/* sends next data block during TFTP READ operation  */
void tftp_send_next_block(struct udp_pcb *upcb, tftp_connection_args *args, const ip_addr_t *to_ip, u16_t to_port)
/* sends next data block during TFTP READ operation  */
void tftp_send_next_block(struct udp_pcb *upcb, tftp_connection_args *args, const ip_addr_t *to_ip, u16_t to_port)
{
   f_read(&file_SD, (uint8_t*)args->data, TFTP_DATA_LEN_MAX, (UINT*)(&args->data_len));
  tftp_send_data_packet(upcb, to_ip, to_port, args->block, args->data, args->data_len);
}