Read serial port with inter-character timeout for long streams - c

Question

in my application i am connected to serial device which will send periodic data whose size is unknown. I do not want to detect incoming frame using StartofFrame and EndOfFrame keywords. Instead of this, i want to detect incoming frame using inter-character timeout. There always will be some duration between incoming data frames at least 100ms.
So, i can detect frames using this time interval. I am opening serial port using this function:
uint8_t open_serial_port(uart_device* dev)
{
dev->fd = open(dev->path, O_RDWR | O_NOCTTY);
if (dev->fd < 0)
{
syslog(LOG_CRIT, "Serial Port {%s}-{%s} couldn't opened", dev->name, dev->path);
return EXIT_FAILURE;
}
syslog(LOG_INFO, "Serial Port {%s}-{%s} opened with fd {%d}", dev->name, dev->path, dev->fd);
struct termios tty;
if (tcgetattr(dev->fd, &tty) < 0)
{
syslog(LOG_CRIT, "Serial Connection attributes get for fd {%d} failed with errno cause {%s}", dev->fd, strerror(errno));
return EXIT_FAILURE;
}
cfmakeraw(&tty);
cfsetospeed(&tty, (speed_t) dev->speed);
cfsetispeed(&tty, (speed_t) dev->speed);
tty.c_cc[VMIN] = 255; //! This is used to block to get at least VMIN characters
tty.c_cc[VTIME] = 10; //! used to block for tens of seconds timeout 10 -> 1 seconds timeout
tty.c_cflag |= CLOCAL;
tty.c_cflag &= ~CSIZE; //! Mask the character size bits
tty.c_cflag |= get_start_stop_opt(dev->data, dev->stop); //! Set data, stop bits
tty.c_cflag |= get_parity_opt(dev->parity); //! set parity configuration
tty.c_cflag |= get_hw_flow_control(dev->flow_control);
if (tcsetattr(dev->fd, TCSANOW, &tty))
{
syslog(LOG_CRIT, "Serial Connection attributes set for fd {%d} failed with errno cause {%s}", dev->fd, strerror(errno));
return EXIT_FAILURE;
}
syslog(LOG_INFO, "Serial Connection {%s}-{%s} established. speed: %d, parity: %s, data: %d, stop: %d, flw_ctrl: %d", dev->name, dev->path, dev->speed,
dev->parity, dev->data, dev->stop, dev->flow_control);
return EXIT_SUCCESS;
}
I am reading serial port in blocking mode:
readSize = read(dev->fd, &buf, UART_MAX_PAYLOAD);
if (readSize < 0)
{
syslog(LOG_CRIT, "UART Read failed while reading {%s}, error {%s}", dev->path, strerror(errno));
usleep(1000 * 1000);
continue;
}
syslog(LOG_INFO, "Uart read completed. readSize: %d", readSize);
Actually VMIN and VTIME parameters of termios is suitable for my situation but VMIN and VTIME is defined as 8 bit. So, i can state maximum of 255 characters to read.
So, when device sends 2048 bytes of data, i read this as :
Uart read completed. readSize: 496
Uart read completed. readSize: 496
Uart read completed. readSize: 496
Uart read completed. readSize: 496
Uart read completed. readSize: 64
Somehow, i can not read whole data at same time.
What is the problem about reading large data in blocking mode? How can i read large serial data in one time?
Best regards.