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write() to /dev/ttyS0 has no effect
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write() to /dev/ttyS0 has no effect
by Borge
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Hi,
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? 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 */ #define FALSE 0 #define TRUE 1 FILE *keyboard; int status; main() { int fd,c, res; struct termios oldtio,newtio; keyboard = fopen("/dev/tty", "r"); //open the terminal keyboard if (!keyboard) { fprintf(stderr, "Unable to open /dev/tty\n"); exit(1); } fd = open(MODEMDEVICE, O_RDWR | O_NOCTTY ); if (fd <0) {perror(MODEMDEVICE); exit(-1); } fcntl(fd, F_SETFL, 0); // Needed??? tcgetattr(fd,&oldtio); // Save current port settings // Non-canonical init. bzero(&newtio, sizeof(newtio)); newtio.c_cflag = BAUDRATE | CRTSCTS | CS8 | CLOCAL | CREAD; newtio.c_iflag = IGNPAR; newtio.c_oflag = 0; newtio.c_lflag = 0; newtio.c_cc[VTIME] = 0; // inter-character timer unused newtio.c_cc[VMIN] = 5; // blocking read until 5 chars received tcflush(fd, TCIFLUSH); tcsetattr(fd,TCSANOW,&newtio); while (1) { status = getc(stdin); if (status == 'a') { char outbuf[] = "f"; printf("%s", outbuf); // This printout is ok write(fd, outbuf, 1); // This doesn't seem to get sent down the uart! } } tcsetattr(fd,TCSANOW,&oldtio); // Restore port settings } -- Problem reports: http://cygwin.com/problems.html FAQ: http://cygwin.com/faq/ Documentation: http://cygwin.com/docs.html Unsubscribe info: http://cygwin.com/ml/#unsubscribe-simple |
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Re: write() to /dev/ttyS0 has no effect
by Bugzilla from matthias.andree@gmx.de
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Børge 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() > { > int fd,c, res; > struct termios oldtio,newtio; > > keyboard = fopen("/dev/tty", "r"); //open the terminal keyboard What's that good for? You're not using that. > if (!keyboard) > { > fprintf(stderr, "Unable to open /dev/tty\n"); > exit(1); > } > > fd = open(MODEMDEVICE, O_RDWR | O_NOCTTY ); > if (fd <0) {perror(MODEMDEVICE); exit(-1); } > > fcntl(fd, F_SETFL, 0); // Needed??? Not needed. > > tcgetattr(fd,&oldtio); // Save current port settings > > // Non-canonical init. > bzero(&newtio, sizeof(newtio)); bzero() isn't standard. Use memset(), sample below. > newtio.c_cflag = BAUDRATE | CRTSCTS | CS8 | CLOCAL | CREAD; Does the µC support CRTSCTS? If not, that's why it fails. Also, BAUDRATE may not fit into speed_t according to /usr/include/sys/termios.h, so you're losing the "extended baud rate" flag and are actually programming 75 Baud instead of 115200. Use cfsetXspeed (X is i or o) to manipulate newtio instead, example (in C++): struct termios newtio; /* configure serial interface to 57600 8N1 no-canonical */ memset(&newtio, 0, sizeof(newtio)); newtio.c_cflag = CS8 | CLOCAL | CREAD; newtio.c_iflag = 0; newtio.c_oflag = 0; newtio.c_lflag = 0; newtio.c_cc[VTIME] = 0; newtio.c_cc[VMIN] = 1; /* at least 1 characters */ if (cfsetispeed(&newtio, B57600)) throw("cfsetispeed"); if (cfsetospeed(&newtio, B57600)) throw("cfsetospeed"); if (tcflush(fd, TCIFLUSH)) throw("tcflush"); if (tcsetattr(fd, TCSANOW, &newtio)) throw("tcsetattr"); > newtio.c_iflag = IGNPAR; > newtio.c_oflag = 0; > newtio.c_lflag = 0; > newtio.c_cc[VTIME] = 0; // inter-character timer unused > newtio.c_cc[VMIN] = 5; // blocking read until 5 chars received > > tcflush(fd, TCIFLUSH); > tcsetattr(fd,TCSANOW,&newtio); > > while (1) > { > status = getc(stdin); > if (status == 'a') { > char outbuf[] = "f"; > printf("%s", outbuf); // This printout is ok > write(fd, outbuf, 1); // This doesn't seem to get sent down the uart! > } > > } You're apparently not reading from the serial line. Is that intentional? > tcsetattr(fd,TCSANOW,&oldtio); // Restore port settings This is unreached (dead) code. > } HTH -- Problem reports: http://cygwin.com/problems.html FAQ: http://cygwin.com/faq/ Documentation: http://cygwin.com/docs.html Unsubscribe info: http://cygwin.com/ml/#unsubscribe-simple |
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Re: write() to /dev/ttyS0 has no effect
by Borge
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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 = 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. Børge On Thu, Oct 29, 2009 at 10:59, Matthias Andree <matthias.andree@...> wrote: > Børge 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() >> { >> int fd,c, res; >> struct termios oldtio,newtio; >> >> keyboard = fopen("/dev/tty", "r"); //open the terminal keyboard > > What's that good for? You're not using that. > >> if (!keyboard) >> { >> fprintf(stderr, "Unable to open /dev/tty\n"); >> exit(1); >> } >> >> fd = open(MODEMDEVICE, O_RDWR | O_NOCTTY ); >> if (fd <0) {perror(MODEMDEVICE); exit(-1); } >> >> fcntl(fd, F_SETFL, 0); // Needed??? > > Not needed. > >> >> tcgetattr(fd,&oldtio); // Save current port settings >> >> // Non-canonical init. >> bzero(&newtio, sizeof(newtio)); > > bzero() isn't standard. Use memset(), sample below. > >> newtio.c_cflag = BAUDRATE | CRTSCTS | CS8 | CLOCAL | CREAD; > > Does the µC support CRTSCTS? If not, that's why it fails. > > Also, BAUDRATE may not fit into speed_t according to /usr/include/sys/termios.h, > so you're losing the "extended baud rate" flag and are actually programming 75 > Baud instead of 115200. Use cfsetXspeed (X is i or o) to manipulate newtio > instead, example (in C++): > > struct termios newtio; > /* configure serial interface to 57600 8N1 no-canonical */ > memset(&newtio, 0, sizeof(newtio)); > newtio.c_cflag = CS8 | CLOCAL | CREAD; > newtio.c_iflag = 0; > newtio.c_oflag = 0; > newtio.c_lflag = 0; > newtio.c_cc[VTIME] = 0; > newtio.c_cc[VMIN] = 1; /* at least 1 characters */ > if (cfsetispeed(&newtio, B57600)) throw("cfsetispeed"); > if (cfsetospeed(&newtio, B57600)) throw("cfsetospeed"); > if (tcflush(fd, TCIFLUSH)) throw("tcflush"); > if (tcsetattr(fd, TCSANOW, &newtio)) throw("tcsetattr"); > > >> newtio.c_iflag = IGNPAR; >> newtio.c_oflag = 0; >> newtio.c_lflag = 0; >> newtio.c_cc[VTIME] = 0; // inter-character timer unused >> newtio.c_cc[VMIN] = 5; // blocking read until 5 chars received >> >> tcflush(fd, TCIFLUSH); >> tcsetattr(fd,TCSANOW,&newtio); >> >> while (1) >> { >> status = getc(stdin); >> if (status == 'a') { >> char outbuf[] = "f"; >> printf("%s", outbuf); // This printout is ok >> write(fd, outbuf, 1); // This doesn't seem to get sent down the uart! >> } >> >> } > > You're apparently not reading from the serial line. Is that intentional? > >> tcsetattr(fd,TCSANOW,&oldtio); // Restore port settings > > This is unreached (dead) code. > >> } > > HTH > > -- > Problem reports: http://cygwin.com/problems.html > FAQ: http://cygwin.com/faq/ > Documentation: http://cygwin.com/docs.html > Unsubscribe info: http://cygwin.com/ml/#unsubscribe-simple > > -- Problem reports: http://cygwin.com/problems.html FAQ: http://cygwin.com/faq/ Documentation: http://cygwin.com/docs.html Unsubscribe info: http://cygwin.com/ml/#unsubscribe-simple |
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