Linux C Read GPS Data From UART

Linux C Read GPS data from UART

1.使用Terminal終端機介面(TTY)，讓Linux系統透過UART串列埠連接GPS。終端機介面有二種模式：正規(canonical)模式和非正規(non-canonical=raw input)模式。
模式 說明

• 正規(canonical)模式: 終端設備會處理特殊字元，且會以一次一列的方式將輸入傳給應用程式。

正規模式	原文
Canonical Input	Canonical input is line-oriented. Input characters are put into a buffer which can be edited interactively by the user until a CR (carriage return) or LF (line feed) character is received.  When selecting this mode you normally select the ICANON, ECHO, and ECHOE options:  options.c_lflag |= (ICANON | ECHO | ECHOE);

• 非正規(non-canonical)模式:又稱為raw模式。在這種模式中，終端設備不會處理特殊字元，且會以一次一個字元的方式將輸入傳給應用程式。　 　 　 　 　 　

非正規	原文
Raw Input	Raw input is unprocessed. Input characters are passed through exactly as they are received, when they are received. Generally you'll deselect the ICANON, ECHO, ECHOE, and ISIG options when using raw input:  options.c_lflag &= ~(ICANON | ECHO | ECHOE | ISIG);

2.開啟通訊埠

#include <sys/types.h> #include <sys/stat.h> #include <fcntl.h> #include <termios.h> #include <stdio.h> #define MODEMDEVICE "/dev/ttyS2" ... fd = open(MODEMDEVICE, O_RDWR|O_NOCTTY|O_NDELAY ); if (fd <0) {perror(MODEMDEVICE); exit(-1); } ...

3.Termios結構　 　 　

struct termios{ tcflag_t c_iflag;                    /*輸入模式*/ tcflag_t c_oflag;                   /*輸出模式*/ tcflag_t c_cflag;                   /*控制模式*/ tcflag_t c_lflag;                    /*局部模式*/ cc_t c_cc[NCCS];               /*特殊控制字元*/ }

Table : The c_iflag Member

Constant	Description
INPCK	Enable parity check
IGNPAR	Ignore parity errors
PARMRK	Mark parity errors
ISTRIP	Strip parity bits
IXON	Enable software flow control (outgoing)
IXOFF	Enable software flow control (incoming)
IXANY	Allow any character to start flow again
IGNBRK	Ignore break condition
BRKINT	Send a SIGINT when a break condition is detected
INLCR	Map NL to CR
IGNCR	Ignore CR
ICRNL	Map CR to NL
IUCLC	Map uppercase to lowercase
IMAXBEL	Echo BEL on input line too long

Table : The c_oflag Member

Constant	Description
OPOST	Postprocess output (not set = raw output)
OLCUC	Map lowercase to uppercase
ONLCR	Map NL to CR-NL
OCRNL	Map CR to NL
NOCR	No CR output at column 0
ONLRET	NL performs CR function
OFILL	Use fill characters for delay
OFDEL	Fill character is DEL
NLDLY	Mask for delay time needed between lines
NL0	No delay for NLs
NL1	Delay further output after newline for 100 milliseconds
CRDLY	Mask for delay time needed to return carriage to left column
CR0	No delay for CRs
CR1	Delay after CRs depending on current column position
CR2	Delay 100 milliseconds after sending CRs
CR3	Delay 150 milliseconds after sending CRs
TABDLY	Mask for delay time needed after TABs
TAB0	No delay for TABs
TAB1	Delay after TABs depending on current column position
TAB2	Delay 100 milliseconds after sending TABs
TAB3	Expand TAB characters to spaces
BSDLY	Mask for delay time needed after BSs
BS0	No delay for BSs
BS1	Delay 50 milliseconds after sending BSs
VTDLY	Mask for delay time needed after VTs
VT0	No delay for VTs
VT1	Delay 2 seconds after sending VTs
FFDLY	Mask for delay time needed after FFs
FF0	No delay for FFs
FF1	Delay 2 seconds after sending FFs

Table : The c_cc Member

Constant	Description	Key
VINTR	Interrupt	CTRL-C
VQUIT	Quit	CTRL-Z
VERASE	Erase	Backspace (BS)
VKILL	Kill-line	CTRL-U
VEOF	End-of-file	CTRL-D
VEOL	End-of-line	Carriage return (CR)
VEOL2	Second end-of-line	Line feed (LF)
VMIN	Minimum number of characters to read
VTIME	Time to wait for data (tenths of seconds)

4.範例

4.1

Canonical Input Processing

#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/ttyS2" #define _POSIX_SOURCE 1 /* POSIX compliant source */ #define FALSE 0 #define TRUE 1 volatile int STOP=FALSE; int main(int argc, char *argv[]) { 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); } close(fd); return 0; }

4.2

Non-Canonical Input Processing

#include <sys/types.h> #include <sys/stat.h> #include <fcntl.h> #include <termios.h> #include <stdio.h> #define BAUDRATE B38400 #define MODEMDEVICE "/dev/ttyS2" #define _POSIX_SOURCE 1 /* POSIX compliant source */ #define FALSE 0 #define TRUE 1 volatile int STOP=FALSE; int main(int argc, char *argv[]) { int fd,c, res; struct termios oldtio,newtio; char buf[255]; fd = open(MODEMDEVICE, O_RDWR | O_NOCTTY ); if (fd <0) {perror(MODEMDEVICE); exit(-1); } tcgetattr(fd,&oldtio); /* save current port settings */ bzero(&newtio, sizeof(newtio)); newtio.c_cflag = BAUDRATE | CRTSCTS | CS8 | CLOCAL | CREAD; newtio.c_iflag = IGNPAR; newtio.c_oflag = 0; /* set input mode (non-canonical, no echo,...) */ newtio.c_lflag = 0; newtio.c_cc[VTIME] = 0; /* inter-character timer unused */ newtio.c_cc[VMIN] = 1; /* blocking read until 5 chars received */ tcflush(fd, TCIFLUSH); tcsetattr(fd,TCSANOW,&newtio); while (STOP==FALSE) { /* loop for input */ res = read(fd,buf,255); /* returns after 5 chars have been input */ buf[res]=0; /* so we can printf... */ printf(":%s:%d\n", buf, res); if (buf[0]=='z') STOP=TRUE; } tcsetattr(fd,TCSANOW,&oldtio); close(fd); return 0; }//main

4.3

Asynchronous Input

#include <termios.h> #include <stdio.h> #include <unistd.h> #include <fcntl.h> #include <sys/signal.h> #include <sys/types.h> #define BAUDRATE B38400 #define MODEMDEVICE "/dev/ttyS1" #define _POSIX_SOURCE 1 /* POSIX compliant source */ #define FALSE 0 #define TRUE 1 volatile int STOP=FALSE; void signal_handler_IO (int status); /* definition of signal handler */ int wait_flag=TRUE; /* TRUE while no signal received */ int main(int argc, char *argv[]) { int fd,c, res; struct termios oldtio,newtio; struct sigaction saio; /* definition of signal action */ char buf[255]; /* open the device to be non-blocking (read will return immediatly) */ fd = open(MODEMDEVICE, O_RDWR | O_NOCTTY | O_NONBLOCK); if (fd <0) {perror(MODEMDEVICE); exit(-1); } /* install the signal handler before making the device asynchronous */ saio.sa_handler = signal_handler_IO; saio.sa_mask = 0; saio.sa_flags = 0; saio.sa_restorer = NULL; sigaction(SIGIO,&saio,NULL); /* allow the process to receive SIGIO */ fcntl(fd, F_SETOWN, getpid()); /* Make the file descriptor asynchronous (the manual page says only O_APPEND and O_NONBLOCK, will work with F_SETFL...) */ fcntl(fd, F_SETFL, FASYNC); tcgetattr(fd,&oldtio); /* save current port settings */ /* set new port settings for canonical input processing */ newtio.c_cflag = BAUDRATE | CRTSCTS | CS8 | CLOCAL | CREAD; newtio.c_iflag = IGNPAR | ICRNL; newtio.c_oflag = 0; newtio.c_lflag = ICANON; newtio.c_cc[VMIN]=1; newtio.c_cc[VTIME]=0; tcflush(fd, TCIFLUSH); tcsetattr(fd,TCSANOW,&newtio); /* loop while waiting for input. normally we would do something useful here */ while (STOP==FALSE) { printf(".\n");usleep(100000); /* after receiving SIGIO, wait_flag = FALSE, input is available and can be read */ if (wait_flag==FALSE) { res = read(fd,buf,255); buf[res]=0; printf(":%s:%d\n", buf, res); if (res==1) STOP=TRUE; /* stop loop if only a CR was input */ wait_flag = TRUE; /* wait for new input */ } } /* restore old port settings */ tcsetattr(fd,TCSANOW,&oldtio); close(fd); return 0; } /*************************************************************************** * signal handler. sets wait_flag to FALSE, to indicate above loop that * * characters have been received. * ***************************************************************************/ void signal_handler_IO (int status) { printf("received SIGIO signal.\n"); wait_flag = FALSE; }

4.4

Waiting for Input from Multiple Sources

#include <sys/time.h> #include <sys/types.h> #include <unistd.h> int main(int argc, char *argv[]) { int fd1, fd2; /* input sources 1 and 2 */ fd_set readfs; /* file descriptor set */ int maxfd; /* maximum file desciptor used */ int loop=1; /* loop while TRUE */ /* open_input_source opens a device, sets the port correctly, and returns a file descriptor */ fd1 = open_input_source("/dev/ttyS1"); /* COM2 */ if (fd1<0) exit(0); fd2 = open_input_source("/dev/ttyS2"); /* COM3 */ if (fd2<0) exit(0); maxfd = MAX (fd1, fd2)+1; /* maximum bit entry (fd) to test */ /* loop for input */ while (loop) { FD_SET(fd1, &readfs); /* set testing for source 1 */ FD_SET(fd2, &readfs); /* set testing for source 2 */ /* block until input becomes available */ select(maxfd, &readfs, NULL, NULL, NULL); if (FD_ISSET(fd1)) /* input from source 1 available */ handle_input_from_source1(); if (FD_ISSET(fd2)) /* input from source 2 available */ handle_input_from_source2(); } close(fd1); close(fd2); return 0; }

The given example blocks indefinitely, until input from one of the sources becomes available. If you need to timeout on input, just replace the select call by:

int res; struct timeval Timeout; /* set timeout value within input loop */ Timeout.tv_usec = 0; /* milliseconds */ Timeout.tv_sec = 1; /* seconds */ res = select(maxfd, &readfs, NULL, NULL, &Timeout); if (res==0) /* number of file descriptors with input = 0, timeout occurred. */

[參考]
1.http://blog.xuite.net/uwlib_mud/twblog/108242774-Linux+RS-232+程式設計
2.https://www.cmrr.umn.edu/~strupp/serial.html.
3.http://www.tldp.org/HOWTO/Serial-Programming-HOWTO/x115.html