added generic 8bit shift register (#107)

* shifter: added generic 8bit shift register driver with ShiftPin Pin-compatible GPIO interface

shifter/shifter.go

@@ -0,0 +1,104 @@
+// Package shifter is for 8bit shift register, most common are 74HC165 and 74165
+package shifter // import "tinygo.org/x/drivers/shifter"
+
+import (
+	"errors"
+	"machine"
+)
+
+const (
+	EIGHT_BITS     NumberBit = 8
+	SIXTEEN_BITS   NumberBit = 16
+	THIRTYTWO_BITS NumberBit = 32
+)
+
+type NumberBit int8
+
+// Device holds the Pins.
+type Device struct {
+	latch machine.Pin
+	clk   machine.Pin
+	out   machine.Pin
+	Pins  []ShiftPin
+	bits  NumberBit
+}
+
+// ShiftPin is the implementation of the ShiftPin interface.
+type ShiftPin struct {
+	pin machine.Pin
+	d   *Device
+}
+
+// New returns a new thermistor driver given an ADC pin.
+func New(numBits NumberBit, latch, clk, out machine.Pin) Device {
+	return Device{
+		latch: latch,
+		clk:   clk,
+		out:   out,
+		Pins:  make([]ShiftPin, int(numBits)),
+		bits:  numBits,
+	}
+}
+
+// Configure here just for interface compatibility.
+func (d *Device) Configure() {
+	d.latch.Configure(machine.PinConfig{Mode: machine.PinOutput})
+	d.clk.Configure(machine.PinConfig{Mode: machine.PinOutput})
+	d.out.Configure(machine.PinConfig{Mode: machine.PinInput})
+	for i := 0; i < int(d.bits); i++ {
+		d.Pins[i] = d.GetShiftPin(i)
+	}
+}
+
+// GetShiftPin returns an ShiftPin for a specific input.
+func (d *Device) GetShiftPin(input int) ShiftPin {
+	return ShiftPin{pin: machine.Pin(input), d: d}
+}
+
+// Read8Input reads the 8 inputs and return an uint8
+func (d *Device) Read8Input() (uint8, error) {
+	if d.bits != EIGHT_BITS {
+		return 0, errors.New("wrong amount of registers")
+	}
+	return uint8(d.readInput(EIGHT_BITS)), nil
+}
+
+// Read16Input reads the 16 inputs and return an uint16
+func (d *Device) Read16Input() (uint16, error) {
+	if d.bits != SIXTEEN_BITS {
+		return 0, errors.New("wrong amount of registers")
+	}
+	return uint16(d.readInput(SIXTEEN_BITS)), nil
+}
+
+// Read32Input reads the 32 inputs and return an uint32
+func (d *Device) Read32Input() (uint32, error) {
+	if d.bits != THIRTYTWO_BITS {
+		return 0, errors.New("wrong amount of registers")
+	}
+	return d.readInput(THIRTYTWO_BITS), nil
+}
+
+// Get the current reading for a specific ShiftPin.
+func (p ShiftPin) Get() bool {
+	return (p.d.readInput(p.d.bits) & (1 << int(p.pin))) > 0
+}
+
+// Configure here just for interface compatibility.
+func (p ShiftPin) Configure() {
+}
+
+// readInput reads howMany bits from the shift register
+func (d *Device) readInput(howMany NumberBit) uint32 {
+	d.latch.High()
+	var data uint32
+	for i := howMany - 1; i >= 0; i-- {
+		d.clk.Low()
+		if d.out.Get() {
+			data |= 1 << i
+		}
+		d.clk.High()
+	}
+	d.latch.Low()
+	return data
+}