devices: Add support for AM2320 Temperature/Humidity Sensor (#82)

* AM2320 Temp/Humidity Sensor - Initial Add

am2320/am2320.go

@@ -0,0 +1,181 @@
+// Copyright 2024 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.
+
+// This package provides a driver for the AOSONG AM2320 Temperature/Humidity
+// Sensor. This sensor is a basic, inexpensive i2c sensor with reasonably good
+// accuracy for both temperature and humidity.
+//
+// # Datasheet
+//
+// https://cdn-shop.adafruit.com/product-files/3721/AM2320.pdf
+package am2320
+
+import (
+	"errors"
+	"fmt"
+	"sync"
+	"time"
+
+	"periph.io/x/conn/v3"
+	"periph.io/x/conn/v3/i2c"
+	"periph.io/x/conn/v3/physic"
+)
+
+// Dev represents an am2320 temperature/humidity sensor.
+type Dev struct {
+	d        *i2c.Dev
+	mu       sync.Mutex
+	shutdown chan struct{}
+}
+
+const (
+	// The address of this device is fixed. Note that the datasheet states
+	// the value is 0xb8, which is incorrect.
+	SensorAddress uint16 = 0x5c
+
+	humidityRegisters byte = 0x00
+)
+
+// Create a new am2320 device and return it.
+func NewI2C(b i2c.Bus, addr uint16) (*Dev, error) {
+	d := &Dev{d: &i2c.Dev{Bus: b, Addr: addr}}
+	return d, nil
+}
+
+// Halt interrupts a running SenseContinuous() operation.
+func (dev *Dev) Halt() error {
+	dev.mu.Lock()
+	defer dev.mu.Unlock()
+	if dev.shutdown != nil {
+		close(dev.shutdown)
+	}
+	return nil
+}
+
+// Algorithm from the datasheet. Returns true if CRC matches check value.
+func checkCRC(bytes []byte) bool {
+	crc := uint16(0xffff)
+	for ix := range len(bytes) - 2 {
+		b := uint16(bytes[ix])
+		crc ^= b
+		for range 8 {
+			if (crc & 0x01) == 0x01 {
+				crc = crc >> 1
+				crc ^= 0xa001
+			} else {
+				crc = crc >> 1
+			}
+		}
+	}
+	chk := uint16(bytes[len(bytes)-2]) | uint16(bytes[len(bytes)-1])<<8
+	return chk == crc
+}
+
+// readCommand provides the logic of communicating with the sensor. According
+// to the datasheet, it tries to stay in low-power as much as possible to
+// avoid self-heating the sensors. This makes it finicky to talk to. On success,
+// returns a slice of registerCount bytes starting from registerAddress.
+func (dev *Dev) readCommand(registerAddress, registerCount byte) ([]byte, error) {
+	// Send a wake-up call to the device.
+	var err error
+	for range 5 {
+		err = dev.d.Tx([]byte{0}, nil)
+		if err == nil {
+			break
+		}
+		time.Sleep(100 * time.Millisecond)
+	}
+	w := []byte{0x3, registerAddress, registerCount}
+	// The read return format is:
+	//
+	// {operation,registerCount,requested registers...,crc low, crc high}
+	r := make([]byte, registerCount+4)
+
+	for range 10 {
+		err = dev.d.Tx(w, r)
+		if err == nil &&
+			w[0] == r[0] && w[2] == r[1] &&
+			checkCRC(r) {
+
+			return r[2 : 2+registerCount], nil
+		}
+		time.Sleep(2 * time.Second)
+	}
+	if err == nil {
+		err = errors.New("invalid return values or crc from sensor")
+	}
+	return nil, fmt.Errorf("am2320 error sending read command: %w", err)
+}
+
+// Sense queries the sensor for the current temperature and humidity. Note that
+// the sensor reports a sample rate of 1/2 hz. It's recommended to not poll
+// the sensor more frequently than once every 3 seconds.
+func (dev *Dev) Sense(env *physic.Env) error {
+	env.Temperature = 0
+	env.Pressure = 0
+	env.Humidity = 0
+
+	dev.mu.Lock()
+	defer dev.mu.Unlock()
+
+	r, err := dev.readCommand(humidityRegisters, 4)
+	if err != nil {
+		return err
+	}
+
+	h := int16(r[0])<<8 | int16(r[1])
+	env.Humidity = physic.RelativeHumidity(h) * physic.MilliRH
+	t := int16(r[2])<<8 | int16(r[3])
+	env.Temperature = physic.ZeroCelsius + (physic.Celsius/10)*physic.Temperature(t)
+
+	return nil
+}
+
+// SenseContinuous returns a channel that can be read to return values from
+// the sensor. The minimum value for interval is 3 seconds. To end the read,
+// call Halt()
+func (dev *Dev) SenseContinuous(interval time.Duration) (<-chan physic.Env, error) {
+	if interval < (3 * time.Second) {
+		return nil, errors.New("am2320: invalid duration. minimum 3 seconds")
+	}
+	if dev.shutdown != nil {
+		return nil, errors.New("am2320: sense continuous already running")
+	}
+
+	dev.shutdown = make(chan struct{})
+	ch := make(chan physic.Env, 16)
+	go func() {
+		ticker := time.NewTicker(interval)
+		defer ticker.Stop()
+		for {
+			select {
+			case <-dev.shutdown:
+				close(ch)
+				dev.shutdown = nil
+				return
+			case <-ticker.C:
+				e := physic.Env{}
+				err := dev.Sense(&e)
+				if err == nil {
+					ch <- e
+				}
+			}
+		}
+	}()
+	return ch, nil
+}
+
+func (dev *Dev) String() string {
+	return fmt.Sprintf("am2320: %s", dev.d)
+}
+
+// Precision returns the resolution of the device for it's measured parameters.
+func (dev *Dev) Precision(env *physic.Env) {
+	env.Temperature = physic.Celsius / 10
+	env.Pressure = 0
+	env.Humidity = physic.MilliRH
+}
+
+var _ conn.Resource = &Dev{}
+var _ physic.SenseEnv = &Dev{}

am2320/am2320_test.go

@@ -0,0 +1,190 @@
+// Copyright 2024 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 am2320
+
+import (
+	"fmt"
+	"os"
+	"testing"
+	"time"
+
+	"periph.io/x/conn/v3/i2c"
+	"periph.io/x/conn/v3/i2c/i2creg"
+	"periph.io/x/conn/v3/i2c/i2ctest"
+	"periph.io/x/conn/v3/physic"
+	"periph.io/x/host/v3"
+)
+
+var bus i2c.Bus
+var liveDevice bool
+
+// Playback values for a single sense operation.
+var pbSense = []i2ctest.IO{
+	{Addr: SensorAddress, W: []uint8{0x0}},
+	{Addr: SensorAddress, W: []uint8{0x3, 0x0, 0x4}, R: []uint8{0x3, 0x4, 0x1, 0x5c, 0x0, 0xef, 0x71, 0x8a}}}
+
+func init() {
+	var err error
+
+	liveDevice = os.Getenv("AM2320") != ""
+
+	// Make sure periph is initialized.
+	if _, err = host.Init(); err != nil {
+		fmt.Println(err)
+	}
+
+	if liveDevice {
+		bus, err = i2creg.Open("")
+		if err != nil {
+			fmt.Println(err)
+		}
+		// Add the recorder to dump the data stream when we're using a live device.
+		bus = &i2ctest.Record{Bus: bus}
+	} else {
+		bus = &i2ctest.Playback{DontPanic: true}
+	}
+
+}
+
+// getDev returns a configured device using either an i2c bus, or a playback bus.
+func getDev(t *testing.T, playbackOps ...[]i2ctest.IO) (*Dev, error) {
+	if liveDevice {
+		if recorder, ok := bus.(*i2ctest.Record); ok {
+			// Clear the operations buffer.
+			recorder.Ops = make([]i2ctest.IO, 0, 32)
+		}
+	} else {
+		if len(playbackOps) == 1 {
+			pb := bus.(*i2ctest.Playback)
+			pb.Ops = playbackOps[0]
+			pb.Count = 0
+		}
+	}
+	dev, err := NewI2C(bus, SensorAddress)
+
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	return dev, err
+}
+
+// shutdown dumps the recorder values if we we're running a live device.
+func shutdown(t *testing.T) {
+	if recorder, ok := bus.(*i2ctest.Record); ok {
+		t.Logf("%#v", recorder.Ops)
+	}
+}
+
+func TestBasic(t *testing.T) {
+	dev := Dev{}
+	env := &physic.Env{}
+	dev.Precision(env)
+	if env.Pressure != 0 {
+		t.Error("this device doesn't measure pressure")
+	}
+	if 10*env.Temperature != physic.Celsius {
+		t.Error("incorrect temperature precision value")
+	}
+	if env.Humidity != physic.MilliRH {
+		t.Error("incorrect humidity precision")
+	}
+
+	s := dev.String()
+	if len(s) == 0 {
+		t.Error("invalid value for String()")
+	}
+
+	// Check the CRC Calculation algorithm using the data supplied by the vendor.
+	crcTest := []byte{0x03, 0x04, 0x01, 0xf4, 0x00, 0xfa, 0x31, 0xa5}
+	if !checkCRC(crcTest) {
+		t.Error("crc error")
+	}
+	// ensure a corruption is detected.
+	crcTest[0] = crcTest[0] ^ 0xff
+	if checkCRC(crcTest) {
+		t.Error("crc error")
+	}
+}
+
+func TestSense(t *testing.T) {
+	d, err := getDev(t, pbSense)
+	if err != nil {
+		t.Fatalf("failed to initialize am2320: %v", err)
+	}
+	defer shutdown(t)
+
+	// Read temperature and humidity from the sensor
+	e := physic.Env{}
+
+	if err := d.Sense(&e); err != nil {
+		t.Fatal(err)
+	}
+	t.Logf("%8s %9s", e.Temperature, e.Humidity)
+
+	if !liveDevice {
+		// The playback temp is 23.9C Ensure that's what we got.
+		expected := physic.ZeroCelsius + 23_900*physic.MilliKelvin
+		if e.Temperature != expected {
+			t.Errorf("incorrect temperature value read. Expected: %s (%d) Found: %s (%d)",
+				e.Temperature.String(),
+				e.Temperature,
+				expected.String(),
+				expected)
+		}
+
+		// 34.8% expected.
+		expectedRH := 34*physic.PercentRH + 8*physic.MilliRH
+		if e.Humidity != expectedRH {
+			t.Errorf("incorrect humidity value read. Expected: %s (%d) Found: %s (%d)",
+				e.Humidity.String(),
+				e.Humidity,
+				expectedRH.String(),
+				expectedRH)
+		}
+	}
+}
+
+func TestSenseContinuous(t *testing.T) {
+	readCount := 10
+
+	// make 10 copies of the single reading playback data.
+	pb := make([]i2ctest.IO, 0, len(pbSense)*10)
+	for range readCount {
+		pb = append(pb, pbSense...)
+	}
+
+	d, err := getDev(t, pb)
+	if err != nil {
+		t.Fatalf("failed to initialize am2320: %v", err)
+	}
+	defer shutdown(t)
+
+	_, err = d.SenseContinuous(time.Second)
+	if err == nil {
+		t.Error("SenseContinuous() accepted invalid reading interval")
+	}
+	ch, err := d.SenseContinuous(3 * time.Second)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	go func() {
+		time.Sleep(3 * time.Duration(readCount) * time.Second)
+		err := d.Halt()
+		if err != nil {
+			t.Error(err)
+		}
+	}()
+
+	count := 0
+	for e := range ch {
+		count += 1
+		t.Log(time.Now(), e)
+	}
+	if count < (readCount-1) || count > (readCount+1) {
+		t.Errorf("expected %d readings. received %d", readCount, count)
+	}
+}