I am working on project which requires to send command in hex with device setting as follows : Baud rate : 9600, Parity : None, Stop bits : 2 , data bits : 8 (9600, 8N2).
I have verified by sending data to device with minicom. I am able to see data on CRO. But when I am sending data via C code and unable to see data on CRO and getting program output as FFFFF always for read function.
Source code for serial read and write :
int32_t Read()
{
printf("Entering Read function \n");
int fd;
fd = open("/dev/ttyS1", O_RDWR | O_NOCTTY | O_NDELAY);
int j=0;
if (fd == -1)
{
perror("open_port: Unable to open /dev/ttyS1\n");
exit(1);
}
else
{
printf("Port /dev/ttyS1 opened successfully\n");
}
//---------- Setting the Attributes of the serial port using termios structure ---------
struct termios SerialPortSettings; // Create the structure
tcgetattr(fd, &SerialPortSettings); // Get the current attributes of the Serial port
cfsetispeed(&SerialPortSettings,B9600); // Set Read Speed as 9600
cfsetospeed(&SerialPortSettings,B9600); // Set Write Speed as 9600
SerialPortSettings.c_cflag &= ~PARENB; // Disables the Parity Enable bit(PARENB),So No Parity
SerialPortSettings.c_cflag &= ~PARODD; // added
SerialPortSettings.c_cflag |= CS8; // Set the data bits = 8
SerialPortSettings.c_cflag &= CSTOPB; // CSTOPB = 2 Stop bits
SerialPortSettings.c_cflag &= ~CSIZE; // Clears the mask for setting the data size
SerialPortSettings.c_cflag &= ~CRTSCTS; // No Hardware flow Control
SerialPortSettings.c_cflag |= (CREAD | CLOCAL); // Enable receiver,Ignore Modem Control lines
SerialPortSettings.c_lflag =0; /* RAW input */ // added
SerialPortSettings.c_iflag &= ~(IXON | IXOFF | IXANY); // Disable XON/XOFF flow control both i/p and o/p
SerialPortSettings.c_iflag &= ~(ICANON | ECHO | ECHOE | ISIG); // Non Cannonical mode
SerialPortSettings.c_cc[VMIN] = 0; // added for testing // added 1 sec
SerialPortSettings.c_cc[VTIME] = 5; // added for testing // added
SerialPortSettings.c_iflag = 0; /* SW flow control off, no parity checks etc */ // added
SerialPortSettings.c_oflag &= ~OPOST;// No Output Processing
if((tcsetattr(fd,TCSANOW,&SerialPortSettings)) != 0) // Set the attributes to the termios structure
printf("\n ERROR ! in Setting attributes");
else
printf("\n BaudRate = 9600 \n StopBits = 2 \n Parity = None\n");
//------------------------------- Write data to serial port -----------------------------
unsigned char write_buffer[] = {0x28,0x11,0xDF,0xBC}; // Buffer containing characters to write into port
int bytes_written = 0; // Value for storing the number of bytes written to the port
for(j=0;j<4;j++)
{
bytes_written = write(fd,write_buffer[j],sizeof(write_buffer));// use write() to send data to port
// "fd" - file descriptor pointing to the opened serial port
// "write_buffer" - address of the buffer containing data
// "sizeof(write_buffer)" - No of bytes to write
//
printf("Byte written : %x\n",write_buffer[j]);
printf("\n %d Bytes written to ttyS1", bytes_written);
printf("\n +----------------------------------+\n\n");
}
sleep(2);
//------------------------------- Read data from serial port -----------------------------
tcflush(fd, TCIFLUSH); // Discards old data in the rx buffer
unsigned char read_buffer[40]; // Buffer to store the data received
int bytes_read = 0; // Number of bytes read by the read() system call
int i = 0;
bytes_read = read(fd,&read_buffer,40); // Read the data
printf("\n\n Bytes Rxed -%x", bytes_read); // Print the number of bytes read
printf("\n\n ");
for(i=0;i<bytes_read;i++) //printing only the received characters
printf("%x",(int)(*(unsigned char*)(&read_buffer[i])));
printf("\n +----------------------------------+\n\n\n");
close(fd); // Close the serial port
printf("Exiting Read function \n");
}
Output :
Entering Read function
Port /dev/ttyS1 opened successfully
BaudRate = 9600
StopBits = 2
Parity = None
Byte written : 28
-1 Bytes written to ttyS1
+----------------------------------+
Byte written : 11
-1 Bytes written to ttyS1
+----------------------------------+
Byte written : df
-1 Bytes written to ttyS1
+----------------------------------+
Byte written : bc
-1 Bytes written to ttyS1
+----------------------------------+
Bytes Rxed -ffffffff
+----------------------------------+
Exiting Read function
1st of all add error checking to this call:
tcgetattr(fd, &SerialPortSettings);
like
if (0 > tcgetattr(fd, &SerialPortSettings))
{
/* log and handle error */
}
Then here
SerialPortSettings.c_cflag |= CS8;
you set the data bits.
Two lines below you clear it
SerialPortSettings.c_cflag &= ~CSIZE;
Do this the other way round.
Also this
SerialPortSettings.c_cflag &= CSTOPB;
unsets.
If you want to use 2 stop bits set it by doing
SerialPortSettings.c_cflag |= CSTOPB;
Instead of just doing
SerialPortSettings.c_oflag &= ~OPOST;
do
SerialPortSettings.c_oflag = 0;
The code calls write() wrongly. This
for(j=0;j<4;j++)
{
bytes_written = write(fd,write_buffer[j],sizeof(write_buffer));
ought to be
for(j=0;j<4;j++)
{
bytes_written = write(fd, &write_buffer[j], 1)
Or just drop the loop and do
bytes_written = write(fd, write_buffer, sizeof write_buffer);
The call to read() is wrong as well.
It should be
bytes_read = read(fd, read_buffer, ...
For some of those mistakes with write and read the compiler should have warned you about.
Please also note that read() and write() return ssize_t not int.
Last not least I doubt flushing the input buffer (tcflush(fd, TCIFLUSH);) before reading it makes sense.