Hi,

Yes, the libraries we provide (that come straight from the Espressif’s SDK) are compiled in a way that occupies most of the RAM. You can try hacking them (with extracting individual objects from .a files to .o files and renaming sections) to move some rarely functions from RAM to the IROM section.

We have also heard people disabling the instruction cache and successfully using another 32K block of RAM after the first 32K, but we have not tried it ourselves and are not aware of the potential performance or stability impact.

Sure, but please note that you do it at your own risk. Doing this may result in random crashes, bugs and strange behavior in production code.

1. Enable the generation of a .map file in VisualGDB Project Properties
2. Identify a particular symbol that you want to move to FLASH (json.a does not get included anywhere, so we’ll move ets_timer_arm_new that does). You can find the biggest symbols via Embedded Memory Explorer.
3. Build the project and locate the symbol in the linker script:

    .text          0x4010016c      0x3d8 f:\SysGCC\esp8266\esp8266-bsp/IoT-SDK/lib\libmain.a(ets_timer.o)
                                   0x450 (size before relaxing)
                   0x40100244                ets_timer_setfn
                   0x40100328                ets_timer_disarm
                   0x401003d8                ets_timer_arm_new

4. Copy libmain.a to libmain_fixed.a
5. Run the following commands to extract ets_timer.o from libmain_copy.a, rename .text to .irom0.text and put it back:

   xtensa-lx106-elf-ar x libmain_fixed.a ets_timer.o
   xtensa-lx106-elf-objcopy --rename-section .text=.irom0.text ets_timer.o
   xtensa-lx106-elf-ar r libmain_fixed.a ets_timer.o

6. Replace “main” with “main_fixed” in esp8266.mak (it will get reverted back once you edit anything in VisualGDB Project Properties, so you can instead rename libmain.a to libmain_orig.a and edit libmain.a).
7. Check the map file to see how it got moved to ROM:

    .irom0.text    0x40240000      0x3e4 f:\SysGCC\esp8266\esp8266-bsp/IoT-SDK/lib\libmain_fixed.a(ets_timer.o)
                                   0x450 (size before relaxing)
                   0x402400dc                ets_timer_setfn
                   0x402401c4                ets_timer_disarm
                   0x40240278                ets_timer_arm_new

Hi there,

It worked perfectly well with the ets_timer function. Unfortunately I ran into trouble trying function _divdi3.o, part of libgcc.a. A “dangerous relocation” error occured. It was suggested to add -mlongcalls to the compiler options, but no succes. Perhaps someone can give me a hint.
But perhaps better questions would be:
1: which know IRAM-functions can be relocated to flash? Perhaps there a list available?
2: Why did you select ets_timer as an example?

Thanks for the advise.
Following your procedure I got the message from the linker that the calling function “__udivmoddi4” could not “reach” the relocated functions. So then I tried to relocate function “__udivmoddi4”, but there was no reference to “__udivmoddi4” in the map-file to be found…

That was exactly what I did, but could not find any reference to udivmoddi4.
I repeated this procedure using the BlinkLed example, same result. perhaps you are able to find the reference?