netconn_evt enum

Used to inform the callback function about changes Event explanation: In the netconn implementation, there are three ways to block a client: - accept mbox (sys_arch_mbox_fetch(&conn->acceptmbox, &accept_ptr, 0); in netconn_accept()) - receive mbox (sys_arch_mbox_fetch(&conn->recvmbox, &buf, 0); in netconn_recv_data()) - send queue is full (sys_arch_sem_wait(LWIP_API_MSG_SEM(msg), 0); in lwip_netconn_do_write()) The events have to be seen as events signaling the state of these mboxes/semaphores. For non-blocking connections, you need to know in advance whether a call to a netconn function call would block or not, and these events tell you about that. RCVPLUS events say: Safe to perform a potentially blocking call call once more. They are counted in sockets - three RCVPLUS events for accept mbox means you are safe to call netconn_accept 3 times without being blocked. Same thing for receive mbox. RCVMINUS events say: Your call to to a possibly blocking function is "acknowledged". Socket implementation decrements the counter. For TX, there is no need to count, its merely a flag. SENDPLUS means you may send something. SENDPLUS occurs when enough data was delivered to peer so netconn_send() can be called again. A SENDMINUS event occurs when the next call to a netconn_send() would be blocking.