`static void usb_serial_jtag_isr_handler(void *arg) {
uint32_t flags = usb_serial_jtag_ll_get_intsts_mask();

if (flags & USB_SERIAL_JTAG_INTR_SOF) {       
    usb_serial_jtag_ll_clr_intsts_mask(USB_SERIAL_JTAG_INTR_SOF);        
}   

if (flags & USB_SERIAL_JTAG_INTR_SERIAL_OUT_RECV_PKT) {       
    usb_serial_jtag_ll_clr_intsts_mask(USB_SERIAL_JTAG_INTR_SERIAL_OUT_RECV_PKT);
    /*  
     The commented part has bugs.  
     Assume the PC sends data very fast, such as 500 bytes (can be simulated by pasting),
     After multiple interrupts, stdin_ringbuf will be full, that is, req_len = 0 below.  
     Since the interrupt has been cleared, the USB buffer cannot be read out, 
     interrupts will never happen again, causing the USB to fail and the link to eventually break. 
     Simply changing to  
     usb_serial_jtag_ll_read_rxfifo(rx_buf, USB_SERIAL_JTAG_BUF_SIZE)  
     can ensure normal operation. Of course, poll and other methods can also be used to fix this bug.
    */
    //size_t req_len = ringbuf_free(&stdin_ringbuf);        
    //if (req_len > USB_SERIAL_JTAG_BUF_SIZE) {         
    //    req_len = USB_SERIAL_JTAG_BUF_SIZE;         
    //}         
    //size_t len = usb_serial_jtag_ll_read_rxfifo(rx_buf, req_len);         
    size_t len = usb_serial_jtag_ll_read_rxfifo(rx_buf, USB_SERIAL_JTAG_BUF_SIZE);         
    for (size_t i = 0; i < len; ++i) {             
        if (rx_buf[i] == mp_interrupt_char) {                 
        mp_sched_keyboard_interrupt();             
        } else {                 
            ringbuf_put(&stdin_ringbuf, rx_buf[i]);             
        }         
    }          
    mp_hal_wake_main_task_from_isr();     
}  

}
`