File content as of revision 0:7528379ed84d:

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

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

void serial_task(void const*) {
    char buf[100];
    USBHostSerial serial;
    
    while(1) {
    
        // try to connect a virtual serial port
        while(!serial.connect())
            Thread::wait(500);
    
        while(1) {
        
            // if serial not connected, try to connect again
            if (!serial.connected())
                break;
                
            // if char available on the virtual serial port, print them
            if (serial.available()) {
                serial.scanf("%s", buf);
                printf("recv: %s\r\n", buf);
            }
            
        }
        
    }
}

int main() {
    Thread serialTask(serial_task, NULL, osPriorityNormal, 1024 * 4);
    while(1) {
        led=!led;
        Thread::wait(500);
    }
}