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From: =?ISO-8859-1?Q?B=F8rge_Strand=2DBergesen?= <borge DOT strand AT gmail DOT com>
Date: Thu, 29 Oct 2009 12:05:33 +0100
Message-ID: <187469a20910290405o6091b108u58856ee06ea98c98@mail.gmail.com>
Subject: Re: write() to /dev/ttyS0 has no effect
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Matthias,

vielen Dank!

It works now. Your questions were mostly about unrelated code that
somehow survived as I stripped things down to make the example.
Removing CRTSCTS did the trick.

I see that you are using non-canonical reads. Do you know if canonical
works on Cygwin? In my finished program I will indeed be reading input
from the UART. But "res =3D read(fd,inbuf,255);" returns on several
occations when it contents are not terminated by \n, \r or 0. As you
probably see from my code, I have copied the Serial HOWTO code.


B=F8rge


On Thu, Oct 29, 2009 at 10:59, Matthias Andree <matthias DOT andree AT gmx DOT de> wro=
te:
> B=F8rge Strand-Bergesen schrieb:
>
>> I'm writing some C code to control an external MCU over UART.
>> Everything works like a charm using TeraTerm or cat >>/dev/ttyS0. gcc
>> is 3.4.4. In a different program (not inserted), I am able to use
>> read() to get information from the MCU. Cygwin is "CYGWIN_NT-5.1
>> 1.5.25(0.156/4/2) 2008-06-12 19:34".
>>
>> However, it seems like no information is sent when I call write(). Are
>> there any known bugs with Cygwin when it comes to this?
>
> "Works for me", albeit with MSP430 behind a FTDI USB/serial converter and
> without CRTSCTS and lower bit rate (57600).
>
>> I have inserted my code below. Thanks for any help!
>>
>> "f" is a valid command to the MCU. The MCU will disregard any \r or
>> \n. I have tried hitting the enter button, not just 'a' on the
>> keyboard.
>>
>>
>> Borge
>>
>>
>> #include <sys/types.h>
>> #include <sys/stat.h>
>> #include <fcntl.h>
>> #include <termios.h>
>> #include <stdio.h>
>> #include <string.h>
>>
>> #define BAUDRATE B115200
>> #define MODEMDEVICE "/dev/ttyS0"
>> #define _POSIX_SOURCE 1 /* POSIX compliant source */
>
> This must be before the first #include.
>
>> #define FALSE 0
>> #define TRUE 1
>>
>>
>> FILE *keyboard;
>> int status;
>>
>> main()
>> {
>> =A0 =A0 =A0 int fd,c, res;
>> =A0 =A0 =A0 struct termios oldtio,newtio;
>>
>> =A0 =A0 =A0 keyboard =3D fopen("/dev/tty", "r"); =A0 =A0 =A0//open the t=
erminal keyboard
>
> What's that good for? You're not using that.
>
>> =A0 =A0 =A0 if (!keyboard)
>> =A0 =A0 =A0 {
>> =A0 =A0 =A0 =A0 =A0 =A0 =A0 fprintf(stderr, "Unable to open /dev/tty\n");
>> =A0 =A0 =A0 =A0 =A0 =A0 =A0 exit(1);
>> =A0 =A0 =A0 }
>>
>> =A0 =A0 =A0 fd =3D open(MODEMDEVICE, O_RDWR | O_NOCTTY );
>> =A0 =A0 =A0 if (fd <0) {perror(MODEMDEVICE); exit(-1); }
>>
>> =A0 =A0 =A0 fcntl(fd, F_SETFL, 0); // Needed???
>
> Not needed.
>
>>
>> =A0 =A0 =A0 tcgetattr(fd,&oldtio); =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =
=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0// Save current port settings
>>
>> =A0 =A0 =A0 // Non-canonical init.
>> =A0 =A0 =A0 bzero(&newtio, sizeof(newtio));
>
> bzero() isn't standard. Use memset(), sample below.
>
>> =A0 =A0 =A0 newtio.c_cflag =3D BAUDRATE | CRTSCTS | CS8 | CLOCAL | CREAD;
>
> Does the =B5C support CRTSCTS? If not, that's why it fails.
>
> Also, BAUDRATE may not fit into speed_t according to /usr/include/sys/ter=
mios.h,
> so you're losing the "extended baud rate" flag and are actually programmi=
ng 75
> Baud instead of 115200. Use cfsetXspeed (X is i or o) to manipulate newtio
> instead, example (in C++):
>
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0struct termios newtio;
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0/* configure serial interface to 57600 8N1=
 no-canonical */
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0memset(&newtio, 0, sizeof(newtio));
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0newtio.c_cflag =3D CS8 | CLOCAL | CREAD;
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0newtio.c_iflag =3D 0;
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0newtio.c_oflag =3D 0;
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0newtio.c_lflag =3D 0;
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0newtio.c_cc[VTIME] =3D 0;
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0newtio.c_cc[VMIN] =3D 1; =A0/* at least 1 =
characters */
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0if (cfsetispeed(&newtio, B57600)) throw("c=
fsetispeed");
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0if (cfsetospeed(&newtio, B57600)) throw("c=
fsetospeed");
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0if (tcflush(fd, TCIFLUSH)) throw("tcflush"=
);
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0if (tcsetattr(fd, TCSANOW, &newtio)) throw=
("tcsetattr");
>
>
>> =A0 =A0 =A0 newtio.c_iflag =3D IGNPAR;
>> =A0 =A0 =A0 newtio.c_oflag =3D 0;
>> =A0 =A0 =A0 newtio.c_lflag =3D 0;
>> =A0 =A0 =A0 newtio.c_cc[VTIME] =3D 0; =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =
=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 // inter-character timer unused
>> =A0 =A0 =A0 newtio.c_cc[VMIN] =3D 5; =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0=
 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0// blocking read until 5 chars received
>>
>> =A0 =A0 =A0 tcflush(fd, TCIFLUSH);
>> =A0 =A0 =A0 tcsetattr(fd,TCSANOW,&newtio);
>>
>> =A0 =A0 =A0 while (1)
>> =A0 =A0 =A0 {
>> =A0 =A0 =A0 =A0 =A0 =A0 =A0 status =3D getc(stdin);
>> =A0 =A0 =A0 =A0 =A0 =A0 =A0 if (status =3D=3D 'a') {
>> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 char outbuf[] =3D "f";
>> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 printf("%s", outbuf); =A0 =
=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 // This printout is ok
>> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 write(fd, outbuf, 1); =A0 =
=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 // This doesn't seem to get sent down the u=
art!
>> =A0 =A0 =A0 =A0 =A0 =A0 =A0 }
>>
>> =A0 =A0 =A0 }
>
> You're apparently not reading from the serial line. Is that intentional?
>
>> =A0 =A0 =A0 tcsetattr(fd,TCSANOW,&oldtio); =A0 =A0 =A0 =A0 =A0 =A0 =A0 =
=A0 =A0// Restore port settings
>
> This is unreached (dead) code.
>
>> }
>
> HTH
>
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