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)
+}

mcp9808/registers.go

@@ -0,0 +1,53 @@
+// 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
+package mcp9808
+
+// Constants/addresses used for I2C.
+const (
+	MCP9808_DEVICE_ID = 0x0400
+	MCP9808_MANUF_ID  = 0x0054
+
+	MCP9808_I2CADDR_DEFAULT = 0x18 //default I2C address
+	MCP9808_REG_CONFIG      = 0x01 //MCP9808 config register
+
+	MCP9808_REG_CONFIG_SHUTDOWN   = 0x0100 //shutdown config
+	MCP9808_REG_CONFIG_CRITLOCKED = 0x0080 //critical trip lock
+	MCP9808_REG_CONFIG_WINLOCKED  = 0x0040 //alarm window lock
+	MCP9808_REG_CONFIG_INTCLR     = 0x0020 //interrupt clear
+	MCP9808_REG_CONFIG_ALERTSTAT  = 0x0010 //alert output status
+	MCP9808_REG_CONFIG_ALERTCTRL  = 0x0008 //alert output control
+	MCP9808_REG_CONFIG_ALERTSEL   = 0x0004 //alert output select
+	MCP9808_REG_CONFIG_ALERTPOL   = 0x0002 //alert output polarity
+	MCP9808_REG_CONFIG_ALERTMODE  = 0x0001 //alert output mode
+
+	MCP9808_REG_UPPER_TEMP   = 0x02 //upper alert boundary
+	MCP9808_REG_LOWER_TEMP   = 0x03 //lower alert boundery
+	MCP9808_REG_CRIT_TEMP    = 0x04 //critical temperature
+	MCP9808_REG_AMBIENT_TEMP = 0x05 //ambient temperature
+	MCP9808_REG_MANUF_ID     = 0x06 //manufacturer ID
+	MCP9808_REG_DEVICE_ID    = 0x07 //device ID
+	MCP9808_REG_RESOLUTION   = 0x08 //resolution
+)
+
+/*
+=======   ============   ==============
+value     resolution     reading Time
+=======   ============   ==============
+
+	0          0.5°C            30 ms
+	1          0.25°C           65 ms
+	2         0.125°C          130 ms
+	3         0.0625°C         250 ms
+
+=======   ============   ==============
+*/
+type resolution uint8
+
+const (
+	Low resolution = iota
+	Medium
+	High
+	Maximum
+)