Introduces driver for Sensirion SHT-4X Temperature/Humidity Sensors. (#109)

Move CRC8 logic into common package for resuability.

Author: gsexton

common/crc.go

@@ -0,0 +1,24 @@
+// Copyright 2025 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 common contains functions used across multiple packages. For
+// example, a CRC8 calculation
+package common
+
+// CRC8 calculates the 8-bit CRC of the byte slice parameter and returns the
+// calculated value. CRC bytes are used in sensors from TI and Sensirion.
+func CRC8(bytes []byte) byte {
+	var crc byte = 0xff
+	for _, val := range bytes {
+		crc ^= val
+		for range 8 {
+			if (crc & 0x80) == 0 {
+				crc <<= 1
+			} else {
+				crc = (byte)((crc << 1) ^ 0x31)
+			}
+		}
+	}
+	return crc
+}

common/crc_test.go

@@ -0,0 +1,24 @@
+// Copyright 2025 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 common
+
+import "testing"
+
+func TestCRC8(t *testing.T) {
+	var tests = []struct {
+		bytes  []byte
+		result byte
+	}{
+		{bytes: []byte{0xbe, 0xef}, result: 0x92},
+		{bytes: []byte{0x01, 0xa4}, result: 0x4d},
+		{bytes: []byte{0xab, 0xcd}, result: 0x6f},
+	}
+	for _, test := range tests {
+		res := CRC8(test.bytes)
+		if res != test.result {
+			t.Errorf("CRC8(%#v)!=0x%d received 0x%d", test.bytes, test.result, res)
+		}
+	}
+}

hdc302x/hdc302x.go

@@ -21,6 +21,7 @@ import (
 	"periph.io/x/conn/v3"
 	"periph.io/x/conn/v3/i2c"
 	"periph.io/x/conn/v3/physic"
+	"periph.io/x/devices/v3/common"
 )
 
 type SampleRate uint16
@@ -203,21 +204,6 @@ func countToHumidity(bytes []byte) physic.RelativeHumidity {
 	return physic.RelativeHumidity(f * float64(physic.PercentRH))
 }
 
-func crc8(bytes []byte) byte {
-	var crc byte = 0xff
-	for _, val := range bytes {
-		crc ^= val
-		for range 8 {
-			if (crc & 0x80) == 0 {
-				crc <<= 1
-			} else {
-				crc = (byte)((crc << 1) ^ 0x31)
-			}
-		}
-	}
-	return crc
-}
-
 // Halt shuts down the device. If a SenseContinuous operation is in progress,
 // its aborted. Implements conn.Resource
 func (dev *Dev) Halt() error {
@@ -251,7 +237,7 @@ func (dev *Dev) Sense(env *physic.Env) error {
 	if err := dev.d.Tx(read, res); err != nil {
 		return fmt.Errorf("hdc302x: %w", err)
 	}
-	if crc8(res[:2]) != res[2] || crc8(res[3:5]) != res[5] {
+	if common.CRC8(res[:2]) != res[2] || common.CRC8(res[3:5]) != res[5] {
 		return errInvalidCRC
 	}
 	env.Temperature = countToTemperature(res)
@@ -320,7 +306,7 @@ func (dev *Dev) readSerialNumber() int64 {
 	// this is a 6 byte value read in 3 parts
 	for range 3 {
 		err := dev.d.Tx(cmd, r)
-		if err != nil || (crc8(r[:2]) != r[2]) {
+		if err != nil || (common.CRC8(r[:2]) != r[2]) {
 			return result
 		}
 		result = result<<16 | (int64(r[0])<<8 | int64(r[1]))
@@ -358,7 +344,7 @@ func (dev *Dev) readAlertValues(cfg *Configuration) error {
 		if err != nil {
 			return err
 		}
-		if crc8(r[:2]) != r[2] {
+		if common.CRC8(r[:2]) != r[2] {
 			return errInvalidCRC
 		}
 		wValue := uint16(r[0])<<8 | uint16(r[1])
@@ -381,7 +367,7 @@ func (dev *Dev) readOffsets(cfg *Configuration) error {
 	if err := dev.d.Tx(readSetOffsets, r); err != nil {
 		return fmt.Errorf("hdc302x: %w", err)
 	}
-	if crc8(r[:2]) != r[2] {
+	if common.CRC8(r[:2]) != r[2] {
 		return errInvalidCRC
 	}
 
@@ -424,7 +410,7 @@ func (dev *Dev) ReadStatus() (StatusWord, error) {
 	if err := dev.d.Tx(readStatus, r); err != nil {
 		return 0, err
 	}
-	if crc8(r[:2]) != r[2] {
+	if common.CRC8(r[:2]) != r[2] {
 		return 0, errInvalidCRC
 	}
 	_ = dev.d.Tx(clearStatus, nil)
@@ -463,7 +449,7 @@ func (dev *Dev) setOffsets(cfg *Configuration) error {
 		computeTemperatureOffsetByte(cfg.TemperatureOffset),
 		0,
 	}
-	w[4] = crc8(w[2:4])
+	w[4] = common.CRC8(w[2:4])
 	return dev.d.Tx(w, nil)
 }
 
@@ -553,7 +539,7 @@ func (dev *Dev) setThresholds(typeAlert bool, tp *ThresholdPair) error {
 		wval := uint16(0)
 		wval = (humBits & 0xfe00) | tempBits>>7
 		w := []byte{cmds[pair][ix][0], cmds[pair][ix][1], byte(wval >> 8), byte(wval & 0xff), 0}
-		w[4] = crc8(w[2:4])
+		w[4] = common.CRC8(w[2:4])
 		err := dev.d.Tx(w, nil)
 		if err != nil {
 			return err
@@ -609,7 +595,7 @@ func (dev *Dev) SetHeater(powerLevel HeaterPower) error {
 		byte((powerLevel >> 8) & 0xff),
 		byte(powerLevel & 0xff),
 		0}
-	setValue[4] = crc8(setValue[2:4])
+	setValue[4] = common.CRC8(setValue[2:4])
 	err := dev.d.Tx(setValue, nil)
 	if err != nil {
 		return err

hdc302x/hdc302x_test.go

@@ -200,22 +200,6 @@ func shutdown(t *testing.T) {
 	}
 }
 
-func TestCRC(t *testing.T) {
-	var tests = []struct {
-		bytes  []byte
-		result byte
-	}{
-		{bytes: []byte{0xbe, 0xef}, result: 0x92},
-		{bytes: []byte{0xab, 0xcd}, result: 0x6f},
-	}
-	for _, test := range tests {
-		res := crc8(test.bytes)
-		if res != test.result {
-			t.Errorf("crc8(%#v)!=0x%d receieved 0x%d", test.bytes, test.result, res)
-		}
-	}
-}
-
 // TestConversions tests the various temperature/humidity functions
 // for correct operation.
 func TestConversions(t *testing.T) {

scd4x/scd4x.go

@@ -12,6 +12,7 @@ import (
 
 	"periph.io/x/conn/v3/i2c"
 	"periph.io/x/conn/v3/physic"
+	"periph.io/x/devices/v3/common"
 )
 
 // PPM=Parts Per Million. Units of measure for CO2 concentration.
@@ -402,30 +403,14 @@ func (d *Dev) Reset(mode ResetMode) error {
 	return err
 }
 
-func calcCRC(bytes []byte) byte {
-	polynomial := byte(0x31)
-	crc := byte(0xff)
-	for ix := range len(bytes) {
-		crc ^= bytes[ix]
-		for crc_bit := byte(8); crc_bit > 0; crc_bit-- {
-			if (crc & 0x80) == 0x80 {
-				crc = (crc << 1) ^ polynomial
-			} else {
-				crc = (crc << 1)
-			}
-		}
-	}
-	return crc
-}
-
 // makeWriteData converts the slice of word values into byte values with the
 // CRC following.
 func makeWriteData(data []uint16) []byte {
 	bytes := make([]byte, len(data)*3)
 	for ix, val := range data {
 		bytes[ix*3] = byte((val >> 8) & 0xff)
 		bytes[ix*3+1] = byte(val & 0xff)
-		bytes[ix*3+2] = calcCRC(bytes[ix*3 : ix*3+2])
+		bytes[ix*3+2] = common.CRC8(bytes[ix*3 : ix*3+2])
 	}
 	return bytes
 }
@@ -464,7 +449,7 @@ func (d *Dev) sendCommand(cmd command, writeData []uint16) ([]uint16, error) {
 	// verify the CRC as we go.
 	result := make([]uint16, cmd.responseSize/3)
 	for ix := range len(result) {
-		crc := calcCRC(r[ix*3 : ix*3+2])
+		crc := common.CRC8(r[ix*3 : ix*3+2])
 		if r[ix*3+2] != crc {
 			return nil, fmt.Errorf("scd4x cmd 0x%x: invalid crc", cmd.cmdWord)
 		}

scd4x/scd4x_test.go

@@ -154,22 +154,6 @@ func shutdown(t *testing.T) {
 	}
 }
 
-func TestCRC(t *testing.T) {
-	tests := []struct {
-		bytes []byte
-		crc   byte
-	}{
-		{bytes: []byte{0xbe, 0xef}, crc: 0x92},
-		{bytes: []byte{0x01, 0xa4}, crc: 0x4d},
-	}
-	for _, test := range tests {
-		res := calcCRC(test.bytes)
-		if res != test.crc {
-			t.Error(fmt.Errorf("crc calculation error bytes: %#v, result: 0x%x expected: 0x%x", test.bytes, res, test.crc))
-		}
-	}
-}
-
 func TestCountToTemperature(t *testing.T) {
 	tests := []struct {
 		count    uint16

sht4x/example_test.go

@@ -0,0 +1,44 @@
+// Copyright 2025 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 sht4x_test
+
+import (
+	"log"
+	"time"
+
+	"periph.io/x/conn/v3/i2c/i2creg"
+	"periph.io/x/conn/v3/physic"
+	"periph.io/x/devices/v3/sht4x"
+	"periph.io/x/host/v3"
+)
+
+// Example shows creating an SHT-4X sensor and reading from it.
+func Example() {
+	if _, err := host.Init(); err != nil {
+		log.Fatal("Error calling host.init()")
+	}
+	bus, err := i2creg.Open("")
+	if err != nil {
+		log.Fatal(err)
+	}
+	defer bus.Close()
+
+	dev, err := sht4x.New(bus, sht4x.DefaultAddress)
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	env := &physic.Env{}
+
+	for range 10 {
+		err = dev.Sense(env)
+		if err != nil {
+			log.Println(err)
+		} else {
+			log.Printf("Temperature: %s   Humidity: %s\n", env.Temperature, env.Humidity)
+		}
+		time.Sleep(time.Second)
+	}
+}