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POIssues writing to serial port on MAC OSX using unistd.h in c
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copied!<p>I am trying to write to a bluetooth device on MAC OSX using the unistd.h Linux functions in c. I am connecting fine and writing the first few bytes with success. When I try to write other commands to it (there are bytes added to the write buffer every 15ms), I don't see any results even though the write() function returns 1 (write success).</p> <p>If you start a write and it doesn't finish by the time you try to start another write (since it is non-blocking), could that possibly screw up the initial write? (If so, is there any way to check if a write has completed?) That is the only thing I can think of since the writes are occurring fairly frequently and the first two are successfully sent.</p> <p>qwbyte() simply adds a byte to the output array and increments its length</p> <p>The open port function:</p> <pre><code>BAMid = -1; struct termios options; struct termios originalTTYAttrs; // Open the serial port read/write, nonblocking, with no controlling terminal, and don't wait for a connection. BAMid = open(strPath, O_RDWR | O_NOCTTY | O_NONBLOCK); if (BAMid == -1) { printf("Error opening serial port %s - %s(%d).\n", strPath, strerror(errno), errno); goto error; } // Issue TIOCEXCL ioctl to prevent additional opens except by root-owned processes. if (ioctl(BAMid, TIOCEXCL) == -1) { printf("Error setting TIOCEXCL on %s - %s(%d).\n", strPath, strerror(errno), errno); goto error; } // Get the current options and save them so we can restore the default settings later. if (tcgetattr(BAMid, &originalTTYAttrs) == -1) { printf("Error getting tty attributes %s - %s(%d).\n", strPath, strerror(errno), errno); goto error; } // The serial port attributes such as timeouts and baud rate are set by modifying the termios // structure and then calling tcsetattr() to cause the changes to take effect. Note that the // changes will not become effective without the tcsetattr() call. options = originalTTYAttrs; // Set raw input (non-canonical) mode, with reads blocking until either a single character // has been received or a one second timeout expires. [should be moot since we are leaving it as nonblocking] cfmakeraw(&options); options.c_cc[VMIN] = 1; options.c_cc[VTIME] = 10; cfsetspeed(&options, B57600); // Set 57600 baud options.c_cflag |= CS8; // Use 8 bit words // Cause the new options to take effect immediately. if (tcsetattr(BAMid, TCSANOW, &options) == -1) { printf("Error setting tty attributes %s - %s(%d).\n", strPath, strerror(errno), errno); goto error; } //flush old transmissions if (tcflush(BAMid,TCIOFLUSH) == -1) { printf("Error flushing BAM serial port - %s(%d).\n", strerror(errno), errno); } oBufLength = 0; // Ask it to start if (! qwbyte(CmdStart) ) { goto error; } if (! qwbyte(CmdFull) ) { goto error; } //this transmit works txbytes(); printf("success opening port!"); return -1; // Failure path error: if (BAMid != -1) { close(BAMid); } printf("returning an error--%d",errno); return errno; } </code></pre> <p>The write function (txbytes):</p> <pre><code>int i, bufSize, numBytes; if(oBufLength != 0) { //if the output array isn't empty //duplicating the output array and its size so it can //be overwritten while this write is occuring printf("about to transmit: "); for(i = 0; i < oBufLength; i++) { printf(" %u",oBuf[i]); tempBuf[i] = oBuf[i]; } printf("\n"); bufSize = oBufLength; oBufLength = 0; numBytes = write(BAMid, &tempBuf, bufSize); printf("bytes written = %d\n",numBytes); if (numBytes == -1) { printf("Error writing to port - %s(%d).\n", strerror(errno), errno); } return (numBytes > 0); } else { return 0; } </code></pre>

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