Writing a custom event and sending it as a string to an API

Stefan Cazacu

I'm working on a personal project using a WinCE7 system and coding using C#. I need access to the system's GPIO and I have been provided with a GPIO api but little to no explanation or support from the developer. I've successfully used the api to set the output and get the input via polling but I need to set an interrupt driven mechanism. The api has a function that allows me to achieve this but i have been unable to figure out how to use it. The function looks like this: "BOOL GpioSetupInterruptPin(HANDLE hGPIO, PIN_GPIO_PORT port, UINT pin, INT_TRIGGER_MODE mode, INT_TRIGGER_POLARITY polarity, LPCWSTR szEventName, BOOL enable);"

I've been given the structures for the PORT, TRIGGER_MODE and TRIGGER_POLARITY and the following description for szEventName: "event name of a named event", but that is about it.

I'm new at event handling in c# and i've done a lot of tutorials and code samples i found on google but i'm not sure how to pass my event to the above function. I've followed a number of examples online but I still don't understand what i'm doing wrong.

Things i know i'm doing wrong in the code bellow: my event has no arguments, the code in red is not recognized by the compiler. I would really appreciate some help with this.

public partial class Form1 : Form

{

private void Interrupt_Setup()
{

hGPIO = GPIOapi.GpioOpenHandle(); //returns a handle to the gpio
GIPO_ON = true;
Debug.WriteLine("Driver open \n" + hGPIO);
string Trigger = "InputProcessUpdateHandler";
IntPtr handle = CreateEvent(IntPtr.Zero, false, true, Trigger); //used P/Invoke
GPIO_Output(); //set output pins
GPIO_Interrupt(Trigger);//configure interrupt

}

private void GPIO_Interrupt(string trigger)
{

bool ok;
//INTERRUPT DECALRATION
ok = GPIOapi.GpioSetupInterruptPin(hGPIO, port6, 4, GPIOapi.INT_TRIGGER_MODE.TRIGGER_MODE_EDGE,
GPIOapi.INT_TRIGGER_POLARITY.TRIGGER_POL_HIGH_RISING, trigger, true); //throws exception
if (!ok)
Debug.WriteLine("NO interrupt");
else
Debug.WriteLine("Interrupt set for:" + port6 + "04" + " at " + hGPIO);

}

private InputProcessor _inputProcessor = null;
public ShowToggle(InputProcessor inputProcessor)
{

_inputProcessor = inputProcessor;
_inputProcessor.updateHandeledBy += InputProcessUpdateHandler;

}
private void InputProcessUpdateHandler()
{

Debug.Write("execute");

}

}

public class InputProcessor
{

public event InputProcessUpdateHandler updateHandledBy = null;
public void Process(Label label)
{

if (updateHandledBy != null)
updateHandledBy(label);

}

}

Some of the sites i've looked at:

http://www.pinfaq.com/123/events-and-delegates-and-its-difference-dotnet-application

http://www.codeproject.com/Articles/11541/The-Simplest-C-Events-Example-Imaginable

http://timok.tumblr.com/post/57441520214/simplistic-event-example-in-c

http://www.codearsenal.net/2012/09/csharp-custom-event-handling.html

http://msdn.microsoft.com/en-us/library/windows/desktop/ms682396%28v=vs.85%29.aspx

http://stackoverflow.com/questions/12576944/triggering-event-in-c-sharp-from-c-dll?lq=1

http://stackoverflow.com/questions/17073386/raise-events-in-c-cli-dll-and-consume-in-c-sharp?lq=1

5 Replies

Know the answer? Post it — somebody with the same question will find it here.

Vulpes11y ago
Accepted answer
See if it will work if you remove [MarshalAs(UnmanagedType.LPArray)] leaving:

[DllImport("gpiosdk53.dll", SetLastError = true, CharSet = CharSet.Unicode)]
public static extern bool GpioSetupInterruptPin(IntPtr hGPIO, PIN_GPIO_PORT port, uint pin, INT_TRIGGER_MODE mode, INT_TRIGGER_POLARITY polarity, String szEventName, bool enable);

If it still doesn't work, can you tell me what exception you're getting?
Vulpes11y ago
Glad I could help :)

I know how frustrating it can be trying to call C functions when you don't have proper documentation or examples.
Stefan Cazacu11y ago
That fixed it! Thank you so much. I've been struggling with this for over 2 weeks. I've tried different p/invokes before, but it hasn't occurred to me to try again after i've changed the code (this was my 9th attempt). Thank you again
Stefan Cazacu11y ago
Hi, thanks for the help! I checked twice to see if i misspelt updateHandledBy but i missed it every time :P This is how I P/Invoke the function:

[DllImport("gpiosdk53.dll", SetLastError = true, CharSet = CharSet.Unicode)]
public static extern bool GpioSetupInterruptPin(IntPtr hGPIO, PIN_GPIO_PORT port, uint pin, INT_TRIGGER_MODE mode, INT_TRIGGER_POLARITY polarity, [MarshalAs(UnmanagedType.LPArray)] String szEventName, bool enable);

I've fixed the red lines but calling GpioSetupInterruptPin still throws an exception
Vulpes11y ago
I'll begin by saying that I know nothing at all about this API.

However, I do know something about calling C functions from C# and 'events' in C are not the same as events in C#. The links you've posted are therefore of no help :(

In fact, I see that you appear to have realized this already by calling CreateEvent and then attempting to pass the resulting named event to your GpioSetupInterruptPin function.

You haven't posted the P/Invoke signature you're using for the function but one reason why it might fail is if you don't have:

CharSet = CharSet.Unicode

in your DllImport attribute.

Thus is needed because LPCWSTR is a pointer to a unicode string whereas the default character set is ANSI.

Incidentally, the reasons for the red lines appear to be that you haven't defined the InputProcessUpdateHandler delegate anywhere and there's a typo in the updateHandeledBy event which should be updateHandledBy. However, as mentioned earlier, I don't think you need this stuff anyway.