Esp8266 No WiFi

Background

Based on SDK 3.0.1 disassemblies with reference and thanks to:

The problem we have is to disentangle the wifi functions from the SDK within the app_main.o and user_interface.o modules from libmain.a. In particular, the user_start() code which mixes up wifi stuff with system code so it cannot be easily separated.

The SDKnoWiFi implements the startup code and some system functions but contains a lot of stuff which is provided by the SDK and in other parts of the Sming framework. We need to provide replacement functions to interoperate correctly with the remaining SDK code.

Advantages

  • Reduces code image size when networking/WiFi is not required

  • Eliminates need for SDK-specific partitions (rf_cal, phy_init, sys_param)

Process

This is the approach used to create this Component.

  1. Remove user_interface from libmain:

    ar d libmain.a user_interface.o

  2. Implement call_user_start_local. The actual entry point is call_user_start, in vector.o, which is required. (Note: This symbol was -u in the linker script but this is un-necessary and has been removed.)

  3. Build and implement missing functions.

Where functions can be passed directly to the ROM code (e.g. system_os_task -> ets_task) these are defined in the no.wifi.ld linker script.

Other code is located in a .c file named according to the module it replaces in libmain.a.

There are various options for integrating this into Sming, but I’ve decided the most useful way is to have it as a link-time option. We either link esp_wifi or esp_no_wifi as required, no rebuild to the framework is necessary. This is controlled by the DISABLE_WIFI setting.

This means that if there are any WiFi routines used in the project the link step will fail.

An alternate approach is to separate out the Network/WiFi stuff in the framework into separate Components which are themselves only included. However, some of the network code could be useful in a non-networked application. There may even be an alternate physical network layer implemented (e.g. Ethernet over SPI) so it’s simplest to just leave the framework intact.

Library Disassembly

You can create a disassembly of the relevant SDK libraries for inspection by running this command from a project directory:

make sdk-disassemble

If you want to disassemble other SDK libraries, do this:

make sdk-disassemble SDK_LIBLIST="crypto net80211"

Known issues

Further work is required to implement the following (list incomplete):

  • Sleep/power saving modes

  • Partition tables

  • Analogue reading

References

SoC support

  • esp8266