Wrong order of bytes received from serial port - c

Question

I have a device with FPGA which sends data via simple UART. The data is a packet of 32 bytes, baudrate is 115200. I connect them to my laptop via UART-TTL/USB adapter, so in system (Ubuntu 14.04) I can read the data from ttyUSB. I've made a simple application in GTK/C to receive the data, make some math and save results in text file. Everything was working fine until I increased frequency of sending 32 bytes packets from 5 times per second to 100 times per second. The problem is one packet in a dozen or several dozen has wrong order of bytes. I've checked with logic analyzer that my FPGA sends data correctly every time.
For example, FPGA sends packet:
1 2 3 4 5 6 7 8 9
But my application sometimes receives:
1 2 7 3 4 5 6 8 9
I'm using this function to open serial port:
int rs232_open(char *com_name, int baudrate, int databits, char *parity, int stopbits)
{
serial_fd = open(com_name, O_RDWR | O_NOCTTY | O_NDELAY); //open port
if(serial_fd==-1)
{
perror("unable to open comport ");
return 1;
}
error = tcgetattr(serial_fd, &old_settings); //save actual port settings
if(error==-1)
{
close(serial_fd);
perror("unable to read portsettings ");
return 2;
}
memset(&new_settings, 0, sizeof(new_settings));
new_settings.c_iflag = 0; //without in processing
new_settings.c_oflag = 0; //without out processing
new_settings.c_lflag = 0; //without line processing
new_settings.c_cflag = CLOCAL | CREAD; //without flow control, receiver active
switch(baudrate) //baudrate
{
case 9600: new_settings.c_cflag |= B9600; break;
case 19200: new_settings.c_cflag |= B19200; break;
case 38400: new_settings.c_cflag |= B38400; break;
case 115200: new_settings.c_cflag |= B115200; break;
default: return 3; break;
}
switch(databits) //number of data bits
{
case 5: new_settings.c_cflag |= CS5; break;
case 6: new_settings.c_cflag |= CS6; break;
case 7: new_settings.c_cflag |= CS7; break;
case 8: new_settings.c_cflag |= CS8; break;
default: return 3;
}
switch(parity[0]) //parity
{
case 'N': new_settings.c_iflag |= IGNPAR; break;
case 'E': new_settings.c_cflag |= PARENB; break;
case 'O': new_settings.c_cflag |= PARENB | PARODD; break;
default: return 3;
}
switch (stopbits) //stop bits
{
case 1: break; //1 bit
case 2: new_settings.c_cflag |= CSTOPB; break; //2 bits
default: return 3;
}
new_settings.c_cc[VMIN] = 1; //1 received char allows to read
new_settings.c_cc[VTIME] = 0;
tcflush(serial_fd, TCIOFLUSH); //clear port buffers
error = tcsetattr(serial_fd, TCSANOW, &new_settings); //save new settings
if(error==-1)
{
close(serial_fd);
perror("unable to set portsettings ");
return 4;
}
return 0;
}
In my GTK/C application clicking on the "OPEN" button calls above function:
rs232_open("ttyUSB0",115200,8,"N",2);
Then, I create a channel for serial port, set its coding and add a handler for receive event:
int serial_fd; //serial port file descriptor
GIOChannel *serial_ch; //serial port channel
serial_ch = g_io_channel_unix_new(serial_fd); //attach channel to serial port
g_io_add_watch(serial_ch, G_IO_IN, read_channel, NULL); //attach read_channel handler function
Function read_channel() looks like this (frame is a struct with table of chars buffer and integer field byte_number):
gboolean read_channel(GIOChannel *channel, GIOCondition condition, gpointer data)
{
unsigned char i;
gsize bytes_read;
gchar chr;
GString *recdata = g_string_new(NULL);
if(g_io_channel_read_chars(channel, &chr, 1, &bytes_read, NULL) == G_IO_STATUS_NORMAL) //if reading a byte is successful
{
if(bytes_read) //1 byte received
{
//
// here I search for 0x55 0x55 sequence (start tag of 32 bytes packet)
// if start tag is received frame buffer is cleared and byte counter zeroed
//
frame.buffer[frame.byte_number++]=chr; //save received byte to buffer
if(frame.byte_number > BUFFER_SIZE-1) //frame buffer full
{
if(frame.buffer[BUFFER_SIZE-1] == 0x0D) //end tag is correct (0x0D is end tag of my 32 bytes packet)
{
//
// here I convert received data (some int16 numbers)
// and save them in readable form to text file
// also as a string of hex numbers for debugging
//
}
else //end tag not correct
{
//
// here I increase error counter
//
}
for(i=0; i<BUFFER_SIZE; i++) frame.buffer[i]=0; //clear the buffer
frame.byte_number=0; //reset byte counter
}
}
}
return TRUE;
}