Why does Ubuntu throw an I/O error randomly? - c++

Question

I have got a PC/104 (its OS is Ubuntu 16.04 with kernel 4.19.89 xenomai3) that is connected to two motors via two CAN adapters. Few days back, I wrote some simple code to open my PC/104's CAN ports using the libpcanfd library.
My project folder observes the following hierarchy:
io_error_debug
build
include (empty)
src
CMakeLists.txt
main.cpp
CMakeLists.txt
CMakeLists.txt at /root:
cmake_minimum_required(VERSION 2.6)
project(io_error_debug)
include_directories(${PROJECT_SOURCE_DIR}/include) # add before adding subdirectory
add_subdirectory (src)
add_executable(io_error_debug src/main.cpp)
target_link_libraries(io_error_debug /usr/lib/libpcanfd.so # pcan
"-Wl,--no-as-needed -Wl,#/usr/xenomai/lib/cobalt.wrappers -Wl,#/usr/xenomai /lib/modechk.wrappers /usr/xenomai/lib/xenomai/bootstrap-pic.o -L/usr/xenomai/lib -lcobalt -lmodechk -lpthread -lrt"
)
CMakeLists.txt under /src:
aux_source_directory(. SRC_LIST)
main.cpp:
#include <sys/time.h>
#include <lcm/lcm_coretypes.h>
#include <math.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/mman.h>
#include <inttypes.h>
#include <unistd.h>
#include <fcntl.h>
#include <signal.h>
#include <pthread.h>
#include <errno.h>
#include <sys/syscall.h>
#include <pcanfd.h>
#include <libpcanfd.h>
#include <cmath>
#include <iostream>
int main(int argc, char *argv[]){
int fd;
fd = pcanfd_open("/dev/pcan0", OFD_BITRATE | PCANFD_INIT_STD_MSG_ONLY | OFD_NONBLOCKING, 1000000);
if (fd < 0)
{
printf("Open operation failed with err %d on port no. %s\n",fd, "/dev/pcan0");
exit(1);
}else{
printf("Open succeeded with return value %d on port no. %s\n",fd, "/dev/pcan0");
}
}
The code compiles and executes well when the motors are switched on. However, when I switch off the motors and switch them on again, I get the following error after executing my code:
Open operation failed with err -5 on port no. /dev/pcan0
Furthermore, dmesg shows these suspicious error lines when I run my code:
[16900.914132] pcan: set_normal_mode(CAN1) failed (err -5)
[16900.914162] pcan: can't open device hardware itself (err -5)!
The documentation states that -5 is an errno error. Therefore, I looked for the value -5 in this errno errors' list and I found out that it isI/O error. Interestingly, when I switch off the PC/104 and execute my code, the program runs well. Nevertheless, when I repeat the aforementioned operation (i.e., switching off and on the motors) I will encounter the same error. I do not understand what is happening.