SerialStream eats up feed characters 0x0A, 0x0D, and 0x0F when reading

[JacekRuzyczka]

When communicating with a serial-over-USB device (a GNS FM9 receiver for traffic messages) using a SerialStream object, I found out that not all characters coming from the device are in fact being read. This is what I always get served:

3F 00 56 08 37 3F

When using the same device with the RDS Surveyor app (which is written in Java and uses a com.fazecast.jSerialComm.SerialPort), the response looks like this:

3F 00 00 56 08 0A 37 0C 0D 3F

After some research I stumbled over this posting: Wrong newline character over serial port (CR instead of LF). The poster does not use libserial, but his issue is exactly the same as mine.

This is the system-side config of the port in question:

pi@autoradio:~ $ stty -a speed 38400 baud; rows 40; columns 80; line = 0; intr = ^C; quit = ^\; erase = ^?; kill = ^U; eof = ^D; eol = <undef>; eol2 = <undef>; swtch = <undef>; start = ^Q; stop = ^S; susp = ^Z; rprnt = ^R; werase = ^W; lnext = ^V; discard = ^O; min = 1; time = 0; -parenb -parodd -cmspar cs8 -hupcl -cstopb cread -clocal -crtscts -ignbrk -brkint -ignpar -parmrk -inpck -istrip -inlcr -igncr icrnl ixon ixoff -iuclc -ixany -imaxbel iutf8 opost -olcuc -ocrnl onlcr -onocr -onlret -ofill -ofdel nl0 cr0 tab0 bs0 vt0 ff0 isig icanon iexten echo echoe echok -echonl -noflsh -xcase -tostop -echoprt echoctl echoke -flusho -extproc

The system is a Raspbery Pi 3B with the latest production version of Raspbian running.

Now, my question is: How can I make my SerialStream read all characters without any transformations, just as they come from the port? I don't really wanna use stty because its settings might get overwritten when removing and reattaching the device. Thank you.

NOTE: If necessary, I can post the code in question, but it's quite long.

[crayzeewulf]

@JacekRuzyczka Some sample code will surely help but I am guessing that you may be attempting to read data using >> operator. This operator is mostly used for formatted input and skips whitespaces by default. You can use std::noskipws to help with that. For binary data, it might be better to use unformatted input methods as described under the "Unformatted Input" section here. Alternatively, you may consider using the SerialPort class instead of SerialStream as it will provide you with raw data without any translation or skipping.

[JacekRuzyczka]

@crayzeewulf I'm already using the operator, just like this:

SerialStream tmc_receiver_handler ("/dev/ttyUSB0", ios::in | ios::out);
char c = 0x00;

tmc_receiver_handler.SetBaudRate      (SerialStreamBuf::BAUD_38400);
tmc_receiver_handler.SetCharSize      (SerialStreamBuf::CHAR_SIZE_8);
tmc_receiver_handler.SetFlowControl   (SerialStreamBuf::FLOW_CONTROL_NONE);
tmc_receiver_handler.SetParity        (SerialStreamBuf::PARITY_NONE);
tmc_receiver_handler.SetNumOfStopBits (SerialPort::STOP_BITS_1);

tmc_receiver_handler >> c;

[crayzeewulf]

@JacekRuzyczka The use of >> operator is likely the cause of the problem. Please try using one of the following and let us know if it works.

1. Change the last line to:

tmc_receiver_handler >> std::noskipws >> c;

2. Or, try replacing it with an unformatted input function such as:

c = tmc_receiver_handler.get() ;

[JacekRuzyczka]

Your proposal worked immediately. Thank you!

skipws is a feature of the C++ std::iostream, right?

[crayzeewulf]

Great to hear that! Thanks for letting us know.

And, yes, skipws/noskipws are part of the C++ standard input/output library.