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bme280.go
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bme280.go
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//go:build linux
// Package bme280 implements a bme280 sensor for temperature, humidity, and pressure.
// Code based on https://github.com/sparkfun/SparkFun_bme280_Arduino_Library (MIT license)
// and also https://github.com/rm-hull/bme280 (MIT License)
package bme280
import (
"context"
"encoding/binary"
"errors"
"fmt"
"math"
"time"
"go.viam.com/rdk/components/board/genericlinux/buses"
"go.viam.com/rdk/components/sensor"
"go.viam.com/rdk/logging"
"go.viam.com/rdk/resource"
)
var model = resource.DefaultModelFamily.WithModel("bme280")
const (
defaultI2Caddr = 0x77
// When mode is set to 0, sensors are off.
// When mode is set to 1 or 2, sensors are read once and then turn off again.
// When mode is set to 3, sensors are on and continuously read.
activeMode = 0b11
// Addresses of bme280 registers.
bme280T1LSBReg = 0x88
bme280T1MSBReg = 0x89
bme280T2LSBReg = 0x8A
bme280T2MSBReg = 0x8B
bme280T3LSBReg = 0x8C
bme280T3MSBReg = 0x8D
bme280P1LSBReg = 0x8E
bme280P1MSBReg = 0x8F
bme280P2LSBReg = 0x90
bme280P2MSBReg = 0x91
bme280P3LSBReg = 0x92
bme280P3MSBReg = 0x93
bme280P4LSBReg = 0x94
bme280P4MSBReg = 0x95
bme280P5LSBReg = 0x96
bme280P5MSBReg = 0x97
bme280P6LSBReg = 0x98
bme280P6MSBReg = 0x99
bme280P7LSBReg = 0x9A
bme280P7MSBReg = 0x9B
bme280P8LSBReg = 0x9C
bme280P8MSBReg = 0x9D
bme280P9LSBReg = 0x9E
bme280P9MSBReg = 0x9F
bme280H1Reg = 0xA1
bme280CHIPIDReg = 0xD0 // Chip ID
bme280RSTReg = 0xE0 // Softreset Reg
bme280H2LSBReg = 0xE1
bme280H2MSBReg = 0xE2
bme280H3Reg = 0xE3
bme280H4MSBReg = 0xE4
bme280H4LSBReg = 0xE5
bme280H5MSBReg = 0xE6
bme280H6Reg = 0xE7
bme280CTRLHumidityReg = 0xF2 // Ctrl Humidity Reg
bme280STATReg = 0xF3 // Status Reg
bme280CTRLMEASReg = 0xF4 // Ctrl Measure Reg
bme280ConfigReg = 0xF5 // Configuration Reg
bme280MeasurementsReg = 0xF7 // Measurements register start
bme280PressureMSBReg = 0xF7 // Pressure MSB
bme280PressureLSBReg = 0xF8 // Pressure LSB
bme280PressureXLSBReg = 0xF9 // Pressure XLSB
bme280TemperatureMSBReg = 0xFA // Temperature MSB
bme280TemperatureLSBReg = 0xFB // Temperature LSB
bme280TemperatureXLSBReg = 0xFC // Temperature XLSB
bme280HumidityMSBReg = 0xFD // Humidity MSB
bme280HumidityLSBReg = 0xFE // Humidity LSB
)
// Config is used for converting config attributes.
type Config struct {
// The I2C bus is almost certainly numeric (e.g., the "7" in /dev/i2c-7), but it is nonetheless
// possible for the OS to give its I2C buses a non-numeric identifier, so we store it as a
// string.
I2CBus string `json:"i2c_bus"`
I2cAddr int `json:"i2c_addr,omitempty"`
}
// Validate ensures all parts of the config are valid.
func (conf *Config) Validate(path string) ([]string, error) {
var deps []string
if len(conf.I2CBus) == 0 {
return nil, resource.NewConfigValidationFieldRequiredError(path, "i2c bus")
}
return deps, nil
}
func init() {
resource.RegisterComponent(
sensor.API,
model,
resource.Registration[sensor.Sensor, *Config]{
Constructor: func(
ctx context.Context,
deps resource.Dependencies,
conf resource.Config,
logger logging.Logger,
) (sensor.Sensor, error) {
newConf, err := resource.NativeConfig[*Config](conf)
if err != nil {
return nil, err
}
return newSensor(ctx, deps, conf.ResourceName(), newConf, logger)
},
})
}
func newSensor(
ctx context.Context,
_ resource.Dependencies,
name resource.Name,
conf *Config,
logger logging.Logger,
) (sensor.Sensor, error) {
i2cbus, err := buses.NewI2cBus(conf.I2CBus)
if err != nil {
return nil, fmt.Errorf("bme280 init: failed to open i2c bus %s: %w",
conf.I2CBus, err)
}
addr := conf.I2cAddr
if addr == 0 {
addr = defaultI2Caddr
logger.CWarn(ctx, "using i2c address : 0x77")
}
s := &bme280{
Named: name.AsNamed(),
logger: logger,
bus: i2cbus,
addr: byte(addr),
lastTemp: -999, // initialize to impossible temp
}
err = s.reset(ctx)
if err != nil {
return nil, err
}
// After sending the reset signal above, it takes the chip a short time to be ready to receive commands again
time.Sleep(100 * time.Millisecond)
s.calibration = map[string]int{}
err = s.setupCalibration(ctx)
if err != nil {
return nil, err
}
err = s.setMode(ctx, activeMode)
if err != nil {
return nil, err
}
err = s.setStandbyTime(ctx, 0)
if err != nil {
return nil, err
}
err = s.setFilter(ctx, 0)
if err != nil {
return nil, err
}
// Oversample means "read the sensor this many times and average the results". 1 is generally fine.
// Chip inits to 0 for all, which means "do not read this sensor"/
// humidity
err = s.setOverSample(ctx, bme280CTRLHumidityReg, 0, 1) // Default of 1x oversample
if err != nil {
return nil, err
}
// pressure
err = s.setOverSample(ctx, bme280CTRLMEASReg, 2, 1) // Default of 1x oversample
if err != nil {
return nil, err
}
// temperature
err = s.setOverSample(ctx, bme280CTRLMEASReg, 5, 1) // Default of 1x oversample
if err != nil {
return nil, err
}
return s, nil
}
// bme280 is a i2c sensor device.
type bme280 struct {
resource.Named
resource.AlwaysRebuild
resource.TriviallyCloseable
logger logging.Logger
bus buses.I2C
addr byte
calibration map[string]int
lastTemp float64 // Store raw data from temp for humidity calculations
}
// Readings returns a list containing single item (current temperature).
func (s *bme280) Readings(ctx context.Context, extra map[string]interface{}) (map[string]interface{}, error) {
handle, err := s.bus.OpenHandle(s.addr)
if err != nil {
s.logger.CErrorf(ctx, "can't open bme280 i2c %s", err)
return nil, err
}
err = handle.Write(ctx, []byte{byte(bme280MeasurementsReg)})
if err != nil {
s.logger.CDebug(ctx, "Failed to request temperature")
}
buffer, err := handle.Read(ctx, 8)
if err != nil {
return nil, err
}
if len(buffer) != 8 {
return nil, errors.New("i2c read did not get 8 bytes")
}
pressure := s.readPressure(buffer)
temp := s.readTemperatureCelsius(buffer)
humid := s.readHumidity(buffer)
dewPt := s.calculateDewPoint(temp, humid)
return map[string]interface{}{
"temperature_celsius": temp,
"dew_point_celsius": dewPt,
"temperature_fahrenheit": temp*1.8 + 32,
"dew_point_fahrenheit": dewPt*1.8 + 32,
"relative_humidity_pct": humid,
"pressure_mpa": pressure,
}, handle.Close()
}
// readPressure returns current pressure in mPa.
func (s *bme280) readPressure(buffer []byte) float64 {
adc := float64((int(buffer[0])<<16 | int(buffer[1])<<8 | int(buffer[2])) >> 4)
// Need temp to calculate humidity
if s.lastTemp == -999 {
s.readTemperatureCelsius(buffer)
}
v1 := s.lastTemp/2. - 64000.
v2 := v1 * v1 * float64(s.calibration["digP6"]) / 32768.0
v2 += v1 * float64(s.calibration["digP5"]) * 2.
v2 = v2/4. + float64(s.calibration["digP4"])*65536.
v1 = (float64(s.calibration["digP3"])*v1*v1/524288.0 + float64(s.calibration["digP2"])*v1) / 524288.0
v1 = (1.0 + v1/32768.0) * float64(s.calibration["digP1"])
if v1 == 0 {
return 0
}
res := 1048576.0 - adc
res = ((res - v2/4096.0) * 6250.0) / v1
v1 = float64(s.calibration["digP9"]) * res * res / 2147483648.0
v2 = res * float64(s.calibration["digP8"]) / 32768.0
res += (v1 + v2 + float64(s.calibration["digP7"])) / 16.0
return res / 100.
}
// readTemperatureCelsius returns current temperature in celsius.
func (s *bme280) readTemperatureCelsius(buffer []byte) float64 {
adc := float64((int(buffer[3])<<16 | int(buffer[4])<<8 | int(buffer[5])) >> 4)
var1 := (adc/16382 - float64(s.calibration["digT1"])/1024) * float64(s.calibration["digT2"])
var2 := math.Pow((adc/131072-float64(s.calibration["digT1"])/8192), 2) * float64(s.calibration["digT3"])
tFine := var1 + var2
s.lastTemp = tFine
output := tFine / 5120.
return output
}
// readHumidity returns current humidity as %RH.
func (s *bme280) readHumidity(buffer []byte) float64 {
adc := float64(int(buffer[6])<<8 | int(buffer[7]))
// Need temp to calculate humidity
if s.lastTemp == -999 {
s.readTemperatureCelsius(buffer)
}
var1 := s.lastTemp - 76800.
var1 = (adc - (float64(s.calibration["digH4"])*64.0 + float64(s.calibration["digH5"])/16384.0*var1)) *
(float64(s.calibration["digH2"]) / 65536.0 * (1.0 + float64(s.calibration["digH6"])/67108864.0*var1*(1.0+
float64(s.calibration["digH3"])/67108864.0*var1)))
var1 *= (1.0 - (float64(s.calibration["digH1"]) * var1 / 524288.0))
return math.Max(0., math.Min(var1, 100.))
}
// calculateDewPoint returns current dew point in degrees C.
func (s *bme280) calculateDewPoint(temp, humid float64) float64 {
ratio := 373.15 / (273.15 + temp)
rhs := -7.90298 * (ratio - 1)
rhs += 5.02808 * math.Log10(ratio)
rhs += -1.3816e-7 * (math.Pow(10, (11.344*(1-1/ratio))) - 1)
rhs += 8.1328e-3 * (math.Pow(10, (-3.49149*(ratio-1))) - 1)
rhs += math.Log10(1013.246)
// factor -3 is to adjust units - Vapor Pressure SVP * humidity
vp := math.Pow(10, rhs-3) * humid
// (2) DEWPOINT = F(Vapor Pressure)
t := math.Log(vp / 0.61078) // temp var
denominator := 17.558 - t
if denominator == 0 {
// should be impossible
return 999
}
return (241.88 * t) / denominator
}
func (s *bme280) reset(ctx context.Context) error {
handle, err := s.bus.OpenHandle(s.addr)
if err != nil {
return err
}
err = handle.WriteByteData(ctx, bme280RSTReg, 0xB6)
if err != nil {
return err
}
return handle.Close()
}
// Mode 00 = Sleep
// 01 and 10 = Forced
// 11 = Normal mode.
func (s *bme280) setMode(ctx context.Context, mode int) error {
if mode > activeMode {
mode = 0 // Error check. Default to sleep mode
}
handle, err := s.bus.OpenHandle(s.addr)
if err != nil {
return err
}
controlDataByte, err := handle.ReadByteData(ctx, bme280CTRLMEASReg)
if err != nil {
return err
}
controlData := int(controlDataByte)
controlData |= mode // Set
err = handle.WriteByteData(ctx, bme280CTRLMEASReg, byte(controlData))
if err != nil {
return err
}
return handle.Close()
}
func (s *bme280) currentMode(ctx context.Context) (int, error) {
handle, err := s.bus.OpenHandle(s.addr)
if err != nil {
return -1, err
}
controlDataByte, err := handle.ReadByteData(ctx, bme280CTRLMEASReg)
if err != nil {
return -1, err
}
return (int(controlDataByte) & 0b00000011), handle.Close()
}
func (s *bme280) IsMeasuring(ctx context.Context) (bool, error) {
handle, err := s.bus.OpenHandle(s.addr)
if err != nil {
return false, err
}
stat, err := handle.ReadByteData(ctx, bme280STATReg)
if err != nil {
return false, err
}
return stat&(1<<3) == 1, handle.Close()
}
func (s *bme280) setStandbyTime(ctx context.Context, val byte) error {
handle, err := s.bus.OpenHandle(s.addr)
if err != nil {
return err
}
if val > 0b111 {
val = 0
}
controlData, err := handle.ReadByteData(ctx, bme280ConfigReg)
if err != nil {
return err
}
controlData &= ^((byte(1) << 7) | (byte(1) << 6) | (byte(1) << 5))
controlData |= (val << 5)
err = handle.WriteByteData(ctx, bme280ConfigReg, controlData)
if err != nil {
return err
}
return handle.Close()
}
func (s *bme280) setFilter(ctx context.Context, val byte) error {
handle, err := s.bus.OpenHandle(s.addr)
if err != nil {
return err
}
if val > 0b111 {
val = 0
}
controlData, err := handle.ReadByteData(ctx, bme280ConfigReg)
if err != nil {
return err
}
controlData &= ^((byte(1) << 4) | (byte(1) << 3) | (byte(1) << 2))
controlData |= (val << 2)
err = handle.WriteByteData(ctx, bme280ConfigReg, controlData)
if err != nil {
return err
}
return handle.Close()
}
func (s *bme280) setOverSample(ctx context.Context, addr, offset, val byte) error {
mode, err := s.currentMode(ctx)
if err != nil {
return err
}
if err = s.setMode(ctx, 0b00); err != nil {
return err
}
handle, err := s.bus.OpenHandle(s.addr)
if err != nil {
return err
}
controlData, err := handle.ReadByteData(ctx, addr)
if err != nil {
return err
}
controlData &= ^((byte(1) << (offset + 2)) | (byte(1) << (offset + 1)) | (byte(1) << offset))
controlData |= (val << offset)
if err = handle.WriteByteData(ctx, addr, controlData); err != nil {
return err
}
if err := handle.Close(); err != nil {
return err
}
if err = s.setMode(ctx, mode); err != nil {
return err
}
return nil
}
// setupCalibration sets up all calibration data for the chip.
func (s *bme280) setupCalibration(ctx context.Context) error {
handle, err := s.bus.OpenHandle(s.addr)
if err != nil {
return err
}
// A helper function to read 2 bytes from the handle and interpret it as a word
readWord := func(register byte) (uint16, error) {
rd, err := handle.ReadBlockData(ctx, register, 2)
if err != nil {
return 0, err
}
return binary.LittleEndian.Uint16(rd), nil
}
// Note, some are signed, others are unsigned
if calib, err := readWord(bme280T1LSBReg); err == nil {
s.calibration["digT1"] = int(calib)
} else {
return err
}
if calib, err := readWord(bme280T2LSBReg); err == nil {
s.calibration["digT2"] = int(int16(calib))
} else {
return err
}
if calib, err := readWord(bme280T3LSBReg); err == nil {
s.calibration["digT3"] = int(int16(calib))
} else {
return err
}
if calib, err := readWord(bme280P1LSBReg); err == nil {
s.calibration["digP1"] = int(calib)
} else {
return err
}
if calib, err := readWord(bme280P2LSBReg); err == nil {
s.calibration["digP2"] = int(int16(calib))
} else {
return err
}
if calib, err := readWord(bme280P3LSBReg); err == nil {
s.calibration["digP3"] = int(int16(calib))
} else {
return err
}
if calib, err := readWord(bme280P4LSBReg); err == nil {
s.calibration["digP4"] = int(int16(calib))
} else {
return err
}
if calib, err := readWord(bme280P5LSBReg); err == nil {
s.calibration["digP5"] = int(int16(calib))
} else {
return err
}
if calib, err := readWord(bme280P6LSBReg); err == nil {
s.calibration["digP6"] = int(int16(calib))
} else {
return err
}
if calib, err := readWord(bme280P7LSBReg); err == nil {
s.calibration["digP7"] = int(int16(calib))
} else {
return err
}
if calib, err := readWord(bme280P8LSBReg); err == nil {
s.calibration["digP8"] = int(int16(calib))
} else {
return err
}
if calib, err := readWord(bme280P9LSBReg); err == nil {
s.calibration["digP9"] = int(int16(calib))
} else {
return err
}
calib, err := handle.ReadByteData(ctx, bme280H1Reg)
if err != nil {
return err
}
s.calibration["digH1"] = int(calib)
if calib, err := readWord(bme280H2LSBReg); err == nil {
s.calibration["digH2"] = int(int16(calib))
} else {
return err
}
calib, err = handle.ReadByteData(ctx, bme280H3Reg)
if err != nil {
return err
}
s.calibration["digH3"] = int(calib)
calib, err = handle.ReadByteData(ctx, bme280H6Reg)
if err != nil {
return err
}
s.calibration["digH6"] = int(calib)
r1byte, err := handle.ReadByteData(ctx, bme280H4MSBReg)
if err != nil {
return err
}
r2byte, err := handle.ReadByteData(ctx, bme280H4LSBReg)
if err != nil {
return err
}
s.calibration["digH4"] = (int(r1byte) << 4) + int(r2byte&0x0f)
r1byte, err = handle.ReadByteData(ctx, bme280H5MSBReg)
if err != nil {
return err
}
r2byte, err = handle.ReadByteData(ctx, bme280H4LSBReg)
if err != nil {
return err
}
s.calibration["digH5"] = (int(r1byte) << 4) + int((r2byte>>4)&0x0f)
return handle.Close()
}