Add bmp388 support (#219)

bmp388: add support

Makefile

@@ -31,6 +31,8 @@ smoke-test:
 	@md5sum ./build/test.hex
 	tinygo build -size short -o ./build/test.hex -target=itsybitsy-m0 ./examples/bmp280/main.go
 	@md5sum ./build/test.hex
+	tinygo build -size short -o ./build/test.hex -target=trinket-m0 ./examples/bmp388/main.go
+	@md5sum ./build/test.hex
 	tinygo build -size short -o ./build/test.hex -target=bluepill ./examples/ds1307/sram/main.go
 	@md5sum ./build/test.hex
 	tinygo build -size short -o ./build/test.hex -target=bluepill ./examples/ds1307/time/main.go

bmp388/bmp388.go

@@ -0,0 +1,249 @@
+package bmp388
+
+import (
+	"errors"
+
+	"tinygo.org/x/drivers"
+)
+
+var (
+	errConfigWrite  = errors.New("bmp388: failed to configure sensor, check connection")
+	errConfig       = errors.New("bmp388: there is a problem with the configuration, try reducing ODR")
+	errCaliRead     = errors.New("bmp388: failed to read calibration coefficient register")
+	errSoftReset    = errors.New("bmp388: failed to perform a soft reset")
+	errNotConnected = errors.New("bmp388: not connected")
+)
+
+type Oversampling byte
+type Mode byte
+type OutputDataRate byte
+type FilterCoefficient byte
+
+// Config contains settings for filtering, sampling, and modes of operation
+type Config struct {
+	Pressure    Oversampling
+	Temperature Oversampling
+	Mode        Mode
+	ODR         OutputDataRate
+	IIR         FilterCoefficient
+}
+
+// Device wraps the I2C connection and configuration values for the BMP388
+type Device struct {
+	bus     drivers.I2C
+	Address uint8
+	cali    calibrationCoefficients
+	Config  Config
+}
+
+type calibrationCoefficients struct {
+	// Temperature compensation
+	t1 uint16
+	t2 uint16
+	t3 int8
+
+	// Pressure compensation
+	p1  int16
+	p2  int16
+	p3  int8
+	p4  int8
+	p5  uint16
+	p6  uint16
+	p7  int8
+	p8  int8
+	p9  int16
+	p10 int8
+	p11 int8
+}
+
+// New returns a bmp388 struct with the default I2C address. Configure must also be called after instanting
+func New(bus drivers.I2C) Device {
+	return Device{
+		bus:     bus,
+		Address: Address,
+	}
+}
+
+// Configure can enable settings on the BMP388 and reads the calibration coefficients
+func (d *Device) Configure(config Config) (err error) {
+	d.Config = config
+
+	if d.Config == (Config{}) {
+		d.Config.Mode = Normal
+	}
+
+	// Turning on the pressure and temperature sensors and setting the measurement mode
+	err = d.writeRegister(RegPwrCtrl, PwrPress|PwrTemp|byte(d.Config.Mode))
+
+	// Configure the oversampling, output data rate, and iir filter coefficient settings
+	err = d.writeRegister(RegOSR, byte(d.Config.Pressure|d.Config.Temperature<<3))
+	err = d.writeRegister(RegODR, byte(d.Config.ODR))
+	err = d.writeRegister(RegIIR, byte(d.Config.IIR<<1))
+
+	if err != nil {
+		return errConfigWrite
+	}
+
+	// Check if there is a problem with the given configuration
+	if d.configurationError() {
+		return errConfig
+	}
+
+	// Reading the builtin calibration coefficients and parsing them per the datasheet. The compensation formula given
+	// in the datasheet is implemented in floating point
+	buffer, err := d.readRegister(RegCali, 21)
+	if err != nil {
+		return errCaliRead
+	}
+
+	d.cali.t1 = uint16(buffer[1])<<8 | uint16(buffer[0])
+	d.cali.t2 = uint16(buffer[3])<<8 | uint16(buffer[2])
+	d.cali.t3 = int8(buffer[4])
+
+	d.cali.p1 = int16(buffer[6])<<8 | int16(buffer[5])
+	d.cali.p2 = int16(buffer[8])<<8 | int16(buffer[7])
+	d.cali.p3 = int8(buffer[9])
+	d.cali.p4 = int8(buffer[10])
+	d.cali.p5 = uint16(buffer[12])<<8 | uint16(buffer[11])
+	d.cali.p6 = uint16(buffer[14])<<8 | uint16(buffer[13])
+	d.cali.p7 = int8(buffer[15])
+	d.cali.p8 = int8(buffer[16])
+	d.cali.p9 = int16(buffer[18])<<8 | int16(buffer[17])
+	d.cali.p10 = int8(buffer[19])
+	d.cali.p11 = int8(buffer[20])
+
+	return nil
+}
+
+// Read the temperature registers and compute a compensation value for the temperature and pressure compensation
+// calculations. This is not the temperature itself.
+func (d *Device) tlinCompensate() (int64, error) {
+	rawTemp, err := d.readSensorData(RegTemp)
+	if err != nil {
+		return 0, err
+	}
+
+	// pulled from C driver: https://github.com/BoschSensortec/BMP3-Sensor-API/blob/master/bmp3.c
+	partialData1 := rawTemp - (256 * int64(d.cali.t1))
+	partialData2 := int64(d.cali.t2) * partialData1
+	partialData3 := (partialData1 * partialData1)
+	partialData4 := partialData3 * int64(d.cali.t3)
+	partialData5 := (partialData2 * 262144) + partialData4
+	return partialData5 / 4294967296, nil
+
+}
+
+// ReadTemperature returns the temperature in centicelsius, i.e 2426 / 100 = 24.26 C
+func (d *Device) ReadTemperature() (int32, error) {
+
+	tlin, err := d.tlinCompensate()
+	if err != nil {
+		return 0, err
+	}
+
+	temp := (tlin * 25) / 16384
+	return int32(temp), nil
+}
+
+// ReadPressure returns the pressure in centipascals, i.e 10132520 / 100 = 101325.20 Pa
+func (d *Device) ReadPressure() (int32, error) {
+
+	tlin, err := d.tlinCompensate()
+	if err != nil {
+		return 0, err
+	}
+	rawPress, err := d.readSensorData(RegPress)
+	if err != nil {
+		return 0, err
+	}
+
+	// code pulled from bmp388 C driver: https://github.com/BoschSensortec/BMP3-Sensor-API/blob/master/bmp3.c
+	partialData1 := tlin * tlin
+	partialData2 := partialData1 / 64
+	partialData3 := (partialData2 * tlin) / 256
+	partialData4 := (int64(d.cali.p8) * partialData3) / 32
+	partialData5 := (int64(d.cali.p7) * partialData1) * 16
+	partialData6 := (int64(d.cali.p6) * tlin) * 4194304
+	offset := (int64(d.cali.p5) * 140737488355328) + partialData4 + partialData5 + partialData6
+	partialData2 = (int64(d.cali.p4) * partialData3) / 32
+	partialData4 = (int64(d.cali.p3) * partialData1) * 4
+	partialData5 = (int64(d.cali.p2) - 16384) * tlin * 2097152
+	sensitivity := ((int64(d.cali.p1) - 16384) * 70368744177664) + partialData2 + partialData4 + partialData5
+	partialData1 = (sensitivity / 16777216) * rawPress
+	partialData2 = int64(d.cali.p10) * tlin
+	partialData3 = partialData2 + (65536 * int64(d.cali.p9))
+	partialData4 = (partialData3 * rawPress) / 8192
+
+	// dividing by 10 followed by multiplying by 10
+	// To avoid overflow caused by (pressure * partial_data4)
+	partialData5 = (rawPress * (partialData4 / 10)) / 512
+	partialData5 = partialData5 * 10
+	partialData6 = (int64)(uint64(rawPress) * uint64(rawPress))
+	partialData2 = (int64(d.cali.p11) * partialData6) / 65536
+	partialData3 = (partialData2 * rawPress) / 128
+	partialData4 = (offset / 4) + partialData1 + partialData5 + partialData3
+	compPress := ((uint64(partialData4) * 25) / uint64(1099511627776))
+	return int32(compPress), nil
+}
+
+// SoftReset commands the BMP388 to reset of all user configuration settings
+func (d *Device) SoftReset() error {
+	err := d.writeRegister(RegCmd, SoftReset)
+	if err != nil {
+		return errSoftReset
+	}
+	return nil
+}
+
+// Connected tries to reach the bmp388 and check its chip id register. Returns true if it was able to successfully
+// communicate over i2c and returns the correct value
+func (d *Device) Connected() bool {
+	data, err := d.readRegister(RegChipId, 1)
+	return err == nil && data[0] == ChipId // returns true if i2c comm was good and response equals 0x50
+}
+
+// SetMode changes the run mode of the sensor, NORMAL is the one to use for most cases. Use FORCED if you plan to take
+// measurements infrequently and want to conserve power. SLEEP will of course put the sensor to sleep
+func (d *Device) SetMode(mode Mode) error {
+	d.Config.Mode = mode
+	return d.writeRegister(RegPwrCtrl, PwrPress|PwrTemp|byte(d.Config.Mode))
+}
+
+func (d *Device) readSensorData(register byte) (data int64, err error) {
+
+	if !d.Connected() {
+		return 0, errNotConnected
+	}
+
+	// put the sensor back into forced mode to get a reading, the sensor goes back to sleep after taking one read in
+	// forced mode
+	if d.Config.Mode != Normal {
+		err = d.SetMode(Forced)
+		if err != nil {
+			return
+		}
+	}
+
+	bytes, err := d.readRegister(register, 3)
+	if err != nil {
+		return
+	}
+	data = int64(bytes[2])<<16 | int64(bytes[1])<<8 | int64(bytes[0])
+	return
+}
+
+// configurationError checks the register error for the configuration error bit. The bit is cleared on read by the bmp.
+func (d *Device) configurationError() bool {
+	data, err := d.readRegister(RegErr, 1)
+	return err == nil && (data[0]&0x04) != 0
+}
+
+func (d *Device) readRegister(register byte, len int) (data []byte, err error) {
+	data = make([]byte, len)
+	err = d.bus.ReadRegister(d.Address, register, data)
+	return
+}
+
+func (d *Device) writeRegister(register byte, data byte) error {
+	return d.bus.WriteRegister(d.Address, register, []byte{data})
+}

bmp388/registers.go

@@ -0,0 +1,84 @@
+// Package bmp388 provides a driver for Bosch's BMP388 digital temperature & pressure sensor.
+// The datasheet can be found here: https://www.bosch-sensortec.com/media/boschsensortec/downloads/datasheets/bst-bmp388-ds001.pdf
+package bmp388
+
+const Address byte = 0x77 // default I2C address
+
+const (
+	RegChipId  byte = 0x00 // useful for checking the connection
+	RegCali    byte = 0x31 // pressure & temperature compensation calibration coefficients
+	RegPress   byte = 0x04 // start of pressure data registers
+	RegTemp    byte = 0x07 // start of temperature data registers
+	RegPwrCtrl byte = 0x1B // measurement mode & pressure/temperature sensor power register
+	RegOSR     byte = 0x1C // oversampling settings register
+	RegODR     byte = 0x1D //
+	RegCmd     byte = 0x7E // miscellaneous command register
+	RegStat    byte = 0x03 // sensor status register
+	RegErr     byte = 0x02 // error status register
+	RegIIR     byte = 0x1F
+)
+
+const (
+	ChipId    byte = 0x50 // correct response if reading from chip id register
+	PwrPress  byte = 0x01 // power on pressure sensor
+	PwrTemp   byte = 0x02 // power on temperature sensor
+	SoftReset byte = 0xB6 // command to reset all user configuration
+	DRDYPress byte = 0x20 // for checking if pressure data is ready
+	DRDYTemp  byte = 0x40 // for checking if pressure data is ready
+)
+
+// The difference between forced and normal mode is the bmp388 goes to sleep after taking a measurement in forced mode.
+// Set it to forced if you intend to take measurements sporadically and want to save power. The driver will handle
+// waking the sensor up when the sensor is in forced mode.
+const (
+	Normal Mode = 0x30
+	Forced Mode = 0x16
+	Sleep  Mode = 0x00
+)
+
+// Increasing sampling rate increases precision but also the wait time for measurements. The datasheet has a table of
+// suggested values for oversampling, output data rates, and iir filter coefficients by use case.
+const (
+	Sampling1X Oversampling = iota
+	Sampling2X
+	Sampling4X
+	Sampling8X
+	Sampling16X
+	Sampling32X
+)
+
+// Output data rates in Hz. If increasing the sampling rates you need to decrease the output data rates, else the bmp388
+// will freeze and Configure() will return a configuration error message. In that case keep decreasing the data rate
+// until the bmp is happy
+const (
+	Odr200 OutputDataRate = iota
+	Odr100
+	Odr50
+	Odr25
+	Odr12p5
+	Odr6p25
+	Odr3p1
+	Odr1p5
+	Odr0p78
+	Odr0p39
+	Odr0p2
+	Odr0p1
+	Odr0p05
+	Odr0p02
+	Odr0p01
+	Odr0p006
+	Odr0p003
+	Odr0p0015
+)
+
+// IIR filter coefficients, higher values means steadier measurements but slower reaction times
+const (
+	Coeff0 FilterCoefficient = iota
+	Coeff1
+	Coeff3
+	Coeff7
+	Coeff15
+	Coeff31
+	Coeff63
+	Coeff127
+)

examples/bmp388/main.go

@@ -0,0 +1,53 @@
+package main
+
+import (
+	"machine"
+	"strconv"
+	"time"
+
+	"tinygo.org/x/drivers/bmp388"
+)
+
+func main() {
+
+	machine.I2C0.Configure(machine.I2CConfig{})
+
+	sensor := bmp388.New(machine.I2C0)
+	if !sensor.Connected() {
+		println("Uh oh, BMP388 not detected")
+		return
+	}
+
+	// The accuracy of the sensor can be increased, at the cost of a slower output rate. Table 9 in Section 3.5 of the
+	// datasheet has recommended settings for common use cases. If increasing the sampling rate, the output data rate
+	// (ODR) will likely have to be decreased. Configure() will return an error if there's a problem with the
+	// configuration settings - keep decreasing the ODR and cycling the power to the sensor until it is happy.
+	err := sensor.Configure(bmp388.Config{
+		Pressure:    bmp388.Sampling8X,
+		Temperature: bmp388.Sampling2X,
+		ODR:         bmp388.Odr25,
+		IIR:         bmp388.Coeff0,
+		Mode:        bmp388.Normal,
+	})
+
+	// This is also fine
+	// err := sensor.Configure(bmp388.BMP388Config{})
+
+	if err != nil {
+		println(err)
+	}
+
+	for {
+		temp, err := sensor.ReadTemperature() // returns the temperature in centicelsius
+		press, err := sensor.ReadPressure()   // returns the pressure in centipascals
+
+		if err != nil {
+			println(err)
+		} else {
+			println("Temperature: " + strconv.FormatInt(int64(temp), 10) + " cC")
+			println("Pressure:    " + strconv.FormatInt(int64(press), 10) + " cPa\n")
+		}
+
+		time.Sleep(time.Second)
+	}
+}