
+	reg_ACC_YH        = 0x15
+	reg_ACC_ZL        = 0x16
+	reg_ACC_ZH        = 0x17
+	reg_SENSORTIME_0  = 0x18
+	reg_SENSORTIME_1  = 0x19
+	reg_SENSORTIME_2  = 0x1A
+	reg_STATUS        = 0x1B
+	reg_INT_STATUS_0  = 0x1C
+	reg_INT_STATUS_1  = 0x1D
+	reg_INT_STATUS_2  = 0x1E
+	reg_INT_STATUS_3  = 0x1F
+	reg_TEMPERATURE_0 = 0x20
+	reg_TEMPERATURE_1 = 0x21
+	reg_FIFO_LENGTH_0 = 0x22
+	reg_FIFO_LENGTH_1 = 0x23
+	reg_FIFO_DATA     = 0x24
+
+	// ...
+
+	reg_CMD = 0x7E
+)