[fpc-pascal] Question on programming serial communication.

Marc Santhoff M.Santhoff at t-online.de
Tue Feb 26 01:45:15 CET 2008

Am Montag, den 25.02.2008, 18:13 +0100 schrieb Rainer Hantsch:
> | >    I only want to use sme kind of API, Class, Object or set of procedures
> | >    which allows me similar things as were possible with the FOSSIL 
> | >    driver:
> | >    - Buffered I/O
> | >    - Flow Control as I need (RTS/CTS, XON/XOFF, Both, None)
> | >    - Direct Control of control lines like DTR, ...
> | >    - Possibilities for monitoring fill level of buffers, to force
> | >      them to be erased (made empty), ...
> | 
> | In Linux you simply open() the /dev/ttySxx device and then read() and
> | write() to it. This is for data, for other stuff (e.g. flow
> | control, ...) can be done via ioctl() (please excuse the C syntax). But
> | as Horacio already said you probably go better with a wrapper, e.g.
> | Synaser or TSerial (but I didn't use either).


> As far as I could find out some years ago, the /dev/ttySxx are having no 
> buffer.

I think that is a matter of your OS and maybe a question of port
settings, but I'm not really sure. ;)

> --> "BLOCKING" is the magic word which is the problem.   :-(

That problem is easily solved. I'm only using serial.pp for reading a
dumb and slow dmm, but in principle (on FreeBSD):

fCom := fpOpen('/dev/cuaa0', O_RDWR OR O_NOCTTY );//OR O_NONBLOCK);

See the commented tail of that line? Linux must have something similar
(IMHO). That way you can switch to the expected behaviour.

After opening some settings need to be done:

	tios: termios;
	fillchar(tios, sizeof(tios), #0);

	tios.c_ispeed := B1200;
	tios.c_ospeed := B1200;
	tios.c_cflag := CREAD or CLOCAL or CS7 or CSTOPB;
	tios.c_oflag := 0;
	tios.c_iflag := IGNBRK OR IGNPAR;
	tios.c_lflag := 0;
	r := tcsetattr(fCom, TCSANOW, tios);

All of that could be done using:

	SerSetParams(fCom, 1200, 7, NoneParity, 2, []);

but for me that did not set all I needed, though I don't remember what
was missing.

And for controlling the lines you can do sth. lke:

	SerSetRTS(fCom, FALSE);

and the same for other lines. Look into the serial unit and also the
tios unit. On FreeBSD termios(4) has a lot of information (and it states
every line has an input queue aka buffer).


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