hd44780: configure and write fixes

- Write only the high-part of the byte when configuring in 4-bit mode
similar to the LiquidCrystal library around
[here](https://github.com/arduino-libraries/LiquidCrystal/blob/1.0.7/src/LiquidCrystal.cpp#L116)

- Pulse enable after writing data
similar to the LiquidCrystal library:
[4-bits here](https://github.com/arduino-libraries/LiquidCrystal/blob/1.0.7/src/LiquidCrystal.cpp#L312),
[8-bits here](https://github.com/arduino-libraries/LiquidCrystal/blob/1.0.7/src/LiquidCrystal.cpp#L320)

Addresses issue [#646](#646).

hd44780/gpio.go

@@ -2,17 +2,26 @@ package hd44780
 
 import (
 	"errors"
+	"time"
 
 	"machine"
 )
 
+type WriteByteType int
+
+const (
+	FullByte   WriteByteType = 3
+	HighNibble WriteByteType = 2
+	LowNibble  WriteByteType = 1
+)
+
 type GPIO struct {
 	dataPins []machine.Pin
 	en       machine.Pin
 	rw       machine.Pin
 	rs       machine.Pin
 
-	write func(data byte)
+	write func(data byte, wt WriteByteType)
 	read  func() byte
 }
 
@@ -48,6 +57,10 @@ func newGPIO(dataPins []machine.Pin, en, rs, rw machine.Pin, mode byte) Device {
 	}
 }
 
+func (g *GPIO) WriteHighNibble(data byte) {
+	g.write(data, HighNibble)
+}
+
 // SetCommandMode sets command/instruction mode
 func (g *GPIO) SetCommandMode(set bool) {
 	if set {
@@ -68,26 +81,36 @@ func (g *GPIO) Write(data []byte) (n int, err error) {
 		g.rw.Low()
 	}
 	for _, d := range data {
-		g.write(d)
+		g.write(d, FullByte)
 		n++
 	}
 	return n, nil
 }
 
-func (g *GPIO) write8BitMode(data byte) {
-	g.en.High()
+func (g *GPIO) write8BitMode(data byte, _ WriteByteType) {
 	g.setPins(data)
-	g.en.Low()
+	g.pulseEnable()
 }
 
-func (g *GPIO) write4BitMode(data byte) {
-	g.en.High()
-	g.setPins(data >> 4)
-	g.en.Low()
+func (g *GPIO) write4BitMode(data byte, wt WriteByteType) {
+	if wt&HighNibble != 0 {
+		g.setPins(data >> 4)
+		g.pulseEnable()
+	}
 
+	if wt&LowNibble != 0 {
+		g.setPins(data)
+		g.pulseEnable()
+	}
+}
+
+func (g *GPIO) pulseEnable() {
+	g.en.Low()
+	time.Sleep(time.Microsecond)
 	g.en.High()
-	g.setPins(data)
+	time.Sleep(time.Microsecond)
 	g.en.Low()
+	time.Sleep(100 * time.Microsecond)
 }
 
 // Read reads len(data) bytes from display RAM to data starting from RAM address counter position

hd44780/hd44780.go

@@ -25,6 +25,7 @@ const (
 
 type Buser interface {
 	io.ReadWriter
+	WriteHighNibble(data byte)
 	SetCommandMode(set bool)
 	WriteOnly() bool
 }
@@ -115,19 +116,17 @@ func (d *Device) Configure(cfg Config) error {
 	time.Sleep(15 * time.Millisecond)
 
 	d.bus.SetCommandMode(true)
-	d.bus.Write([]byte{DATA_LENGTH_8BIT})
+	d.bus.WriteHighNibble(DATA_LENGTH_8BIT)
 	time.Sleep(5 * time.Millisecond)
 
 	for i := 0; i < 2; i++ {
-		d.bus.Write([]byte{DATA_LENGTH_8BIT})
+		d.bus.WriteHighNibble(DATA_LENGTH_8BIT)
 		time.Sleep(150 * time.Microsecond)
-
 	}
 
 	if d.datalength == DATA_LENGTH_4BIT {
-		d.bus.Write([]byte{DATA_LENGTH_4BIT})
+		d.bus.WriteHighNibble(DATA_LENGTH_4BIT)
 	}
-
 	// Busy flag is now accessible
 	d.SendCommand(memoryMap | cfg.Font | d.datalength)
 	d.SendCommand(DISPLAY_OFF)