Add driver for MCP9808 i2c temperature sensor (#676)

mcp9808: add support for temperature sensor

mcp9808/mcp9808.go

@@ -0,0 +1,98 @@
+// Package mcp9808 implements a driver for the MCP9808 High Accuracy I2C Temperature Sensor
+//
+// Datasheet: https://cdn-shop.adafruit.com/datasheets/MCP9808.pdf
+// Module: https://www.adafruit.com/product/1782
+// Only implemented: temperature reading, resolution read & set
+package mcp9808
+
+import (
+	"encoding/binary"
+	"errors"
+
+	"tinygo.org/x/drivers"
+)
+
+type Device struct {
+	bus     drivers.I2C
+	Address uint16
+}
+
+func New(bus drivers.I2C) Device {
+	return Device{bus, MCP9808_I2CADDR_DEFAULT}
+}
+
+func (d *Device) Connected() bool {
+	data := make([]byte, 2)
+	d.Read(MCP9808_REG_DEVICE_ID, &data)
+	return binary.BigEndian.Uint16(data) == MCP9808_DEVICE_ID
+}
+
+func (d *Device) ReadTemperature() (float64, error) {
+	data := make([]byte, 2)
+	var temp float64
+	if err := d.Read(MCP9808_REG_AMBIENT_TEMP, &data); err != nil {
+		return 0, err
+	}
+
+	data[0] = data[0] & 0x1F
+	if data[0]&0x10 == 0x10 {
+		data[0] = data[0] & 0x0F
+		temp = float64(data[0])*16 + float64(data[1])/16.0 - 256
+	}
+	temp = float64(data[0])*16 + float64(data[1])/16.0
+	return temp, nil
+}
+
+func (d *Device) ReadResolution() (resolution, error) {
+	data := make([]byte, 2)
+	err := d.Read(MCP9808_REG_RESOLUTION, &data)
+	if err != nil {
+		return 0, err
+	}
+	switch data[0] {
+	case 0:
+		return Low, nil
+	case 1:
+		return Medium, nil
+	case 2:
+		return High, nil
+	case 3:
+		return Maximum, nil
+
+	default:
+		return 0, errors.New("unknown resolution")
+	}
+}
+
+func (d *Device) SetResolution(r resolution) error {
+	switch r {
+	case Low:
+		if err := d.Write(MCP9808_REG_RESOLUTION, []byte{0x00}); err != nil {
+			return err
+		}
+	case Medium:
+		if err := d.Write(MCP9808_REG_RESOLUTION, []byte{0x01}); err != nil {
+			return err
+		}
+	case High:
+		if err := d.Write(MCP9808_REG_RESOLUTION, []byte{0x02}); err != nil {
+			return err
+		}
+	case Maximum:
+		if err := d.Write(MCP9808_REG_RESOLUTION, []byte{0x03}); err != nil {
+			return err
+		}
+	default:
+		return nil
+	}
+	return nil
+}
+
+func (d *Device) Write(register byte, data []byte) error {
+	buf := append([]byte{register}, data...)
+	return d.bus.Tx(d.Address, buf, nil)
+}
+
+func (d *Device) Read(register byte, data *[]byte) error {
+	return d.bus.Tx(d.Address, []byte{register}, *data)
+}