xlCanTransmit() function does not work properly - c++

Question

I am trying to send CAN Frames with xlCanTransmit method. The problem is that it returns 0 (XL_SUCCESS), but the frame is empty. there are only zeroes in the Frame.
IVxlApi.s_xl_event eventMsg = new IVxlApi.s_xl_event();
...
...
xlStatus = dll.xlCanTransmit(GlobalConfig.g_xlPortHandle, GlobalConfig.g_xlChannelMask[channelIndex],
pEventCount, eventMsg.getPointer());
After Calling the function xlCanTransmit() the frame is sent, but there is no data in it. The function is called from dll file and you can't debug it.
My mapped Structure
public static class s_xl_event extends Structure {
public byte tag;
public byte chanIndex;
public byte[] transId = new byte[SHORT];
public byte[] portHandle = new byte[SHORT];
public byte flags;
public byte reserved;
public byte[] timeStamp = new byte[LONG];
public s_xl_tag_data tagData;
#Override
public void read() {
// read from native memory, populate tag
super.read();
// set union type based on tag
switch (tag) {
case XL_RECEIVE_MSG:
case XL_TRANSMIT_MSG:
tagData.setType(s_xl_can_msg.class);
break;
case XL_CHIP_STATE:
tagData.setType(s_xl_chip_state.class);
break;
case XL_LIN_MSG:
tagData.setType(s_xl_lin_msg_api.class);
break;
case XL_SYNC_PULSE:
tagData.setType(s_xl_sync_pulse.class);
break;
case XL_RECEIVE_DAIO_DATA:
tagData.setType(s_xl_daio_data.class);
break;
case XL_TRANSCEIVER:
tagData.setType(s_xl_transceiver.class);
break;
case XL_RECEIVE_DAIO_PIGGY:
tagData.setType(s_xl_daio_piggy_data.class);
break;
case XL_KLINE_MSG:
tagData.setType(s_xl_kline_data.class);
break;
default:
// add default type or throw exception etc.
tagData.setType(s_xl_can_msg.class);
break;
}
// now read tagData from native memory
tagData.read();
}
#Override
protected List<String> getFieldOrder() {
return Arrays.asList("tag", "chanIndex", "transId", "portHandle", "flags", "reserved", "timeStamp", "tagData");
}
}
CAN Frame in CANoe Trace
enter image description here
The function on the native side looks like this
DECL_STDXL_FUNC(xlCanTransmit, XLCANTRANSMIT, (
XLportHandle portHandle,
XLaccess accessMask,
unsigned int* pEventCount,
void* pEvents)
);
My mapping in java
short xlCanTransmit(long portHandle, long accessMask, IntByReference pEventCount, Pointer pEvents);
I wrote some random data manually and called the xlCanTransmit() function.
But in CANoe trace I see only empty frame with no data and id.
My send function in java
public short send(String txID, String dlc, String[] data, int channelIndex) {
short xlStatus = IVxlApi.XL_ERROR;
IntByReference pEventCount = new IntByReference(1);
IVxlApi.s_xl_event eventMsg = new IVxlApi.s_xl_event();
eventMsg.tag = IVxlApi.XL_TRANSMIT_MSG;
eventMsg.tagData.msg.id[0] = 2;// = Long.parseLong(txID);
eventMsg.tagData.msg.dlc[0] = 8;// = Short.parseShort(dlc);
eventMsg.tagData.msg.flags[0] = 0;
eventMsg.tagData.msg.data[0] = Byte.parseByte(data[0]);
eventMsg.tagData.msg.data[1] = Byte.parseByte(data[1]);
eventMsg.tagData.msg.data[2] = Byte.parseByte(data[2]);
eventMsg.tagData.msg.data[3] = Byte.parseByte(data[3]);
eventMsg.tagData.msg.data[4] = Byte.parseByte(data[4]);
eventMsg.tagData.msg.data[5] = Byte.parseByte(data[5]);
eventMsg.tagData.msg.data[6] = Byte.parseByte(data[6]);
eventMsg.tagData.msg.data[7] = Byte.parseByte(data[7]);
/*if(true){
eventMsg.tagData.msg.id |= IVxlApi.XL_CAN_EXT_MSG_ID;
}*/
eventMsg.write();
xlStatus = dll.xlCanTransmit(GlobalConfig.g_xlPortHandle, GlobalConfig.g_xlChannelMask[channelIndex],
pEventCount, eventMsg.getPointer());
eventMsg.read();
return xlStatus;
}
CAN Frame in CANoe Trace
enter image description here
After calling tagData.read() (line 475) the data initialized with zeroes
enter image description here

Answer 1

The return value of 0 indicates the function preformed properly on the native side, but you haven't copied the native memory back to Java.
This is normally done automatically when you pass a Structure in a function, but you have passed the Pointer to the structure instead. Your last argument is eventMsg.getPointer(). JNA doesn't know how the Pointer maps to your structure until you tell it to do so, and in the current way you're calling it requires using read() to copy the value back to JNA.
You could probably get the results you want by just executing eventMsg.read() after calling the function, but the better solition is to pass the Structure to the function in the first place and let JNA do the conversion to Pointer and auto-read() for you. Change your function call to pass eventMsg as the argument.