UDP client and echo server using LWIP and ChibiOS 2.6.x (incomplete example for a blog post)

LwipEchoClient.cpp

// ... includes, lwip thread setup, ip/mac address, timer, statistics_recorder

struct udp_pcb * pcb_ = udp_new();

static void udp_receive(void *arg, struct udp_pcb *pcb, struct pbuf *p, struct ip_addr *addr, uint16_t port) {
  if (p != NULL) {
      // record timestamp complete and send to logging server
      stats_recorder.setValue4(timer.nanoTime());
      stats_recorder.sendto(&serverAddr, serverPort);
      stats_recorder.resetValues();
      
      // free buffer
      pbuf_free(p);
  }  
}

int main(void) { 

  // setup UDP port
  struct udp_pcb * pcb = udp_new();
  udp_bind(pcb, IP_ADDR_ANY, ECHO_PORT);
  udp_recv(pcb, udp_receive, &pcb);
  
  // send a message every 10ms
  uint32_t sequence = 0;
  systime_t time = chTimeNow(); // T0
  while (TRUE) {
    
    stats_recorder.setValue0(sequence++); // sequence number
    stats_recorder.setValue1(timer.nanoTime()); // start of loop
    pbuf * p = pbuf_alloc(PBUF_TRANSPORT, 200, PBUF_RAM);
    stats_recorder.setValue2(timer.nanoTime()); // start of packet send
      
    // send message to echo server
    if (p != NULL) {
       udp_sendto(pcb_, p, &echoAddr, ECHO_PORT);
       pbuf_free(p);
    }
        
    stats_recorder.setValue3(timer.nanoTime()); // end of packet send
        
    // Sleep until the next deadline. There is an unsigned cast because
    // there is an issue with the built-in ChibiOS 2.x implementation that
    // causes an underflow if a deadline were ever to be missed.
    time += MS2ST(2);
    int32_t ticks = int32_t(time - chTimeNow());
    if(ticks > 0){
      chThdSleep(ticks);
    } 
        
  }
}

LwipEchoServer.cpp

// ... includes, lwip thread setup, ip/mac address

static void udp_echo_receive(void *arg, struct udp_pcb *pcb, struct pbuf *p, struct ip_addr *addr, uint16_t port) {
  if (p != NULL) {
    udp_sendto(pcb, p, addr, port);
    pbuf_free(p);
  }
}

int main(void) { 

  // setup UDP port
  struct udp_pcb * pcb = udp_new();
  udp_bind(pcb, IP_ADDR_ANY, ECHO_PORT);
  udp_recv(pcb, udp_receive, &pcb);
  
  // sleep forever
  // ...
  
}