megapi: use serialport adaptor and move driver to drivers/serial

README.md

@@ -391,6 +391,7 @@ the `gobot/drivers/serial` package:
 - [UART](https://en.wikipedia.org/wiki/Serial_port) <=> [Drivers](https://github.com/hybridgroup/gobot/tree/master/drivers/serial)
   - Sphero: Sphero
   - Neurosky: MindWave
+  - MegaPi: MotorDriver
 
 Support for devices that use Serial Peripheral Interface (SPI) have
 a shared set of drivers provided using the `gobot/drivers/spi` package:

drivers/MIGRATION.md

@@ -115,7 +115,7 @@ import(
 
 ### Neurosky adaptor split off
 
-The Neurosky adaptor now us the generic serial adaptor. The driver part was moved. With this, the imports needs to be
+The Neurosky adaptor now use the generic serial adaptor. The driver part was moved. With this, the imports needs to be
 adjusted. In addition all events now have a suffix "Event", see below.
 
 ```go
@@ -148,6 +148,37 @@ import(
 ...
 ```
 
+### MegaPi adaptor split off
+
+The MegaPi adaptor now use the generic serial adaptor. The driver part was moved. With this, the imports needs to be
+adjusted.
+
+```go
+// old
+import(
+  ...
+  "gobot.io/x/gobot/v2/platforms/megapi"
+  ...
+)
+
+...
+  megaPiAdaptor := megapi.NewAdaptor("/dev/ttyS0")
+  motor := megapi.NewMotorDriver(megaPiAdaptor, 1)
+...
+
+// new
+import(
+  ...
+  "gobot.io/x/gobot/v2/drivers/serial/megapi"
+  "gobot.io/x/gobot/v2/platforms/serialport"
+  ...
+)
+...
+  adaptor := serialport.NewAdaptor("/dev/ttyS0", serialport.WithName("MegaPi"))
+  motor := megapi.NewMotorDriver(adaptor, 1)
+...
+```
+
 ## Switch from version 2.2.0 (gpio drivers affected)
 
 ### gpio.ButtonDriver, gpio.PIRMotionDriver: substitute parameter "v time.duration"

drivers/serial/README.md

@@ -14,3 +14,4 @@ Gobot has a extensible system for connecting to hardware devices. The following
 
 - Sphero: Sphero
 - Neurosky: MindWave
+- MegaPi: MotorDriver

drivers/serial/megapi/motor_driver.go

@@ -0,0 +1,130 @@
+package megapi
+
+import (
+	"bytes"
+	"encoding/binary"
+	"log"
+	"sync"
+	"time"
+
+	"gobot.io/x/gobot/v2"
+	"gobot.io/x/gobot/v2/drivers/serial"
+)
+
+var _ gobot.Driver = (*MotorDriver)(nil)
+
+type megapiMotorSerialAdaptor interface {
+	gobot.Adaptor
+	serial.SerialWriter
+}
+
+// MotorDriver represents a motor
+type MotorDriver struct {
+	*serial.Driver
+	port              byte
+	halted            bool
+	writeBytesChannel chan []byte
+	finalizeChannel   chan struct{}
+	syncRoot          *sync.Mutex
+}
+
+// NewMotorDriver creates a new MotorDriver at the given port
+func NewMotorDriver(a megapiMotorSerialAdaptor, port byte, opts ...serial.OptionApplier) *MotorDriver {
+	d := &MotorDriver{
+		port:              port,
+		halted:            true,
+		syncRoot:          &sync.Mutex{},
+		writeBytesChannel: make(chan []byte),
+		finalizeChannel:   make(chan struct{}),
+	}
+	d.Driver = serial.NewDriver(a, "MegaPiMotor", d.initialize, d.shutdown, opts...)
+
+	return d
+}
+
+// Speed sets the motors speed to the specified value
+func (d *MotorDriver) Speed(speed int16) error {
+	d.syncRoot.Lock()
+	defer d.syncRoot.Unlock()
+
+	if d.halted {
+		return nil
+	}
+	return d.speedHelper(speed)
+}
+
+// initialize implements the Driver interface
+func (d *MotorDriver) initialize() error {
+	d.syncRoot.Lock()
+	defer d.syncRoot.Unlock()
+
+	// sleeping is required to give the board a chance to reset after connection is done
+	time.Sleep(2 * time.Second)
+
+	// kick off thread to send bytes to the board
+	go func() {
+		for {
+			select {
+			case bytes := <-d.writeBytesChannel:
+				if _, err := d.adaptor().SerialWrite(bytes); err != nil {
+					panic(err)
+				}
+				time.Sleep(10 * time.Millisecond)
+			case <-d.finalizeChannel:
+				d.finalizeChannel <- struct{}{}
+				return
+			default:
+				time.Sleep(10 * time.Millisecond)
+			}
+		}
+	}()
+
+	d.halted = false
+	return d.speedHelper(0)
+}
+
+// Halt terminates the Driver interface
+func (d *MotorDriver) shutdown() error {
+	d.syncRoot.Lock()
+	defer d.syncRoot.Unlock()
+
+	d.finalizeChannel <- struct{}{}
+	<-d.finalizeChannel
+
+	d.halted = true
+	return d.speedHelper(0)
+}
+
+// there is some sort of bug on the hardware such that you cannot
+// send the exact same speed to 2 different motors consecutively
+// hence we ensure we always alternate speeds
+func (d *MotorDriver) speedHelper(speed int16) error {
+	if err := d.sendSpeed(speed - 1); err != nil {
+		return err
+	}
+	return d.sendSpeed(speed)
+}
+
+// sendSpeed sets the motors speed to the specified value
+func (d *MotorDriver) sendSpeed(speed int16) error {
+	bufOut := new(bytes.Buffer)
+
+	// byte sequence: 0xff, 0x55, id, action, device, port
+	bufOut.Write([]byte{0xff, 0x55, 0x6, 0x0, 0x2, 0xa, d.port})
+	if err := binary.Write(bufOut, binary.LittleEndian, speed); err != nil {
+		return err
+	}
+	bufOut.Write([]byte{0xa})
+	d.writeBytesChannel <- bufOut.Bytes()
+
+	return nil
+}
+
+func (d *MotorDriver) adaptor() megapiMotorSerialAdaptor {
+	if a, ok := d.Connection().(megapiMotorSerialAdaptor); ok {
+		return a
+	}
+
+	log.Printf("%s has no MegaPi serial connector\n", d.Name())
+	return nil
+}

examples/megapi_motor.go → examples/serialport_megapi_motor.go

@@ -11,14 +11,15 @@ import (
 	"time"
 
 	"gobot.io/x/gobot/v2"
-	"gobot.io/x/gobot/v2/platforms/megapi"
+	"gobot.io/x/gobot/v2/drivers/serial/megapi"
+	"gobot.io/x/gobot/v2/platforms/serialport"
 )
 
 func main() {
 	// use "/dev/ttyUSB0" if connecting with USB cable
 	// use "/dev/ttyAMA0" on devices older than Raspberry Pi 3 Model B
-	megaPiAdaptor := megapi.NewAdaptor("/dev/ttyS0")
-	motor := megapi.NewMotorDriver(megaPiAdaptor, 1)
+	adaptor := serialport.NewAdaptor("/dev/ttyS0", serialport.WithName("MegaPi"))
+	motor := megapi.NewMotorDriver(adaptor, 1)
 
 	work := func() {
 		speed := int16(0)
@@ -36,7 +37,7 @@ func main() {
 	}
 
 	robot := gobot.NewRobot("megaPiBot",
-		[]gobot.Connection{megaPiAdaptor},
+		[]gobot.Connection{adaptor},
 		[]gobot.Device{motor},
 		work,
 	)

platforms/megapi/README.md

@@ -15,16 +15,19 @@ Please refer to the main [README.md](https://github.com/hybridgroup/gobot/blob/r
 package main
 
 import (
-  "gobot.io/x/gobot/v2"
-  "gobot.io/x/gobot/v2/platforms/megapi"
+  "fmt"
   "time"
+
+  "gobot.io/x/gobot/v2"
+  "gobot.io/x/gobot/v2/drivers/serial/megapi"
+  "gobot.io/x/gobot/v2/platforms/serialport"
 )
 
 func main() {
   // use "/dev/ttyUSB0" if connecting with USB cable
   // use "/dev/ttyAMA0" on devices older than Raspberry Pi 3 Model B
-  megaPiAdaptor := megapi.NewAdaptor("/dev/ttyS0")
-  motor := megapi.NewMotorDriver(megaPiAdaptor, 1)
+  adaptor := serialport.NewAdaptor("/dev/ttyS0", serialport.WithName("MegaPi"))
+  motor := megapi.NewMotorDriver(adaptor, 1)
 
   work := func() {
     speed := int16(0)
@@ -40,13 +43,13 @@ func main() {
   }
 
   robot := gobot.NewRobot("megaPiBot",
-    []gobot.Connection{megaPiAdaptor},
+    []gobot.Connection{adaptor},
     []gobot.Device{motor},
     work,
   )
 
   if err := robot.Start(); err != nil {
-		panic(err)
-	}
+    panic(err)
+  }
 }
 ```