Sming No Wifi build option

[mikee47]

I recently came across https://basicengine.org/.

The BASIC Engine is a very low-cost single-board home computer with advanced 2D color graphics and sound capabilities, roughly comparable to late-1980s or early-1990s computers and video game consoles. It can be built at home without special skills or tools and using readily available components for under 10 Euros in parts, or mass-produced for even less."

It's an extraordinary project, but of interest here is its use of the ESP8266 without WiFi stack to release a ton of RAM. It uses https://github.com/pvvx/SDKnoWiFi.git to achieve this. There's also an Arduino Port.

I think it'd be rather handy to have this as a build option for Sming, but of course it would have to be done properly. SDKnoWiFi has a ton of low-level definitions and essentially re-implements the low-level support code for task queues, timers, etc. which the SDK normally does. I may end up doing that but as we'd need 100% compatibility with the existing SDK it seems like a lot of work and a little risky. (Although most of the code is floating about in various places it needs tidying up, checking, testing, etc.)

I've investigated some alternative approaches with the aim of hooking or patching the offending startup code within libmain.a itself, so that the linker discards all the wifi stuff we don't need and gives us the RAM back.

This seems simple enough - just replace calls to wifi_station_start and so on with no-ops or calls to dummy functions, but patching ELF object files is rather more involved and I'm disinclined to do that manually; I want a scripted approach.

[slaff]

just replace calls to wifi_station_start and so on with no-ops

So I guess you are not looking for the solution in NoWifiSDK: https://github.com/pvvx/SDKnoWiFi/blob/master/Makefile#L91-L100?

One thing that comes to my mind is that when the name and the signature of a function are known then you can do the following:

• describe all functions that need to be replaced with their unique name and function signature (params + return value). Put them in a yaml file (manual work)
• group the functions by signature. Let's call this function group (FG). (manual work - in the same yaml file)
• weaken the functions from the list based on their names (can be automated )
• create new file with one noop function per FGs. (can be automated)
• in the same file alias all functions to their FG noop functions (can be automated)

    int wifi_do_something(int x, int y) __attribute__((alias("noop_int_int_int")));

• during link time if the noWifiSDK was selected then include the noop file.

[mikee47]

Made a start on this, https://github.com/mikee47/Sming/tree/feature/no-wifi.

@slaff I haven't tried weakening functions, may give that a go if this doesn't pan out.

[slaff]

I haven't tried weakening functions,

GCC does that for you. For example rBoot is weakening Cache_Read_Enable_New in libmain:

xtensa-lx106-elf-objcopy -W Cache_Read_Enable_New libmain.a libmain2.a

[mikee47]

Done some further work on this and weakening helps in some situations so looks like a combination approach is working best. I'll open a PR shortly with progress as it's working for multiple samples now, including debugger :-)

[mikee47]

Getting the low-level functions into code is probably useful anyway general considering that the Non-OS SDK is now considered 'end of life'. I'm also continuing to migrate towards the RTOS headers. Arduino has imported all the SDK header files and only uses the pre-built libraries from the various SDK versions. This is a sensible move and we could dispense with the ESP8266_NONOS_SDK as a submodule.