Hello,
1. I am trying to implement Modbus TCP Client, on a custom LPC1778 board,
with NO_SYS=1, raw_api, and 'lpc177x_40xx_emac.c' EMAC driver
(contained in lpclwip implementation, that is part of LPCOPEN libraries)
2. The example client program sends the data in connected callback.
3. Obviously, I can't implement it this way as the data needs to be sent
and received multiple times during the life of the connection.
4. Hence, I plan to send data from outside the lwip callbacks.
5. Following is the 'Connected' callback implementation in the example
// *******************************************************************
/* structure to be passed as argument to the tcp callbacks */
struct echoclient
{
enum echoclient_states state; /* connection status */
struct tcp_pcb *pcb; /* pointer on the current tcp_pcb */
struct pbuf *p_tx; /* pointer on pbuf to be transmitted */
};
static err_t tcp_echoclient_connected(void *arg, struct tcp_pcb *tpcb,
err_t err)
{
struct echoclient *es = NULL;
if (err == ERR_OK)
{
/* allocate structure es to maintain tcp connection informations */
es = (struct echoclient *)mem_malloc(sizeof(struct echoclient));
if (es != NULL)
{
es->state = ES_CONNECTED;
es->pcb = tpcb;
sprintf((char*)data, "sending tcp client message %d",
(int)message_count++);
/* allocate pbuf */
es->p_tx = pbuf_alloc(PBUF_TRANSPORT, strlen((char*)data) ,
PBUF_POOL);
if (es->p_tx)
{
/* copy data to pbuf */
pbuf_take(es->p_tx, (char*)data, strlen((char*)data));
/* pass newly allocated es structure as argument to tpcb */
tcp_arg(tpcb, es);
/* initialize LwIP tcp_recv callback function */
tcp_recv(tpcb, tcp_echoclient_recv);
/* initialize LwIP tcp_sent callback function */
tcp_sent(tpcb, tcp_echoclient_sent);
/* initialize LwIP tcp_poll callback function */
tcp_poll(tpcb, tcp_echoclient_poll, 1);
/* send data */
tcp_echoclient_send(tpcb,es);
return ERR_OK;
}
}
else
{
/* close connection */
tcp_echoclient_connection_close(tpcb, es);
/* return memory allocation error */
return ERR_MEM;
}
}
else
{
/* close connection */
tcp_echoclient_connection_close(tpcb, es);
}
return err;
}
// *******************************************************************
6. My doubts are as follows,
6.1 Is 'es' the pointer to echoclient structure (initialized thro' malloc)
and passed to lwip
as 'arg' in it's callbacks AND the member 'tpcb' (struct tcp_pcb *tpcb)
passed by lwip, ARE INVARIANT during the life of the connection
6.2 If that is so (which should be), I can save this in a global variable
in the connected callback and use it from other segments of the program.
6.3 This should serve my purpose,
Thank you very much.
- Vijay Vaidya
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