QUESTION:
We are working on an application that is doing canonical reads and
writes on a tty port. As I understand, a canonical read only receives
the data when in our case a is sent to indicate the end of the
data block. We are getting all the data fine minus the , which is
ok. However, when we do a write to the port, all the data is being
sent, and again, the is the end of block flag, and it is left
out of the transmission. However, the device on the other end, a
special hand held terminal, is programmed to expect a to
signify the end of data. Is there anyway to get the system to send
the using canonical reads?
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A: From Info (Understanding the POSIX Line Discipline):
In canonical mode input processing, terminal input is processed
in units of lines. A line is deliminted by a new-line (ascii LF)
character, and end-of-file (EOF) character, or an end-of-line(EOL)
character. This means that a program attempting to read will be
blocked until an entire line has been typed or a signal has been
received. Also, regardless of how many characters are requested in
the read, no more than one line will be returned.
ICANON applies only to input mode (read), not to output mode (write).
The usual posix settings are (- means OFF, + means ON):
-INLCR Map NL to CR on input
-IGNCR Ignore CR
+ICRNL Map CR to NL on input
------
+OPOST Postprocess output (this must be ON for other for
the other flags below to work)
+ONLCR Map NL to CR-NL on output
-OCRNL Map CR to NL on output
-ONLRET Map NL to CR on output
You probably want to experiment with some of these settings until
you are receiving/sending what you want.
Another choice is to turn off OPOSTand explicitly write out
a '\r'instead of (or in addition to) a '\n'.
For instance, "write(fn,"hello\r",6);
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This item was created from library item Q524439 1992 IJHF1
S e a r c h - k e y w o r d s:
CANONICAL COMMUNICATIO HAVING IJHF1 IX MAR91 PROBLEM READS RISCC
RISCSYSTEM SOFTWARE TTY
WWQA: ITEM: RTA000017834 ITEM: RTA000017834
Dated: 07/1998 Category: RISCAPRT
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