pcf8523: RTC driver

pcf8523/pcf8523.go

@@ -0,0 +1,89 @@
+// Package pcf8523 implements a driver for the PCF8523 CMOS Real-Time Clock (RTC)
+//
+// Datasheet: https://www.nxp.com/docs/en/data-sheet/PCF8523.pdf
+package pcf8523
+
+import (
+	"time"
+	"tinygo.org/x/drivers"
+)
+
+type Device struct {
+	bus     drivers.I2C
+	Address uint8
+}
+
+func New(i2c drivers.I2C) Device {
+	return Device{
+		bus:     i2c,
+		Address: DefaultAddress,
+	}
+}
+
+// Reset resets the device according to the datasheet section 8.3
+// This does not wipe the time registers, but resets control registers.
+func (d *Device) Reset() (err error) {
+	return d.bus.Tx(uint16(d.Address), []byte{rControl1, 0x58}, nil)
+}
+
+// SetPowerManagement configures how the device makes use of the backup battery, see
+// datasheet section 8.5
+func (d *Device) SetPowerManagement(b PowerManagement) error {
+	return d.setRegister(rControl3, byte(b)<<5, 0xE0)
+}
+
+func (d *Device) setRegister(reg uint8, value, mask uint8) error {
+	var buf [1]byte
+	err := d.bus.Tx(uint16(d.Address), []byte{reg}, buf[:])
+	if err != nil {
+		return err
+	}
+	buf[0] = (value & mask) | (buf[0] & (^mask))
+	return d.bus.Tx(uint16(d.Address), []byte{reg, buf[0]}, nil)
+}
+
+// SetTime sets the time and date
+func (d *Device) SetTime(t time.Time) error {
+	buf := []byte{
+		rSeconds,
+		bin2bcd(t.Second()),
+		bin2bcd(t.Minute()),
+		bin2bcd(t.Hour()),
+		bin2bcd(t.Day()),
+		bin2bcd(int(t.Weekday())),
+		bin2bcd(int(t.Month())),
+		bin2bcd(t.Year() - 2000),
+	}
+
+	return d.bus.Tx(uint16(d.Address), buf, nil)
+}
+
+// ReadTime returns the date and time
+func (d *Device) ReadTime() (time.Time, error) {
+	buf := make([]byte, 9)
+	err := d.bus.Tx(uint16(d.Address), []byte{rSeconds}, buf)
+	if err != nil {
+		return time.Time{}, err
+	}
+
+	seconds := bcd2bin(buf[0] & 0x7F)
+	minute := bcd2bin(buf[1] & 0x7F)
+	hour := bcd2bin(buf[2] & 0x3F)
+	day := bcd2bin(buf[3] & 0x3F)
+	//skipping weekday buf[4]
+	month := time.Month(bcd2bin(buf[5] & 0x1F))
+	year := int(bcd2bin(buf[6])) + 2000
+
+	t := time.Date(year, month, day, hour, minute, seconds, 0, time.UTC)
+	return t, nil
+}
+
+// bin2bcd converts binary to BCD
+func bin2bcd(dec int) uint8 {
+	return uint8(dec + 6*(dec/10))
+}
+
+// bcd2bin converts BCD to binary
+func bcd2bin(bcd uint8) int {
+	return int(bcd - 6*(bcd>>4))
+}