Serial Port Callback Stops Responding

[DieselPower]

I have a PXI system running Pharlap.  I have an 16 port serial card PXI-8430.  This is one of 12 systems with very similar configuration.

One of those systems randomly loses connection to one particular serial device, but I am communicating with three of these devices on three different ports.  I am also communicating to two other different devices on different ports and those devices do not lose connection.  The ports that disconnect are no adjacent.  Why would those ports stop responding to the callback? 

I have installed a serial port sniffer and I can see the request and response in both directions so I know the traffic is there.  The callback has simply stopped calling back.

The only way to fix it is to cycle PXI power.  Disconnecting from it and killing the callback is not sufficient.

Is it necessary to destroy a ComCallback when one is Installed? 

int Timer_Port_Open(int CurrentTimer)
{
	// Open and configure the port
	HWTimers[CurrentTimer].gBaud		= 38400;
	HWTimers[CurrentTimer].gParity	= 0;	// no parity checking
	HWTimers[CurrentTimer].gDataBits	= 8;	// 8-bit characters
	HWTimers[CurrentTimer].gStopBits	= 1;	// 1 stop bit
	HWTimers[CurrentTimer].gInQSize	= 512;	// 512-byte input queue
	HWTimers[CurrentTimer].gOutQSize	= -1;	// disable the output queue (synchronous writes)	
	
	// Initialize members
	HWTimers[CurrentTimer].TimerValue	= 0;	//

	if (OpenComConfig (HWTimers[CurrentTimer].gPortNum, NULL, HWTimers[CurrentTimer].gBaud, HWTimers[CurrentTimer].gParity, HWTimers[CurrentTimer].gDataBits, HWTimers[CurrentTimer].gStopBits, HWTimers[CurrentTimer].gInQSize, HWTimers[CurrentTimer].gOutQSize) < 0)
		return -1;
	
	InstallComCallback (HWTimers[CurrentTimer].gPortNum, LWRS_RXFLAG, -1, TERM_CHAR, Timer_Message_Received, NULL);
	
	Timer_Port_SendMessage(CurrentTimer);
	
	return 0;
}

extern void CVICALLBACK Timer_Message_Received (int COMPort, int eventMask, void *callbackData)
{
	static char receivedMsg[64];
	float	TimerValue = 0;
	int TempPort = -1;
	
	do
	{
		TempPort++;
	} while (HWTimers[TempPort].gPortNum != COMPort);
	
	if (ComRdTerm (HWTimers[TempPort].gPortNum, receivedMsg, sizeof(receivedMsg) - 1, TERM_CHAR) > 0)
	{
		if (strlen(receivedMsg) < 20)
			strncpy(HWTimers[TempPort].msg, receivedMsg+10,39);

		//DebugPrintf("%s\n\n", receivedMsg);  
	}
		
	HWTimers[TempPort].TimerValue = atof(HWTimers[TempPort].msg);
	
	return;
}

[gdargaud]

I'm just going around the messages with no answers in the forum, and several things strike me in your code:

- neither ComReadTerm() nor strncpy() add a terminating ASCII NUL at the end of the buffer, so I'm pretty sure this code will crash randomly.

- you need to retrieve the value returned by ComReadTerm() for that.

- why do you skip the 1st 10 bytes of the reply (maybe it's useless wrapper) ?

- why do you have an infinite loop at the start of your callback ?

[DieselPower]

- neither ComReadTerm() nor strncpy() add a terminating ASCII NUL at the end of the buffer, so I'm pretty sure this code will crash randomly.

Generally I initialize strings.  In this case I did not, but I will add it.

- you need to retrieve the value returned by ComReadTerm() for that.

Are you saying I should retrieve the number of bytes received as a test case on that call rather than just making the call?

- why do you skip the 1st 10 bytes of the reply (maybe it's useless wrapper) ?

The message has a header and then a timer value.  I only need the timer value.

- why do you have an infinite loop at the start of your callback ?

It is not infinite.  It could be a for loop iterating through the number of timers I'm talking to, but this one works as well.  I agree it is likely bad programming and I'm not sure why I did it this way.

I ended up solving the problem by remaking the serial port whenever it would time out.  It is only one cell that this happens in, and only one type of serial device vs. the many different kinds I am using.

Thank you.

[gdargaud]

I should look more like:

if (HWTimers[TempPort].gPortNum != COMPort) return;
	
int Nb=ComRdTerm (HWTimers[TempPort].gPortNum, receivedMsg, sizeof(receivedMsg) - 1, TERM_CHAR)
if (Nb<=0) return; // And possibly error message
receivedMsg[Nb]='\0'; // Now it's a proper string !
if (Nb < 20 and Nb>10) {
 strncpy(HWTimers[TempPort].msg, receivedMsg+10,39);
 HWTimers[TempPort].msg[39-10]='\0'; // Must be terminated manually
}