/* Number of free bytes in the Send buffer.  */
int32_t USBD_CDC_ACM_DataFree(void)
/* Number of free bytes in the Send buffer.  */
int32_t USBD_CDC_ACM_DataFree(void)
{
    return ((int32_t)usbd_cdc_acm_sendbuf_sz) - (data_to_send_wr - data_to_send_rd);
}