File content as of revision 2:8f3478b5d434:

#include "mbed.h"
#include "USBHostSerial.h"

DigitalOut led(LED1);
Serial pc(USBTX, USBRX);

void serial_task(void const*) {
    USBHostSerial serial;
    
    while(1) {
    
        // try to connect a serial device
        while(!serial.connect())
            Thread::wait(500);
        
        // in a loop, print all characters received
        // if the device is disconnected, we try to connect it again
        while (1) {
        
            // if device disconnected, try to connect it again
            if (!serial.connected())
                break;

            // print characters received
            while (serial.available()) {
                printf("%c", serial.getc());
            }
            
            Thread::wait(50);
        }
    }
}

int main() {
    Thread serialTask(serial_task, NULL, osPriorityNormal, 256 * 4);
    while(1) {
        led=!led;
        Thread::wait(500);
    }
}