feat: add support for seesaw encoders

Adds the necessary function addresses for reading and writing encoders on a seesaw.
Also provides two helper functions to make this easier.

examples/seesaw/rotary-encoder/main.go

@@ -0,0 +1,35 @@
+package main
+
+import (
+	"machine"
+	"time"
+
+	"tinygo.org/x/drivers/seesaw"
+)
+
+// example reading the position of a rotary encoder (4991) powered by a seesaw
+// https://learn.adafruit.com/adafruit-i2c-qt-rotary-encoder/arduino
+func main() {
+	// This assumes you are using an Adafruit QT Py RP2040 for its Stemma QT connector
+	// https://www.adafruit.com/product/4900
+	i2c := machine.I2C1
+	i2c.Configure(machine.I2CConfig{
+		SCL: machine.I2C1_QT_SCL_PIN,
+		SDA: machine.I2C1_QT_SDA_PIN,
+	})
+
+	dev := seesaw.New(i2c)
+	dev.Address = 0x36
+
+	for {
+		time.Sleep(time.Second)
+
+		pos, err := dev.GetEncoderPosition(0, false)
+		if err != nil {
+			println(err)
+			continue
+		}
+
+		println(pos)
+	}
+}

seesaw/encoder.go

@@ -0,0 +1,49 @@
+package seesaw
+
+import (
+	"errors"
+)
+
+var errInvalidEncoderNumber = errors.New("invalid encoder choice, 0-15 are supported")
+
+// GetEncoderPosition returns the absolute position (or delta since the previous call) of the specified rotary encoder.
+func (d *Device) GetEncoderPosition(encoder uint, asDelta bool) (int32, error) {
+	if encoder >= 16 {
+		return 0, errInvalidEncoderNumber
+	}
+
+	// The function address' upper nibble is the function, the lower nibble selects which encoder to communicate with
+	fnAddr := FunctionAddress(encoder)
+	if asDelta {
+		fnAddr |= FunctionEncoderDelta
+	} else {
+		fnAddr |= FunctionEncoderPosition
+	}
+
+	var buf [4]byte
+	err := d.Read(ModuleEncoderBase, fnAddr, buf[:])
+	if err != nil {
+		return 0, err
+	}
+
+	return int32(buf[0])<<24 | int32(buf[1])<<16 | int32(buf[2])<<8 | int32(buf[3]), nil
+}
+
+// SetEncoderPosition calibrate's the encoder's current absolute position to be whatever the provided position is.
+func (d *Device) SetEncoderPosition(encoder uint, position int32) error {
+	if encoder >= 16 {
+		return errInvalidEncoderNumber
+	}
+
+	// The function address' upper nibble is the function, the lower nibble selects which encoder to communicate with
+	fnAddr := FunctionEncoderPosition | FunctionAddress(encoder)
+
+	buf := [4]byte{
+		byte(position >> 24),
+		byte(position >> 16),
+		byte(position >> 8),
+		byte(position),
+	}
+
+	return d.Write(ModuleEncoderBase, fnAddr, buf[:])
+}

seesaw/registers.go

@@ -98,3 +98,13 @@ const (
 	FunctionKeypadCount    FunctionAddress = 0x04
 	FunctionKeypadFifo     FunctionAddress = 0x10
 )
+
+// encoder module function address registers
+// these are the defaults for encoder 0, change the lower nibble to address other encoders
+// see the Device.GetEncoderPosition and SetEncoderPosition methods for examples.
+const (
+	FunctionEncoderIntenset FunctionAddress = 0x10
+	FunctionEncoderIntenclr FunctionAddress = 0x20
+	FunctionEncoderPosition FunctionAddress = 0x30
+	FunctionEncoderDelta    FunctionAddress = 0x40
+)