From f6271cf4a40238b58740bb7aea8b294645835077 Mon Sep 17 00:00:00 2001
From: Falk Scheerschmidt <falk@staffbase.com>
Date: Fri, 10 Dec 2021 11:39:23 +0100
Subject: [PATCH] add sgp30 air quality sensor

---
 sgp30/sgp30.go | 192 +++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 192 insertions(+)
 create mode 100644 sgp30/sgp30.go

diff --git a/sgp30/sgp30.go b/sgp30/sgp30.go
new file mode 100644
index 0000000..e431685
--- /dev/null
+++ b/sgp30/sgp30.go
@@ -0,0 +1,192 @@
+// Copyright 2021 The Periph Authors. All rights reserved.
+// Use of this source code is governed under the Apache License, Version 2.0
+// that can be found in the LICENSE file.
+
+package sgp30
+
+import (
+	"context"
+	"encoding/binary"
+	"errors"
+	"log"
+	"strconv"
+	"sync"
+	"time"
+
+	"periph.io/x/conn/v3"
+	"periph.io/x/conn/v3/i2c"
+)
+
+const (
+	initAirQuality       uint16 = 0x2003
+	measureAirQuality    uint16 = 0x2008
+	getIAQBaseline       uint16 = 0x2015
+	setIAQBaseline       uint16 = 0x201e
+	setHumidity          uint16 = 0x2061
+	measureTest          uint16 = 0x2032
+	getFeatureSetVersion uint16 = 0x202f
+	measureRawSignals    uint16 = 0x2050
+	getTVOCBaseline      uint16 = 0x20b3
+	setTVOCBaseline      uint16 = 0x2077
+
+	i2CAddress uint16 = 0x58
+)
+
+// commandDuration maps the defined maximum measurement duration from the sensor
+var commandDuration = map[uint16]time.Duration{
+	initAirQuality:       time.Millisecond * 10,
+	measureAirQuality:    time.Millisecond * 12,
+	getIAQBaseline:       time.Millisecond * 10,
+	setIAQBaseline:       time.Millisecond * 10,
+	setHumidity:          time.Millisecond * 10,
+	measureTest:          time.Millisecond * 220,
+	getFeatureSetVersion: time.Millisecond * 10,
+	measureRawSignals:    time.Millisecond * 25,
+	getTVOCBaseline:      time.Millisecond * 10,
+	setTVOCBaseline:      time.Millisecond * 10,
+}
+
+// commandResponseLength maps the defined response length including the CRC
+var commandResponseLength = map[uint16]int{
+	measureAirQuality:    6,
+	getIAQBaseline:       6,
+	measureTest:          3,
+	getFeatureSetVersion: 3,
+	measureRawSignals:    6,
+	getTVOCBaseline:      3,
+}
+
+// CO2 represents the current carbon dioxide value in ppm
+type CO2 uint16
+
+func (c CO2) String() string {
+	return strconv.Itoa(int(c)) + "ppm"
+}
+
+func (c *CO2) set(b []byte) {
+	*c = (CO2)(binary.BigEndian.Uint16(b))
+}
+
+// TVOC represents the current total volatile organic compounds value in ppb
+type TVOC uint16
+
+func (t TVOC) String() string {
+	return strconv.Itoa(int(t)) + "ppb"
+}
+
+func (t *TVOC) set(b []byte) {
+	*t = (TVOC)(binary.BigEndian.Uint16(b))
+}
+
+// Env represents measurements from an environmental sensor.
+type Env struct {
+	CO2  CO2
+	TVOC TVOC
+}
+
+// NewI2C returns an object that communicates over I2C to SGP30 environmental sensor.
+//
+// The address must be 0x58.
+func NewI2C(b i2c.Bus, ctx context.Context) (*Dev, error) {
+	d := &Dev{
+		d: &i2c.Dev{Bus: b, Addr: i2CAddress},
+		env: Env{
+			CO2:  400,
+			TVOC: 0,
+		},
+	}
+	if err := d.makeDev(ctx); err != nil {
+		return nil, err
+	}
+	return d, nil
+}
+
+// Dev is a handle to an initialized SGP30 device.
+type Dev struct {
+	d   conn.Conn
+	mu  sync.Mutex
+	env Env
+}
+
+// AirQuality return the value struct for the sensor
+func (d *Dev) AirQuality() Env {
+	d.mu.Lock()
+	defer d.mu.Unlock()
+
+	return d.env
+}
+
+func (d *Dev) makeDev(ctx context.Context) error {
+	// Sending  a "sgp30_iaq_init" command starts the air quality measurement
+	if err := d.initAirQuality(); err != nil {
+		return err
+	}
+
+	// After the "sgp30_iaq_init" command, a "sgp30_measure_iaq" command has to be sent in regular
+	// intervals of 1s to ensure proper operation of the dynamic baseline compensation algorithm.
+	if err := d.measure(); err != nil {
+		log.Print(err)
+	}
+
+	ticker := time.NewTicker(1 * time.Second)
+	go func() {
+		for {
+			select {
+			case <-ticker.C:
+				if err := d.measure(); err != nil {
+					log.Print(err)
+				}
+			case <-ctx.Done():
+				return
+			}
+		}
+	}()
+
+	return nil
+}
+
+func (d *Dev) initAirQuality() error {
+	err := d.writeCommand(initAirQuality)
+	if err == nil {
+		time.Sleep(time.Second * 20)
+	}
+	return err
+}
+
+func (d *Dev) measure() error {
+	buf := make([]byte, commandResponseLength[measureAirQuality])
+	if err := d.readCommand(measureAirQuality, buf); err != nil {
+		return err
+	}
+
+	d.mu.Lock()
+	defer d.mu.Unlock()
+
+	d.env.CO2.set(buf[0:2])
+	d.env.TVOC.set(buf[3:5])
+
+	return nil
+}
+
+func (d *Dev) readCommand(cmd uint16, b []byte) error {
+	if len(b) != commandResponseLength[cmd] {
+		return errors.New("response length mismatch")
+	}
+
+	regAddr := []byte{byte(cmd >> 8), byte(cmd & 0xFF)}
+	if err := d.d.Tx(regAddr, nil); err != nil {
+		return err
+	}
+	time.Sleep(commandDuration[cmd])
+
+	return d.d.Tx(nil, b)
+}
+
+func (d *Dev) writeCommand(cmd uint16) error {
+	regAddr := []byte{byte(cmd >> 8), byte(cmd & 0xFF)}
+	if err := d.d.Tx(regAddr, nil); err != nil {
+		return err
+	}
+	time.Sleep(commandDuration[cmd])
+	return nil
+}