How do I change the baud rate for a LoRa device?
I have a LoRa device that uses a default baud rate of 57600 on a USB port of a raspberry pi. I'd like to experiment with faster serial baud rates. The instructions to change the baud rate after returning from a device sleep state are as follows from the datasheet:
I have one major problem in that I don't know what a 'break' code is in serial port communications. I've tried various things, including the following (where usb_port is the file descriptor of the opened port):
ioctl(usb_port, TCSBRK, 0);
and
std::string msg;
msg="0X00";
write(usb_port, msg.c_str(), msg.size());
All with no luck. Can anyone take a look at this c++ function and tell me where I may be going wrong?
From elsewhere in the documentation, it is indicated that writing "0x55" triggers an auto-baud detection setup when returning from sleep.
Note: radiodevice file descriptor of "/dev/ttyUSBPort1" is a reference to /dev/ttyUSB0 that is set up using a udev serial rule.
const char* radiodevice = "/dev/ttyUSBPort1";
int openPort(void) {
struct termios tty;
memset(&tty, 0, sizeof tty);
if ((usb_port = open(radiodevice, O_RDWR | O_NOCTTY | O_SYNC))>=0) {// | O_NOCTTY | O_SYNC
std::cout << "DEVICE OPENED: " << radiodevice << " handle number: " << usb_port << std::endl;
} else {
fprintf(stderr, "unable to open serial radiodevice");
return -1;
}
if(tcgetattr(usb_port, &tty) != 0) {
printf("Error %i \n", errno);
}
cfsetispeed(&tty, B57600);
cfsetospeed(&tty, B57600);
tty.c_cflag &= ~PARENB; // Make 8n1
tty.c_cflag &= ~CSTOPB;
tty.c_cflag &= ~CSIZE;
tty.c_cflag |= CS8;
tty.c_cflag &= ~CRTSCTS; // no flow control
tty.c_cc[VMIN] = 0; // read doesn't block
tty.c_cc[VTIME] = 5; // 0.5 seconds read timeout
tty.c_iflag &= ~ISTRIP;
tty.c_iflag &= ~INLCR;
tty.c_iflag &= ~IGNCR;
tty.c_iflag &= ~ICRNL;
tty.c_oflag &= OPOST;
tty.c_lflag &= ICANON;
tcflush(usb_port,TCIOFLUSH);
usleep(10000);
if (tcsetattr(usb_port, TCSANOW, &tty) != 0) {
printf("Error %i\n", errno);
}
//FLASH UNIT LED LIGHTS TO CONFIRM INITIAL CONNECTION
std::string msg="sys set pindig GPIO11 1\r\n";
write(usb_port, msg.c_str(), msg.size());
usleep(1000000);
msg="sys set pindig GPIO11 0\r\n";
write(usb_port, msg.c_str(), msg.size());
usleep(10000);
//WRITE SLEEP COMMAND TO DEVICE FOR 0.5 SECONDS
std::cout << "WRITING SLEEP COMMAND" << std::endl;
msg="sys sleep 5000\r\n";//
write(usb_port, msg.c_str(), msg.size());
usleep(100000);
//ATTEMPT TO SEND BREAK COMMAND
ioctl(usb_port, TCSBRK, 0);
usleep(500000);
//RESET SERIAL BAUD RATE
cfsetispeed(&tty, B115200);
cfsetospeed(&tty, B115200);
//SET DEVICE TO AUTO-BAUD RATE DETECTION
std::cout << "SENDING 0x55" << std::endl;
msg="0x55";
write(usb_port, msg.c_str(), msg.size());
usleep(2000000);
//FLASH UNIT LED LIGHTS TO CONFIRM FINAL CONNECTION AT NEW BAUD RATE
std::cout << "BLINKING LIGHTS" << std::endl;
msg="sys set pindig GPIO11 1\r\n";
write(usb_port, msg.c_str(), msg.size());
usleep(1000000);
msg="sys set pindig GPIO11 0\r\n";
write(usb_port, msg.c_str(), msg.size());
return usb_port;
}
Solution
For those that may be searching for this solution down the road, here's the way I accomplished the task of setting the LoRa device into auto baud mode and opening the port at the new baud rate:
int openPort(void) {
struct termios tty;
memset(&tty, 0, sizeof tty);
//OPEN PORT WITH DEFAULT BAUD RATE 57600
if ((usb_port = open(radiodevice, O_RDWR | O_NOCTTY | O_SYNC))>=0) {// | O_NOCTTY | O_SYNC
std::cout << "DEVICE OPENED: " << radiodevice << " handle number: " << usb_port << std::endl;
} else {
fprintf(stderr, "unable to open serial radiodevice");
return -1;
}
if(tcgetattr(usb_port, &tty) != 0) {
printf("Error %i \n", errno);
}
cfsetispeed(&tty, B57600);
cfsetospeed(&tty, B57600);
tty.c_cflag &= ~PARENB; // Make 8n1
tty.c_cflag &= ~CSTOPB;
tty.c_cflag &= ~CSIZE;
tty.c_cflag |= CS8;
tty.c_cflag &= ~CRTSCTS; // no flow control
tty.c_cc[VMIN] = 0; // read doesn't block
tty.c_cc[VTIME] = 5; // 0.5 seconds read timeout
tty.c_iflag &= ~ISTRIP;
tty.c_iflag &= ~INLCR;
tty.c_iflag &= ~IGNCR;
tty.c_iflag &= ~ICRNL;
tty.c_oflag &= OPOST;
tty.c_lflag &= ICANON;
tcflush(usb_port,TCIOFLUSH);
//usleep(10000);
if (tcsetattr(usb_port, TCSANOW, &tty) != 0) {
printf("Error %i\n", errno);
}
//FLASH UNIT LED LIGHTS TO CONFIRM INITIAL CONNECTION
std::string msg="sys set pindig GPIO11 1\r\n";
write(usb_port, msg.c_str(), msg.size());
usleep(1000000);
msg="sys set pindig GPIO11 0\r\n";
write(usb_port, msg.c_str(), msg.size());
usleep(10000);
//WRITE SLEEP COMMAND TO DEVICE FOR 0.5 SECONDS
std::cout << "WRITING SLEEP COMMAND" << std::endl;
msg="sys sleep 5000\r\n";
write(usb_port, msg.c_str(), msg.size());
usleep(100000);
close(usb_port);
//OPEN PORT AT NEW BAUD RATE
if ((usb_port = open(radiodevice, O_RDWR | O_NOCTTY | O_SYNC))>=0) {// | O_NOCTTY | O_SYNC
std::cout << "DEVICE OPENED: " << radiodevice << " handle number: " << usb_port << std::endl;
} else {
fprintf(stderr, "unable to open serial radiodevice");
return -1;
}
if(tcgetattr(usb_port, &tty) != 0) {
printf("Error %i \n", errno);
}
//RESET SERIAL BAUD RATE
cfsetispeed(&tty, B230400);<---SET NEW BAUD RATE VALUE
cfsetospeed(&tty, B230400);<---SET NEW BAUD RATE VALUE
tty.c_cflag &= ~PARENB; // Make 8n1
tty.c_cflag &= ~CSTOPB;
tty.c_cflag &= ~CSIZE;
tty.c_cflag |= CS8;
tty.c_cflag &= ~CRTSCTS; // no flow control
tty.c_cc[VMIN] = 0; // read doesn't block
tty.c_cc[VTIME] = 5; // 0.5 seconds read timeout
tty.c_iflag &= ~ISTRIP;
tty.c_iflag &= ~INLCR;
tty.c_iflag &= ~IGNCR;
tty.c_iflag &= ~ICRNL;
tty.c_oflag &= OPOST;
tty.c_lflag &= ICANON;
tcflush(usb_port,TCIOFLUSH);
usleep(10000);
if (tcsetattr(usb_port, TCSANOW, &tty) != 0) {
printf("Error %i\n", errno);
}
//SEND BREAK COMMAND
std::cout << "SENDING BREAK COMMAND" << std::endl;
tcsendbreak(usb_port, 0);
usleep(10000);
//SET DEVICE TO AUTO-BAUD RATE DETECTION
msg = "U";//CORRESPONDS TO DOCUMENTED CHARACTER 0x55
write(usb_port, msg.c_str(), msg.size());
//FLASH UNIT LED LIGHTS TO CONFIRM FINAL CONNECTION AT NEW BAUD RATE
std::cout << "BLINKING LIGHTS" << std::endl;
msg="sys set pindig GPIO11 1\r\n";
write(usb_port, msg.c_str(), msg.size());
usleep(1000000);
msg="sys set pindig GPIO11 0\r\n";
write(usb_port, msg.c_str(), msg.size());
return usb_port;
}
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