lwip: Allow several configuration macros to be set externally (bis)

features/FEATURE_LWIP/lwip-interface/lwipopts.h

@@ -105,12 +105,54 @@
 
 #define LWIP_RAM_HEAP_POINTER       lwip_ram_heap
 
+// Number of pool pbufs.
+// Each requires 684 bytes of RAM.
+#ifndef PBUF_POOL_SIZE
 #define PBUF_POOL_SIZE              5
+#endif
+
+// One tcp_pcb_listen is needed for each TCPServer.
+// Each requires 72 bytes of RAM.
+#ifdef MBED_CONF_LWIP_TCP_SERVER_MAX
+#define MEMP_NUM_TCP_PCB_LISTEN     MBED_CONF_LWIP_TCP_SERVER_MAX
+#else
 #define MEMP_NUM_TCP_PCB_LISTEN     4
+#endif
+
+// One is tcp_pcb needed for each TCPSocket.
+// Each requires 196 bytes of RAM.
+#ifdef MBED_CONF_LWIP_TCP_SOCKET_MAX
+#define MEMP_NUM_TCP_PCB            MBED_CONF_LWIP_TCP_SOCKET_MAX
+#else
 #define MEMP_NUM_TCP_PCB            4
+#endif
+
+// One udp_pcb is needed for each UDPSocket.
+// Each requires 84 bytes of RAM (total rounded to multiple of 512).
+#ifdef MBED_CONF_LWIP_UDP_SOCKET_MAX
+#define MEMP_NUM_UDP_PCB            MBED_CONF_LWIP_UDP_SOCKET_MAX
+#else
 #define MEMP_NUM_UDP_PCB            4
+#endif
+
+// Number of non-pool pbufs.
+// Each requires 92 bytes of RAM.
+#ifndef MEMP_NUM_PBUF
 #define MEMP_NUM_PBUF               8
+#endif
+
+// Each netbuf requires 64 bytes of RAM.
+#ifndef MEMP_NUM_NETBUF
 #define MEMP_NUM_NETBUF             8
+#endif
+
+// One netconn is needed for each UDPSocket, TCPSocket or TCPServer.
+// Each requires 236 bytes of RAM (total rounded to multiple of 512).
+#ifdef MBED_CONF_LWIP_SOCKET_MAX
+#define MEMP_NUM_NETCONN            MBED_CONF_LWIP_SOCKET_MAX
+#else
+#define MEMP_NUM_NETCONN            4
+#endif
 
 #define TCP_QUEUE_OOSEQ             0
 #define TCP_OVERSIZE                0

features/FEATURE_LWIP/lwip-interface/mbed_lib.json

@@ -16,6 +16,22 @@
         "addr-timeout": {
             "help": "On dual stack system how long to wait preferred stack's address in seconds",
             "value": 5
+        },
+        "socket-max": {
+            "help": "Maximum number of open TCPServer, TCPSocket and UDPSocket instances allowed, including one used internally for DNS.  Each requires 236 bytes of pre-allocated RAM",
+            "value": 4
+        },
+        "tcp-server-max": {
+            "help": "Maximum number of open TCPServer instances allowed.  Each requires 72 bytes of pre-allocated RAM",
+            "value": 4
+        },
+        "tcp-socket-max": {
+            "help": "Maximum number of open TCPSocket instances allowed.  Each requires 196 bytes of pre-allocated RAM",
+            "value": 4
+        },
+        "udp-socket-max": {
+            "help": "Maximum number of open UDPSocket instances allowed, including one used internally for DNS.  Each requires 84 bytes of pre-allocated RAM",
+            "value": 4
         }
     }
 }