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Programming serial interface question (linux)

P: n/a
hi, i have this piece of code:

---
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <termios.h>
#include <stdio.h>

/* baudrate settings are defined in <asm/termbits.h>, which is
included by <termios.h> */
#define BAUDRATE B38400
/* change this definition for the correct port */
#define MODEMDEVICE "/dev/ttyS1"
#define _POSIX_SOURCE 1 /* POSIX compliant source */

#define FALSE 0
#define TRUE 1

volatile int STOP=FALSE;

main()
{
int fd,c, res;
struct termios oldtio,newtio;
char buf[255];
/*
Open modem device for reading and writing and not as
controlling tty
because we don't want to get killed if linenoise sends
CTRL-C.
*/
fd = open(MODEMDEVICE, O_RDWR | O_NOCTTY );
if (fd <0) {perror(MODEMDEVICE); exit(-1); }

tcgetattr(fd,&oldtio); /* save current serial port settings
*/
bzero(&newtio, sizeof(newtio)); /* clear struct for new port
settings */

/*
BAUDRATE: Set bps rate. You could also use cfsetispeed and
cfsetospeed.
CRTSCTS : output hardware flow control (only used if the
cable has
all necessary lines. See sect. 7 of Serial-HOWTO)
CS8 : 8n1 (8bit,no parity,1 stopbit)
CLOCAL : local connection, no modem contol
CREAD : enable receiving characters
*/
newtio.c_cflag = BAUDRATE | CRTSCTS | CS8 | CLOCAL | CREAD;

/*
IGNPAR : ignore bytes with parity errors
ICRNL : map CR to NL (otherwise a CR input on the other
computer
will not terminate input)
otherwise make device raw (no other input processing)
*/
newtio.c_iflag = IGNPAR | ICRNL;

/*
Raw output.
*/
newtio.c_oflag = 0;

/*
ICANON : enable canonical input
disable all echo functionality, and don't send signals to
calling program
*/
newtio.c_lflag = ICANON;

/*
initialize all control characters
default values can be found in /usr/include/termios.h, and
are given
in the comments, but we don't need them here
*/
newtio.c_cc[VINTR] = 0; /* Ctrl-c */
newtio.c_cc[VQUIT] = 0; /* Ctrl-\ */
newtio.c_cc[VERASE] = 0; /* del */
newtio.c_cc[VKILL] = 0; /* @ */
newtio.c_cc[VEOF] = 4; /* Ctrl-d */
newtio.c_cc[VTIME] = 0; /* inter-character timer
unused */
newtio.c_cc[VMIN] = 1; /* blocking read until 1
character arrives */
newtio.c_cc[VSWTC] = 0; /* '\0' */
newtio.c_cc[VSTART] = 0; /* Ctrl-q */
newtio.c_cc[VSTOP] = 0; /* Ctrl-s */
newtio.c_cc[VSUSP] = 0; /* Ctrl-z */
newtio.c_cc[VEOL] = 0; /* '\0' */
newtio.c_cc[VREPRINT] = 0; /* Ctrl-r */
newtio.c_cc[VDISCARD] = 0; /* Ctrl-u */
newtio.c_cc[VWERASE] = 0; /* Ctrl-w */
newtio.c_cc[VLNEXT] = 0; /* Ctrl-v */
newtio.c_cc[VEOL2] = 0; /* '\0' */

/*
now clean the modem line and activate the settings for the
port
*/
tcflush(fd, TCIFLUSH);
tcsetattr(fd,TCSANOW,&newtio);

/*
terminal settings done, now handle input
In this example, inputting a 'z' at the beginning of a line
will
exit the program.
*/
while (STOP==FALSE) { /* loop until we have a terminating
condition */
/* read blocks program execution until a line terminating
character is
input, even if more than 255 chars are input. If the
number
of characters read is smaller than the number of chars
available,
subsequent reads will return the remaining chars. res will
be set
to the actual number of characters actually read */
res = read(fd,buf,255);
buf[res]=0; /* set end of string, so we can
printf */
printf(":%s:%d\n", buf, res);
if (buf[0]=='z') STOP=TRUE;
}
/* restore the old port settings */
tcsetattr(fd,TCSANOW,&oldtio);
}
---

it prints the data that comes from the ttyS0 port. now i have 2
questions:

1. can it be that this code does not get all data from the port and

2. anyone good at decoding such signals?

THANKS:)
Nov 13 '05 #1
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3 Replies


P: n/a
Math55 <ma******@t-online.de> wrote:
hi, i have this piece of code:
Which is full of non-standard function, include file etc. Thus you're
unfortunately rather off-topic in comp.lang.c, where only the standard
C language is the topic, but not system-specific extensions. I would
strongly recommend that you take this to e.g. comp.unix.programmer.

<mostly OT> #define MODEMDEVICE "/dev/ttyS1" volatile int STOP=FALSE;
No reason to make this a volatile and global variable.
main()
You better declare main() as returning int or you might get into
trouble with a C99 compliant compiler.
{
char buf[255];
<snipped>
while (STOP==FALSE) {
res = read(fd,buf,255);
buf[res]=0;
This will fail badly when a) read() returns a negative number,
indicating failure, or b) you get exactly 255 chars, in which
cases you would be writing outside the boundaries of your buffer.
printf(":%s:%d\n", buf, res);
if (buf[0]=='z') STOP=TRUE;
}
Why not simply write it as

do
{
res = read(fd, buf, 254)
...
} while ( buf[0] != 'z' );
/* restore the old port settings */
tcsetattr(fd,TCSANOW,&oldtio);
}
You're missing a return statement - even if you didn't explicitely
wrote that main() returns an int a C89 compiler will automatically
default to this type.
it prints the data that comes from the ttyS0 port. now i have 2
No, you're reading from /dev/ttyS1, see your #define of MODEMDEVICE.
questions: 1. can it be that this code does not get all data from the port and
Yes. But you don't even check yet for all possible errors.
2. anyone good at decoding such signals?


What signals?
</mostly OT>
Regards, Jens
--
_ _____ _____
| ||_ _||_ _| Je***********@physik.fu-berlin.de
_ | | | | | |
| |_| | | | | | http://www.physik.fu-berlin.de/~toerring
\___/ens|_|homs|_|oerring
Nov 13 '05 #2

P: n/a
ma******@t-online.de (Math55) wrote:
hi, i have this piece of code:

---
[code snipped]
---

it prints the data that comes from the ttyS0 port. now i have 2
questions:

1. can it be that this code does not get all data from the port and
The code is copied from the Linux Serial-Programming-HOWTO,
(Section 3.1, Canonical Input Processing) which does indeed
work, but is perhaps not the best example of programming ever
distributed.
2. anyone good at decoding such signals?
There are several people who would be quite happy to go through
that example line by line and make comments, additions,
corrections, but not in comp.lang.c.

Please repost your query to an appropriate Linux related
newsgroup (try comp.os.linux.development.apps, for example), and
I'm quite sure you'll get a great deal of help. (I have a
complete set of replacement programs for each section in the
HOWTO. I understand that at least one other person has also
rewritten the entire document. Hence the potential for detailed
help is high.)
THANKS:)


--
Floyd L. Davidson <http://web.newsguy.com/floyd_davidson>
Ukpeagvik (Barrow, Alaska) fl***@barrow.com
Nov 13 '05 #3

P: n/a
Floyd Davidson <fl***@barrow.com> wrote in message news:<87************@barrow.com>...
ma******@t-online.de (Math55) wrote:
hi, i have this piece of code:

---


[code snipped]
---

it prints the data that comes from the ttyS0 port. now i have 2
questions:

1. can it be that this code does not get all data from the port and


The code is copied from the Linux Serial-Programming-HOWTO,
(Section 3.1, Canonical Input Processing) which does indeed
work, but is perhaps not the best example of programming ever
distributed.
2. anyone good at decoding such signals?


There are several people who would be quite happy to go through
that example line by line and make comments, additions,
corrections, but not in comp.lang.c.

Please repost your query to an appropriate Linux related
newsgroup (try comp.os.linux.development.apps, for example), and
I'm quite sure you'll get a great deal of help. (I have a
complete set of replacement programs for each section in the
HOWTO. I understand that at least one other person has also
rewritten the entire document. Hence the potential for detailed
help is high.)
THANKS:)

would you send me the replacement programs? this would be nice:-)
please send to ni*********@t-online.de
THANKS A LOT, will try another group now.
Nov 13 '05 #4

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