How to know data incoming from serial port?

QNX DEVELOPERS Realtime and Embedded
1

Dear Sir,

I developed my App by serial driver and I can read and write data by serial port ("/dev/ser1"). The physical connection is shown as below:

PC------/dev/ser1-------Modem---------Externel Device(Data Device)

Now my question is: The Data Device will send data to PC randomly, I think the Mode of getting Data by polling the serial port periodically makes on sense and it will take most CPU process time. Now my question is, how do I know data incoming from serial port without polling the serial port? by Interrupt or some Signal else? or something like the code in Microsoft visual basic serial communication event: comRing, ComReceive, ComSend, etc?

Can someone kindly give some example code?

Thanks.

Alex Yu

2

I use ionotify() with a SIGEV_PULSE_INIT sigevent for notifications that serial data is available:

SIGEV_PULSE_INIT( &dataEvent, connectionId, SIGEV_PULSE_PRIO_INHERIT, 5, 0);

// Re-register for notifications of received data
status = ionotify( comPortFd, _NOTIFY_ACTION_POLLARM, _NOTIFY_COND_INPUT, dataEvent);
if( status == -1)
{
	Log( LOG_ERRORS, "\tDriverDataRegister() ionotify failed: %s\n", strerror( errno));
}
// If data is currently available
else if( status & _NOTIFY_COND_INPUT)
{
	int bytesWaiting;
	if( (bytesWaiting=tcischars( comPortFd)) > 0)
	{
		Log( LOG_DEV_DATA, "DriverDataRegister() %d bytes available, forwarding notification pulse\n", bytesWaiting);
		// Send a pulse to our channel
		MsgSendPulse( dataEvent->sigev_coid, dataEvent->sigev_priority, 
			  dataEvent->sigev_code, dataEvent->sigev_value.sival_int+1);
	}
	else
	{
		Log( LOG_ERRORS, "\tSerial driver says data is ready, but tcischars() <= 0\n");
	}
	status = 0;
}
3

Am I missing something here? What’s wrong with just calling read()? It will block on the serial port until their is data available (one char at a time if that is the size of the read). Just make sure the serial port is in raw mode before you call read (otherwise it will block until you have a “line” of data).

Rick…

4

Rick, what if you don’t want to program to block, handling other events as well. Personnaly I prefer having a thread handle the read. The thread can deal with the protocol, error handling and such. When the data is received the thread notifies another thread.

5

select() works in that situation as well. Any solution which doesn’t involve polling is a better solution than one which polls. For that matter I also avoid threads, unless it is the simplest solution - just because of the complexity and risk using threads adds.

Rick…