scala-ads-client

Beckhoff TwinCAT ADS client for the Scala language

About

This is a Scala-idiomatic reactive client for Beckhoff TwinCAT PLC.

Features

• Get a continuous stream of notifications for PLC variables as Monix Observables.
• Compose and transform Observables to achieve more complex behavior.
• Streaming of elements in an Observable to PLC variables
• Easy reading and writing of custom data types (case classes) to PLC structs
• Efficient and typesafe reading and writing of many variables at once using ADS SUM commands
• Fully non-blocking async IO.

Built on top of monix and monix-nio.

Documentation

Connect

The AdsClient object provides a connect method which will asynchronously connect to an ADS router.

Important a route must be added to the ADS router to allow traffic from the source AMS ID.

import com.vroste.adsclient._
import com.vroste.adsclient.codec.AdsCodecs._

import monix.eval.Task
import monix.execution.Scheduler.Implicits.global

val settings = AdsConnectionSettings(AmsNetId.fromString("10.211.55.3.1.1"), 801, AmsNetId.fromString("10.211.55.3.10.10"), 123, "localhost")
val clientT: Task[AdsClient] = AdsClient.connect(settings)

// Example, in a real application you should flatMap the task
clientT.runOnComplete {
 case Success(adsClient) => // Do stuff with the client
 ...
}

Reading

To read a PLC variable once:

val client: AdsClient = AdsClient.connect(...)
val result: Task[Int] = client.read("MAIN.myIntegerVar", int)

This will create a variable handle, read using the handle and release the handle.

Reading many variables at once

To read many variables efficiently and atomically, first create a list of the variable names and their respective codecs and then call the read() method.

val variables = VariableList("MAIN.var1", int) + ("MAIN.var2", bool)
val result: Task[Int :: Bool :: HNil] = client.read(variables)

The result will be a shapeless HList, which you can convert to a tuple using result.tupled or to a case class using Generic[MyCaseClass].from(hlistResult).

Codecs

The int parameter to read() in the example above is the codec which translates between the PLC datatype and the scala datatype. Because Scala does not have a 1-to-1 corresponding type for all PLC datatypes, the codec has to be provided explicitly. Codecs for unsigned integer types will map PLC values to the >=0 range of the appropriate Scala data type.

Available codecs are named after the PLC datatype, in the AdsCodecs object:

Codec	PLC data type	Scala data type	Notes
bool	BOOL	Boolean
byte	BYTE	Byte
word	WORD	Int	16 bit unsigned integer
dword	DWORD	Long	32 bit unsigned integer
sint	SINT	Int	8 bit signed integer
usint	USINT	Int	8 bit unsigned integer
int	INT	Short	16 bit signed integer
uint	INT	Int	16 bit unsigned integer
dint	INT	Int	32 bit signed integer
udint	INT	Long	32 bit unsigned integer
real	REAL	Float	32 bit floating point number
lreal	LREAL	Double	64 bit floating point number
string	STRING(80)	String	80 is the default string length
stringN(maxLength)	STRING(maxLength)	String	String of the given maximum length (maxLength + 1 bytes)
array[T](length, codecForT)	ARRAY [1..length] OF T	List[T]
date	DATE	LocalDate
dateAndTime	DATE_AND_TIME	LocalDateTime
timeOfDay	TIME_OF_DAY	LocalTime
time	TIME	FiniteDuration

Notifications

The AdsClient can provide notifications for changes to a PLC variable as an Observable. This is the recommended way to repeatedly check a variable for changes without polling.

val notifications: Observable[AdsNotification[String]] = client.notificationsFor("MAIN.myStringVar", string)

// Perform further operations on this observable, such as filtering, mapping, joining with observables
// for other PLC variables, etc. 

notifications.subscribe(Consumer.foreach(value => println(s"Got value ${value.value} at timestamp ${value.timestamp}"))

Note that the notifications are registered for each subscribe() and that they are only started upon subscription. The notification is ended when the subscription stops.

Writing

The ADS client provides a method for writing to a PLC variable once. This methods returns a Task which is completed when the write is complete.

val writeComplete: Task[Unit] = client.write("MAIN.myUnsignedIntegerVar", uint)

Writing an Observable

When you have an Observable of values and you want to write (stream) it to a PLC variable for each emitted value, use the following:

val strings = Observable.interval(15.seconds)
    .take(10)
    .map(value => s"The next value is ${value}")
    
val consumer = client.consumerFor("MAIN.myStringVar", string)

val done: Task[Unit] = strings.consumeWith(consumer)

Writing many variables at once

To write many variables at once efficiently, create a list of the variables and their respective codecs first. Then construct the value as an HList (or convert from a case class or tuple).

val variableList = VariableList("MAIN.var1", int) + ("MAIN.var2", string) + ("MAIN.var4", int) + ("MAIN.var5", bool)

val values = 3 :: "Dummy" :: 42 :: true
client.write(variableList, values)

Custom datatypes

Codecs can be composed together to map to custom data types such as your own value classes or case classes

Value classes

A value class can be mapped to a PLC primitive value type. This allows you to write Scala code with more descriptive and possibly restricted types. The automatic conversion is thanks to Shapeless.

case class Degrees(value: Int) extends AnyVal

val degreesCodec: Codec[Degrees] = uint.as

STRUCTs to case classes

Using the same technique, PLC STRUCTs can be mapped to a Scala case class as follows.

As an example, assume that in the PLC code a STRUCT with 3 members is defined:

TYPE MyCustomType:
STRUCT
  a: INT := 1;
  b: INT := 1;
  c: BOOL := FALSE;
END_STRUCT
END_TYPE

Define the data type and codec on the Scala side as follows:

case class MyDummyObject(a: Int, b: Int, c: Boolean)

val myDummyObjectCodec: Codec[MyDummyObject] = (int :: int :: bool).as