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copied!<p>I wrote this a long time ago, and just copy and paste the bits needed into each project.</p> <pre><code>#include <errno.h> #include <fcntl.h> #include <string.h> #include <termios.h> #include <unistd.h> int set_interface_attribs (int fd, int speed, int parity) { struct termios tty; memset (&tty, 0, sizeof tty); if (tcgetattr (fd, &tty) != 0) { error_message ("error %d from tcgetattr", errno); return -1; } cfsetospeed (&tty, speed); cfsetispeed (&tty, speed); tty.c_cflag = (tty.c_cflag & ~CSIZE) | CS8; // 8-bit chars // disable IGNBRK for mismatched speed tests; otherwise receive break // as \000 chars tty.c_iflag &= ~IGNBRK; // disable break processing tty.c_lflag = 0; // no signaling chars, no echo, // no canonical processing tty.c_oflag = 0; // no remapping, no delays tty.c_cc[VMIN] = 0; // read doesn't block tty.c_cc[VTIME] = 5; // 0.5 seconds read timeout tty.c_iflag &= ~(IXON | IXOFF | IXANY); // shut off xon/xoff ctrl tty.c_cflag |= (CLOCAL | CREAD);// ignore modem controls, // enable reading tty.c_cflag &= ~(PARENB | PARODD); // shut off parity tty.c_cflag |= parity; tty.c_cflag &= ~CSTOPB; tty.c_cflag &= ~CRTSCTS; if (tcsetattr (fd, TCSANOW, &tty) != 0) { error_message ("error %d from tcsetattr", errno); return -1; } return 0; } void set_blocking (int fd, int should_block) { struct termios tty; memset (&tty, 0, sizeof tty); if (tcgetattr (fd, &tty) != 0) { error_message ("error %d from tggetattr", errno); return; } tty.c_cc[VMIN] = should_block ? 1 : 0; tty.c_cc[VTIME] = 5; // 0.5 seconds read timeout if (tcsetattr (fd, TCSANOW, &tty) != 0) error_message ("error %d setting term attributes", errno); } ... char *portname = "/dev/ttyUSB1" ... int fd = open (portname, O_RDWR | O_NOCTTY | O_SYNC); if (fd < 0) { error_message ("error %d opening %s: %s", errno, portname, strerror (errno)); return; } set_interface_attribs (fd, B115200, 0); // set speed to 115,200 bps, 8n1 (no parity) set_blocking (fd, 0); // set no blocking write (fd, "hello!\n", 7); // send 7 character greeting usleep ((7 + 25) * 100); // sleep enough to transmit the 7 plus // receive 25: approx 100 uS per char transmit char buf [100]; int n = read (fd, buf, sizeof buf); // read up to 100 characters if ready to read </code></pre> <p>The values for speed are <code>B115200</code>, <code>B230400</code>, <code>B9600</code>, <code>B19200</code>, <code>B38400</code>, <code>B57600</code>, <code>B1200</code>, <code>B2400</code>, <code>B4800</code>, etc. The values for parity are <code>0</code> (meaning no parity), <code>PARENB|PARODD</code> (enable parity and use odd), <code>PARENB</code> (enable parity and use even), <code>PARENB|PARODD|CMSPAR</code> (mark parity), and <code>PARENB|CMSPAR</code> (space parity).</p> <p>"Blocking" sets whether a <code>read()</code> on the port waits for the specified number of characters to arrive. Setting <em>no blocking</em> means that a <code>read()</code> returns however many characters are available without waiting for more, up to the buffer limit.</p> <hr> <p>Addendum:</p> <p><code>CMSPAR</code> is needed only for choosing mark and space parity, which is uncommon. For most applications, it can be omitted. My header file <code>/usr/include/bits/termios.h</code> enables definition of <code>CMSPAR</code> only if the preprocessor symbol <code>__USE_MISC</code> is defined. That definition occurs (in <code>features.h</code>) with</p> <pre><code>#if defined _BSD_SOURCE || defined _SVID_SOURCE #define __USE_MISC 1 #endif </code></pre> <p>The introductory comments of <code><features.h></code> says:</p> <pre><code>/* These are defined by the user (or the compiler) to specify the desired environment: ... _BSD_SOURCE ISO C, POSIX, and 4.3BSD things. _SVID_SOURCE ISO C, POSIX, and SVID things. ... */ </code></pre>

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