#include "mbed.h"
#include "USBSerial.h"

USBSerial serial;

void readISR() {
	while(serial.readable()) {
		serial._getc();
	}
}

int main(void) {
    serial.attach(readISR);
    while(1)
    {
    	for(int i=0; i<100; i++) {
    		if(serial.writeable()) {
    			serial._putc('.');
    		}
    	}
    	wait_ms(5);
    	if(serial.writeable()) {
    	    serial._putc('\n');
    	}	
    }
}

I'm using a Nucleo F401RE board to help me debug a problem with the USBSerial library and this micro. I've attached a USB connector to PA12 (D+), PA11 (D-), GND, and PA9 (+5V). The board is powered from the embedded STLINK USB and the clock is configured by default (board revision C-03) to use the MCO from ST-LINK. The library works well for simple reads and writes. However, when I stress it a little it freezes. Here is a simple program that hangs the board when approximately 300 bytes are transferred from the PC to the board in a single shot. <<code>> #include "mbed.h" #include "USBSerial.h" USBSerial serial; void readISR() { while(serial.readable()) { serial._getc(); } } int main(void) { serial.attach(readISR); while(1) { for(int i=0; i<100; i++) { if(serial.writeable()) { serial._putc('.'); } } wait_ms(5); if(serial.writeable()) { serial._putc('\n'); } } } <</code>>