tmm33@leah.Albany.Edu (Terry McCoy) (09/27/89)
Does anyone known what would be needed to create a function similar to getc()
that would return control to the calling function if the buffer was empty.
My application running SCO XENIX 2.3 has opened a serial port and monitors it
for incoming data. The data is coming as packets. I have tried using the
system functions getc, fread and read but they all wait for data to arrive
before returning control back to the calling function.
I have looked at the getc function in the stdio.h header file and noticed that
it calls a function _filbuf. I think that this function is located within the
kernal and controls the pointers, flags and the counter within the structure
FILE. Any information on how this function works or how I could tell if data
has arrived at the serial port without waiting would be helpful.
Terry McCoy
SUNY Albany National Lightning Detection Network
Research Foundation - State University of New York at Albany
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Albany, NY 12222davidsen@crdos1.crd.ge.COM (Wm E Davidsen Jr) (09/28/89)
The usual way to do this is to use the ioctl which sets the read non-blocking. This will return a byte count of zero if there is no data. This is portable and more likely to continue working than playing around with things inside macros. -- bill davidsen (davidsen@crdos1.crd.GE.COM -or- uunet!crdgw1!crdos1!davidsen) "The world is filled with fools. They blindly follow their so-called 'reason' in the face of the church and common sense. Any fool can see that the world is flat!" - anon
cpcahil@virtech.UUCP (Conor P. Cahill) (09/28/89)
In article <2056@leah.Albany.Edu>, tmm33@leah.Albany.Edu (Terry McCoy) writes: > I have looked at the getc function in the stdio.h header file and noticed that > it calls a function _filbuf. I think that this function is located within the > kernal and controls the pointers, flags and the counter within the structure Nope. _filbuf is a stdio library function that eventually uses read(2) to fill the buffer. > FILE. Any information on how this function works or how I could tell if data > has arrived at the serial port without waiting would be helpful. Since you are reading data off of the serial port you should use the following type of code: #include <fcntl.h> fd = open(TTY_PORT,O_RDWR+O_NDELAY....) if( (cnt=read(fd,buffer,512)) > 0 ) /* process the data */ else if( cnt == -1 ) /* handle read failure */ /* else cnt = 0 (no data available) */ -- +-----------------------------------------------------------------------+ | Conor P. Cahill uunet!virtech!cpcahil 703-430-9247 ! | Virtual Technologies Inc., P. O. Box 876, Sterling, VA 22170 | +-----------------------------------------------------------------------+
les@chinet.chi.il.us (Leslie Mikesell) (09/28/89)
In article <2056@leah.Albany.Edu> tmm33@leah.albany.edu.UUCP (Terry McCoy) writes: >Does anyone known what would be needed to create a function similar to getc() >that would return control to the calling function if the buffer was empty. You can set up a signal handler for SIGALRM and use alarm() to interrupt the read(). Or, use fcntl() to set O_NDELAY so read() will return if no characters are available. (Don't forget to turn it off before any write()'s). Or, use ioctl() and set the c_cc[VMIN] and c_cc[VTIME] fields in the termio struct to zeros and turn off ICANON. (See termio(7)). Depending on the application, it may also be possible to do the input in a separate process which can then block without problems. Les Mikesell
SATAM@ecs.umass.edu (10/01/89)
Read without wait. you can try read with NO_DELAY flag. the exact constant is given in <fcntl.h>. The read call will return -1 if there is no character in the buffer. Also take care to open the port in raw mode. Otherwise, the mysterious four character buffering will be a headache. - K G Satam email "satam@ecs.umass.edu"