Shiftregister implementation (#135)

* Basic support of SIPO shift register

* typo

* add example of shiftregister for arduino and nucleo

* Fix build flag for nucleof103rb

* Fix wrong data pin configuration

* Change README.md for Shift registers

* Add API for individual register's output pin

* Rewrite shift register example to show ShiftPin usage

* Fix target for shiftregister example smoke test

* Fix type in makefile

* Add shiftregister compatble IC

* Edit comment and readme

shiftregister/shiftregister.go

@@ -0,0 +1,93 @@
+// Package shiftregister is for 8bit shift output register using 3 GPIO pins like SN74ALS164A, SN74AHC594, SN74AHC595, ...
+package shiftregister
+
+import (
+	"machine"
+)
+
+type NumberBit int8
+
+// Bit number of the register
+const (
+	EIGHT_BITS     NumberBit = 8
+	SIXTEEN_BITS   NumberBit = 16
+	THIRTYTWO_BITS NumberBit = 32
+)
+
+// Device holds pin number
+type Device struct {
+	latch, clock, out machine.Pin // IC wiring
+	bits              NumberBit   // Pin number
+	mask              uint32      // keep all pins state
+}
+
+// ShiftPin is the implementation of the ShiftPin interface.
+// ShiftPin provide an interface like regular machine.Pin
+type ShiftPin struct {
+	mask uint32  // Bit representing the pin
+	d    *Device // Reference to the register
+}
+
+// New returns a new shift output register device
+func New(Bits NumberBit, Latch, Clock, Out machine.Pin) *Device {
+	return &Device{
+		latch: Latch,
+		clock: Clock,
+		out:   Out,
+		bits:  Bits,
+	}
+}
+
+// Configure set hardware configuration
+func (d *Device) Configure() {
+	d.latch.Configure(machine.PinConfig{Mode: machine.PinOutput})
+	d.clock.Configure(machine.PinConfig{Mode: machine.PinOutput})
+	d.out.Configure(machine.PinConfig{Mode: machine.PinOutput})
+	d.latch.High()
+}
+
+// WriteMask applies mask's bits to register's outputs pin
+// mask's MSB set Q1, LSB set Q8 (for 8 bits mask)
+func (d *Device) WriteMask(mask uint32) {
+	d.mask = mask // Keep the mask for individual addressing
+	d.latch.Low()
+	for i := 0; i < int(d.bits); i++ {
+		d.clock.Low()
+		d.out.Set(mask&1 != 0)
+		mask = mask >> 1
+		d.clock.High()
+	}
+	d.latch.High()
+}
+
+// GetShiftPin return an individually addressable pin
+func (d *Device) GetShiftPin(pin int) *ShiftPin {
+	if pin < 0 || pin > int(d.bits) {
+		panic("invalid pin number")
+	}
+	return &ShiftPin{
+		mask: 1 << pin,
+		d:    d,
+	}
+
+}
+
+// Set changes the value of this register pin.
+func (p ShiftPin) Set(value bool) {
+	d := p.d
+	if value {
+		d.WriteMask(d.mask | p.mask)
+	} else {
+		d.WriteMask(d.mask & ^p.mask)
+	}
+}
+
+// High sets this shift register pin to high.
+func (p ShiftPin) High() {
+	p.Set(true)
+}
+
+// Low sets this shift register pin to low.
+func (p ShiftPin) Low() {
+	p.Set(false)
+}