EthernetClient - flush() does uip_poll_conn. my strong buffering removed

It turned out, it is better not to wait for the buffer to fill, but to
send the packet right after ACK for the previous packet.

flush() is implemented to send a packet immediately if there is no
outstanding packet.

Author: JAndrassy

README.md

@@ -5,7 +5,8 @@ The modernization includes:
 * Ethernet 2.0 library functions
 * support of many Arduino architectures by using the SPI library
 * SPI transactions to share the SPI bus with devices with different communication settings
-* heavy buffering of sent TCP data in ENC with flush() function to send the last buffer
+* SPI communication at 20 MHz if the MCU supports it, else on the maximum supported by the MCU
+* client.flush() to send the packet immediately
 
 [The documentation of Arduino Ethernet library](https://www.arduino.cc/en/Reference/Ethernet) applies for class and functions descriptions.
 

src/EthernetClient.cpp

@@ -115,6 +115,7 @@ UIPClient::stop()
         }
       else
         {
+          flush();
           data->state |= UIP_CLIENT_CLOSE;
         }
 #ifdef UIPETHERNET_DEBUG_CLIENT
@@ -205,6 +206,8 @@ UIPClient::write(const uint8_t *buf, size_t size)
       u->out_pos+=written;
       if (remain > 0)
         {
+          if (p == 0) // block 0 just filled, start sending immediately
+            flush();
           if (p == UIP_SOCKET_NUMPACKETS-1)
             {
 #if UIP_WRITE_TIMEOUT > 0
@@ -240,8 +243,21 @@ UIPClient::availableForWrite()
 void
 UIPClient::flush()
 {
+  UIPEthernetClass::tick();
+
   if (data && data->packets_out[0] != NOBLOCK)
-    data->state |= UIP_CLIENT_FLUSH;
+    {
+      struct uip_conn* conn = &uip_conns[data->conn_index];
+      if (!uip_outstanding(conn))
+        {
+          uip_poll_conn(conn);
+          if (uip_len > 0)
+            {
+              uip_arp_out();
+              UIPEthernetClass::network_send();
+            }
+        }
+    }
 }
 
 int
@@ -439,8 +455,6 @@ uipclient_appcall(void)
           Serial.println(F("UIPClient uip_acked"));
 #endif
           UIPClient::_eatBlock(u->packets_out);
-          if (u->packets_out[0] == NOBLOCK)
-            u->state &= ~UIP_CLIENT_FLUSH;
           goto send;
         }
       if (uip_poll() || uip_rexmit())
@@ -453,14 +467,12 @@ uipclient_appcall(void)
             {
               if (u->packets_out[1] == NOBLOCK)
                 {
-                 if ((u->state & UIP_CLIENT_FLUSH) || (u->state & UIP_CLIENT_CLOSE)) {
                   send_len = u->out_pos;
                   if (send_len > 0)
                     {
                       Enc28J60Network::resizeBlock(u->packets_out[0],0,send_len);
                     }
                  }
-                }
               else
                 send_len = Enc28J60Network::blockSize(u->packets_out[0]);
               if (send_len > 0)

src/EthernetClient.h

@@ -34,7 +34,6 @@ extern "C" {
 #define UIP_CLIENT_REMOTECLOSED 0x04
 #define UIP_CLIENT_RESTART 0x08
 #define UIP_CLIENT_ACCEPTED 0x10
-#define UIP_CLIENT_FLUSH 0x20
 
 typedef struct {
   uint8_t conn_index;