Unable to read serial data on a raspberry pi 3B
pranavlal opened this issue · 4 comments
Hi all,
I am trying to read the values of 2 ultrasound sensors that have USB serial interfaces. Both are connected to my raspberry pi running raspbian buster.
The sensors and ports are working because I can get readings in python. I am trying to get readings in C++.
I am able to open the ports but do not seem to get any data so none of the loops execute.
while(frontSensorStream.rdbuf()->in_avail() > 0 && backSensorStream.rdbuf()->in_avail() > 0)
I am pasting my entire code below. What is the error I am making?
#include
#include
#include
#include
#include
using namespace LibSerial ;
using namespace std;
constexpr const char* const SERIAL_PORT_FRONT = "/dev/ttyUSB0" ;
constexpr const char* const SERIAL_PORT_BACK = "/dev/ttyUSB1" ;
void signal_callback_handler(int signum)
{
exit(signum);
}
int main()
{
SerialStream frontSensorStream;
SerialStream backSensorStream;
signal(SIGINT, signal_callback_handler);
std::cout << "program started" << endl;
try
{
frontSensorStream.Open(SERIAL_PORT_FRONT);
}
catch (const OpenFailed&)
{
std::cerr << "The serial port did not open correctly." << std::endl ;
return EXIT_FAILURE ;
}
try
{
backSensorStream.Open(SERIAL_PORT_BACK);
}
catch (const OpenFailed&)
{
std::cerr << "The serial port did not open correctly." << std::endl;
return EXIT_FAILURE ;
}
frontSensorStream.SetBaudRate(BaudRate::BAUD_57600);
backSensorStream.SetBaudRate(BaudRate::BAUD_57600);
frontSensorStream.SetCharacterSize(CharacterSize::CHAR_SIZE_8);
backSensorStream.SetCharacterSize(CharacterSize::CHAR_SIZE_8);
frontSensorStream.SetStopBits(StopBits::STOP_BITS_1);
backSensorStream.SetStopBits(StopBits::STOP_BITS_1);
frontSensorStream.SetParity(Parity::PARITY_NONE) ;
backSensorStream.SetParity(Parity::PARITY_NONE) ;
frontSensorStream.SetFlowControl(FlowControl::FLOW_CONTROL_NONE) ;
backSensorStream.SetFlowControl(FlowControl::FLOW_CONTROL_NONE) ;
usleep(2000);
std::cout << "ports opened, about to start capture" << endl;
while(frontSensorStream.rdbuf()->in_avail() > 0 && backSensorStream.rdbuf()->in_avail() > 0)
{
while(frontSensorStream.IsDataAvailable() && backSensorStream.IsDataAvailable())
{
char frontSensorData;
char backSensorData;
frontSensorStream.get(frontSensorData);
backSensorStream.get(backSensorData);
std::cout << "front sensor=" << frontSensorData << endl;
std::cout << "back sensor=" << backSensorData << endl;
usleep(1000);
}
}
frontSensorStream.Close();
backSensorStream.Close();
std::cout << "program done" << endl;
return EXIT_SUCCESS ;
}
I have installed libserial from source and did not get any error messages during the make process.
Hi @pranavlal ,
I think your issue is stemming from possibly a small logic error as well as physical timing. With minor modification I am able to run the code you posted above and everything executes properly.
Please review the program I have attached here (based on your code with a few small modifications) and let us know if your error persists. Note the && change to || in your while loop and the elimination of your outer while() loop as it was somewhat a repetition of your inner loop logic.
(@pranavlal , I've pushed up a branch with the example mentioned just above included in the examples directory that you can checkout, compile, and run here.)
@mcsauder,
Many many thanks. The program works!
I now need to add some more code to compare values etc. Time to get reacquainted with C.
Great to hear!