Program hangs when setting serial port parameters - c

Question

In my program a connection is opened with serial port that recieves 10-byte packages with set frequency (usually 100 Hz). However i have run into the following problem: sometimes (but not always) when i am closing connection, the program hangs.
In the following code i do not specify constants; at runtime connection parameters (baud rate, parity...) are determined from command line. In practice, connection is usually opened with baud rate 230400, no parity, 8-bit character size and 1 stop bit.
This is how i am opening serial port:
struct termios config;
LOGPRINT("Will operate on device \'%s\'\n", pconfig->device);
LOGPRINT("Opening serial device\n");
int flag = O_RDWR | O_NOCTTY | ASYNC_LOW_LATENCY;
// pconfig contains some necessary information to set connection parameters
// async == false for connectin that causes problems
int fd = open(pconfig->device, async? flag | O_NONBLOCK: flag);
if(fd == -1)
{ /* skipped error handling */ }
LOGPRINT("Retrieving terminal attributes\n");
if(!!tcgetattr(fd, &config))
{ /* skipped error handling */ }
else
{
// backup old configuration for restoring it on exit
if(poldconfig != NULL)
memcpy(poldconfig, &config, sizeof(struct termios));
LOGPRINT("Setting terminal attributes\n");
set_attribs(fd, &config, pconfig);
}
...
int set_attribs(const int fd, struct termios* pterm, const struct serial_config* pconfig)
{
// set baud rate
// baud_rates contains integers of actual rates
LOGPRINT("Setting baud rate to %d.\n", baud_rates[pconfig->baud_rate_index]);
// change to raw mode
LOGPRINT("Setting terminal to raw mode\n");
pterm->c_iflag &= ~(IGNBRK | BRKINT | PARMRK | ISTRIP | INLCR
| IGNCR | ICRNL | IXON);
pterm->c_oflag &= OPOST;
pterm->c_lflag &= ~(ECHO | ECHONL | ICANON | ISIG | IEXTEN);
// baud_bits contains actual pre-defined baud rate flags
cfsetispeed(pterm, baud_bits[pconfig->baud_rate_index]);
cfsetospeed(pterm, baud_bits[pconfig->baud_rate_index]);
LOGPRINT("Set character size, parity and stop bit flags.\n");
// set character size
pterm->c_cflag &= ~CSIZE;
pterm->c_cflag |= pconfig->csize_flag;
// set parity
pterm->c_cflag &= ~(PARENB | PARODD);
pterm->c_cflag |= pconfig->parity_flag;
// set stopbits
pterm->c_cflag &= ~CSTOPB;
pterm->c_cflag |= pconfig->stopbits_flag;
// enable reading; ignore control lines
pterm->c_cflag |= CREAD | CLOCAL;
LOGPRINT("Flush terminal.\n");
// flush terminal
tcflush(fd, TCIOFLUSH);
LOGPRINT("Apply parameters.\n");
return tcsetattr(fd, TCSANOW, pterm);
}
For valid reasons, i needed to force serial device driver to use 1-byte buffer for incoming/outgoing data, which i have set using this function:
int set_port_type(int fd, int ptype)
{
struct serial_struct temp;
int res = ioctl(fd, TIOCGSERIAL, &temp);
if(!!res)
{ /* stipped error handling */ }
temp.type = ptype;
res = ioctl(fd, TIOCSSERIAL, &temp);
if(!!res)
{ /* stipped error handling */ }
return res;
}
with ptype = PORT_UNKNOWN or ptype = PORT_16450.
When finished with serial port, i perform the following operations:
Flush it
Set its type back to 16550A
Restore its settigns to saved ones
Close it
From time to time it causes the program to hang and stop responding to any external stimulus. It forces me to suspend the program and then reboot system, as it never releases file descriptors it holds.
What can i do to ensure that does not happen? Even if settings are not restored, the program needs to close on its own - maybe with error code.
Operating system i am using is TinyCore Linux. No other user program is being run an the same time as my program.
IMportant clarification. Serial device i am working with is actually NPort 5232 - asyncronous RS-422/485 - Ethernet communicator (description from vendor. Consequently, serial devices i am working with are virtual, which enables me to try and change their type / size of internal buffer.