esp-lwip

LwIP library for ESP8266. This work is based on the LwIP code drop done by Espressif in their SDK 0.9.4. Espressif specific changes where reviewed, split in small, clean patches and applied on top of official LwIP git repository.

The Espressif original code was based on LwIP 1.4.0 with some cherry-picks so initial work for this project was also based on 1.4.0. After confirming that it's working, all the changes were rebased on 1.4.1.

This project does not contain complete LwIP stack. The code for network driver was not released by Espressif. Currently we only provide replacement for eagle_lwip_if.o from libmain.a. This module is responsible for setting up struct netif and calling netif_add() from LwIP.

Status

I've done some limited testing of this library - wifi works both in client and in AP mode and I had no problem with running esphttpd project. There is a need for more testing, of course. If you find any bug, please create an Issue or PR. Feel free to contact me by e-mail if you have any questions or suggestions.

Building

1. Clone the repo.
2. Make sure your gcc toolchain is in your PATH (I'm using esp-open-sdk)
3. Call make.
4. Put liblwip.a in your libraries path.

Changes compared to Espressif release

• The code is based on LwIP 1.4.1.
• All the options were moved to config/lwipopts.h file which was cleaned and simplified.
• The LwIP code is not marked with ICACHE_FLASH_ATTR but all the functions are moved to .irom0.text section using objcopy instead.
• Espressif changes to LwIP code was marked by LWIP_ESP macro.
• All Espressif specific code (dhcpserver, ping, espconn) are put in separate directory
• Small fixes.

Features added

• ESP_TIMEWAIT_THRESHOLD - available heap memory is checked on each TCP connection accepted. If it's below this threshold, memory is reclaimed by killing TCP connections in TIME-WAIT state.
• Our own eagle_lwip_if.o. It should do exactly what the original version does but is compiled from our code.
• LWIP_NETIF_HOSTNAME_PREFIX - if LWIP_NETIF_HOSTNAME is enabled, the device hostname that is raported to DHCP server will be set to LWIP_NETIF_HOSTNAME_PREFIX with hexadecimal representation of 3 least significant bytes of MAC address concatenated. This requires using our version of eagle_lwip_if.o.

eagle_lwip_if.o story

This object contains eagle_lwip_if_alloc() function which is called by SDK when network interfaces are created. It is responsible for allocating memory for struct netif and calling netif_add(). We need it because some of LwIP features, when enabled, will add additional fields to netif structure, changing its size and breaking SDK compatibility (Espressif version of eagle_lwip_if.o is compiled with their version of netif struct and will always allocate 56 bytes for it).

If you want to use it, you have to modify your libmain.a and either remove eagle_lwip_if.o from it and add our own version to liblwip.a (see USE_OUR_LWIP_IF in Makefile-local.mk) or replace it with our own version (see LIBMAIN_PATH in Makefile-local.mk).

Note that using or version of this module is not enough to freely change netif structure. It seems that it's used by some other parts of SDK too so we have to ensure that all the fields used by SDK are on expected offsets. We can freely add new fields at the end of this structure, though.

Makefile-local.mk

Use this file to create all the local modifications required to compile this library in your environment. There are also some options you can set there, see inline comments.