first implementation of 1-wire protocol (#505)

onewire: initial implementation for protocol and ds18b20 device

ds18b20/ds18b20.go

@@ -0,0 +1,89 @@
+// Package ds18b20 provides a driver for the DS18B20 digital thermometer
+//
+// Datasheet:
+// https://www.analog.com/media/en/technical-documentation/data-sheets/DS18B20.pdf
+package ds18b20 // import "tinygo.org/x/drivers/ds18b20"
+
+import (
+	"errors"
+)
+
+// Device ROM commands
+const (
+	CONVERT_TEMPERATURE uint8 = 0x44
+	READ_SCRATCHPAD     uint8 = 0xBE
+	WRITE_SCRATCHPAD    uint8 = 0x4E
+)
+
+type OneWireDevice interface {
+	Write(uint8)
+	Read() uint8
+	Select([]uint8) error
+	Сrc8([]uint8, int) uint8
+}
+
+// Device wraps a connection to an 1-Wire devices.
+type Device struct {
+	owd OneWireDevice
+}
+
+// Errors list
+var (
+	errReadTemperature = errors.New("Error: DS18B20. Read temperature error: CRC mismatch.")
+)
+
+func New(owd OneWireDevice) Device {
+	return Device{
+		owd: owd,
+	}
+}
+
+// Configure. Initializes the device, left for compatibility reasons.
+func (d Device) Configure() {}
+
+// ThermometerResolution sets thermometer resolution from 9 to 12 bits
+func (d Device) ThermometerResolution(romid []uint8, resolution uint8) {
+	if 9 <= resolution && resolution <= 12 {
+		d.owd.Select(romid)
+		d.owd.Write(WRITE_SCRATCHPAD)               // send three data bytes to scratchpad (TH, TL, and config)
+		d.owd.Write(0xFF)                           // to TH
+		d.owd.Write(0x00)                           // to TL
+		d.owd.Write(((resolution - 9) << 5) | 0x1F) // to resolution config
+	}
+}
+
+// RequestTemperature sends request to device
+func (d Device) RequestTemperature(romid []uint8) {
+	d.owd.Select(romid)
+	d.owd.Write(CONVERT_TEMPERATURE)
+}
+
+// ReadTemperatureRaw returns the raw temperature.
+// ScratchPad memory map:
+// byte 0: Temperature LSB
+// byte 1: Temperature MSB
+func (d Device) ReadTemperatureRaw(romid []uint8) ([]uint8, error) {
+	spb := make([]uint8, 9) // ScratchPad buffer
+	d.owd.Select(romid)
+	d.owd.Write(READ_SCRATCHPAD)
+	for i := 0; i < 9; i++ {
+		spb[i] = d.owd.Read()
+	}
+	if d.owd.Сrc8(spb, 8) != spb[8] {
+		return nil, errReadTemperature
+	}
+	return spb[:2:2], nil
+}
+
+// ReadTemperature returns the temperature in celsius milli degrees (°C/1000)
+func (d Device) ReadTemperature(romid []uint8) (int32, error) {
+	raw, err := d.ReadTemperatureRaw(romid)
+	if err != nil {
+		return 0, err
+	}
+	t := int32(uint16(raw[0]) | uint16(raw[1])<<8)
+	if t&0x8000 == 0x8000 {
+		t -= 0x10000
+	}
+	return (t * 625 / 10), nil
+}