Invalid Checksum

[PieterVO]

Hi,

I get an invalid checksum error when I send a state of a custom element from the central to a peripheral. This is only the case when the CustomElementType = .String. Can you check if it's a general problem? So to be clear: I try to send some information (a string) from the central to a peripheral, so I'm trying to implement bidirectional communication.

Thanks

[robreuss]

Hi,

I just tested and was unable to reproduce. Test procedure below.

I generally only see the invalid checksum errors when sending large amounts of motion data on a less powerful device like an iPhone 4s - we're talking 100s of messages/sec - so it would be strange to see it when sending a small string. Are you sending small strings, large strings, or a fast stream of small strings?

Feel free to send more info about what you are attempting to do, as well as code if you like, and I'm happy to help getting it to work.

Rob

I tested this way:

• I used the existing "Keyboard" custom element
• I used the existing "receivedDebugViewDoubleTap" event on the iOS Central sample app to trigger sending from Central to Peripheral
• I used the following code to send the string value:

        let keyboard = controller.elements.custom[CustomElementType.Keyboard.rawValue]!
        keyboard.value = "A string"
        controller.sendElementStateToPeripheral(keyboard)

• I set a handler in the viewDidLoad method on the iOS Peripheral sample app to catch the incoming string:

        if let element: Element = VgcManager.elements.elementFromIdentifier(CustomElementType.Keyboard.rawValue) {

            element.valueChangedHandlerForPeripheral = { (element: Element) in

                print("Custom element handler fired for \(element.name) with value \(element.value)")

                self.peripheralControlPadView.flashView.backgroundColor = UIColor.brownColor()
                UIView.animateWithDuration(0.05, delay: 0.0, options: .CurveEaseIn, animations: {
                    self.peripheralControlPadView.flashView!.alpha = 1
                    }, completion: { finished in
                        self.peripheralControlPadView.flashView!.alpha = 0
                })

            }
        }

[PieterVO]

Hi,

Thank you for your help and excuse me if I'm writing some bad English.

I'm creating a card game. The Apple TV shuffles the deck of cards and then divide them among the players. I use a string to do this (each card has a number), with a delimiter (space).

Here the code I used to send the string value:

public func devide(){
    if (!hands.isEmpty){
        hands.removeAll()
    }
    self.deck = self.shuffleInPlace(deck)
    var temp = [Int]()
    for var i = 1;i < (deck.count+1);++i{
        temp.append(deck[i-1])
        if ((i%8 == 0)){
            hands.append(temp)
            temp.removeAll()
        }

    }

    //TODO check if right amount of controllers
    for controller in VgcController.controllers(){
        let playerI: Int = controller.playerIndex.rawValue
        if playerI > 0 {
            var str = ""
            str.appendContentsOf("\(hands[playerI-1][0])")
            for var i = 1; i < hands[playerI-1].count; ++i{
                str.appendContentsOf(" \(hands[playerI-1][i])")
            }
            let element: Element = controller.elements.custom[CustomElementType.Hand.rawValue]!
            element.value = str
            controller.sendElementStateToPeripheral(element)
        }
    }

    print("cards handed out")
}

The string is correctly generated, so don't worry about that.

The code I used for the handler (runs on an iPhone 5):

func createHandHandler(){
    //to check if cards are changed
    if let element: Element = VgcManager.elements.elementFromIdentifier(CustomElementType.Hand.rawValue) {

        element.valueChangedHandlerForPeripheral = { (element: Element) in

            print("Hand element handler fired for \(element.name) with value \(element.value)")
            self.game.updateHand(element)
        }

        print("created handler for Hand")

    }
}

Again, thank you for your help!

[PieterVO]

I've solved it for now. When I let the string begin with "hand", it doesn't give an invalid checksum error. So the final string I send looks like this then: "hand 1 2 3 4 5 6 7 8" I still doesn't get it to work with "1 2 3 4 5 6 7 8".

[robreuss]

Glad you got it working for you. Thanks to your examples of working and non-working strings, I was able to figure out the problem. It had to do with how the checksum was calculated for different data types. I was making an assumption that a String value would not be able to be cast into a Float, but since you sent along numbers, it exposed my flawed logic. I'm now handling Strings more explicitly. I'll be pushing the change out in the next day or so.

Note that you also have a Data (NSData) data type available for use. The idea behind that is that you would use NSKeyedArchive to archive your hand object and send that along to the Peripheral. It's a bit more complex, but will give you the ability to easily extend the information set that you are sending to the Peripheral

[robreuss]

I should note that I'm running 7.2 beta 3 - not sure if that makes a difference.

[PieterVO]

I'm using 7.2 beta 3 too.I will look to the Data option.Thank you for your help!