Issues writing to serial port on MAC OSX using unistd.h in c
- by Schuyler
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).
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.
qwbyte() simply adds a byte to the output array and increments its length
The open port function:
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;
}
The write function (txbytes):
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;
}
