UART read blocks after reading 33 bytes - c

Question

I have made a C-program flash image to micro controller through uart.In this code,i am following a protocol,all things are going well.But when i load image into micro controller through uart,write is working fine but read blocked after reading 33 bytes.I am writing and reading byte by byte..declaration & definition of function to load image is written below:
Function declaration :
load_RAM_image(file_size, file_buff);
here file_size is unsigned int and its value is 40,980KB and file_buff is unsigned char pointer which points to image buffer.
Function declaration :
#define BYTE_WRITE 1
#define DELAY 10000
int load_RAM_image(unsigned int buff_size, unsigned char *buff)
{
unsigned int count, num_Wbytes, num_Rbytes, byte;
for (count = 0; count < buff_size;) /* increase count value to every time */
{
num_Wbytes = write( serial_fd, buff + count, BYTE_WRITE );
if (num_Wbytes < 0)
{
fputs("write failed!\n", stderr);
return -1;
}
tcdrain(serial_fd);
usleep(DELAY);
num_Rbytes = read( serial_fd, rbuff + count, BYTE_WRITE );
if (num_Rbytes < 0)
{
if (errno == EAGAIN)
{
printf("SERIAL EAGAIN ERROR\n");
return -EAGAIN;
}
else
{
printf("SERIAL read error %d %s\n", errno, strerror(errno));
}
}
printf("wbuf[ %d ] = %02x rbuff = %02x\n\n",
count /*+ byte*/, *(buff + count/* + byte*/), rbuff[count]);
/* Compare the received byte from BAM */
if (strncmp(buff + count, rbuff + count, BYTE_WRITE ) < 0)
{
printf("Error : RAM loading error(W != R)\n");
return -1;
}
count += BYTE_WRITE ;
printf("count = %d\n", count);
}
return 0;
}