C program to read data from USB device connected to the system - c

Question

I am trying to fetch data from the USB device (say pendrive) connected to the USB port of a system. Here, I am able to open the device file and read some random raw data. But I want to fetch data like minicom/teraterm.
Please let me know what methods and libraries I can use to do it successfully and how can it be done.
#include <stdio.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <fcntl.h>
#include <errno.h>
#include <termios.h>
#include <signal.h>
#include <sys/time.h>
int main()
{
short portfd=-1;
int n,f,len;
char buf[256],*s;
alarm(2);
#if defined(O_NDELAY) && defined(F_SETFL)
portfd = open("/dev/ttyUSB0", O_RDWR|O_NDELAY);
if (portfd >= 0){
/* Cancel the O_NDELAY flag. */
printf("port openend\n");
n = fcntl(portfd, F_GETFL, 0);
(void) fcntl(portfd, F_SETFL, n & ~O_NDELAY);
}
#else
portfd = open("/dev/ttyUSB0", O_RDWR);
#endif
if (portfd >= 0)
{
if (len == 0) len = strlen(s);
for(f = 0; f < len && f <100; f++)
buf[f] = *s++ | 0x80;
write(portfd, buf, f);
printf("Do write\n");
while(portfd>=0){
printf("%s\n",buf);
}
}
alarm(0);
signal(SIGALRM, SIG_IGN);
if (portfd < 0) {
printf("cannot open %s. Sorry.\n", "/dev/ttyUSB0");
}
}
Log of the output:
���������鉀�������������������鍀���������������������������������������������������������������2
����������鉀�������������������鍀���������������������������������������������������������������2

Answer 1

you will need to set the correct port configuration...
struct termios oldtio,newtio;
// open port...
// save existing attributes
tcgetattr(fd,&oldtio);
// set attributes - these flags may change for your device
#define BAUDRATE B9600
memset(&newtio, 0x00, sizeof(newtio));
newtio.c_cflag = BAUDRATE | CRTSCTS | CS8 | CLOCAL | CREAD;
newtio.c_iflag = IGNPAR | ICRNL;
newtio.c_oflag = 0;
tcflush(fd, TCIFLUSH);
tcsetattr(fd,TCSANOW,&newtio);
//reset attributes
tcsetattr(fd,TCSANOW,&oldtio);
I have a rough working example here... http://file-hub.com/cmd:thread/142300