Dzbj_ESP32-S3_Key/managed_components/espressif__cmake_utilities/docs/relinker.md

Relinker

In ESP-IDF, some functions are put in SRAM when link stage, the reason is that some functions are critical, we need to put them in SRAM to speed up the program, or the functions will be executed when the cache is disabled. But actually, some functions can be put into Flash, here, we provide a script to let the user set the functions which are located in SRAM by default to put them into Flash, in order to save more SRAM which can be used as heap region later. This happens in the linker stage, so we call it as relinker.

Use

In order to use this feature, you need to include the needed CMake file in your project's CMakeLists.txt after project(XXXX).

project(XXXX)

include(relinker)

The relinker feature is disabled by default, in order to use it, you need to enable the option CU_RELINKER_ENABLE in menuconfig.

Here are the default configuration files in the folder cmake_utilities/scripts/relinker/examples/esp32c2, it's just used as a reference. If you would like to use your own configuration files, please enable option CU_RELINKER_ENABLE_CUSTOMIZED_CONFIGURATION_FILES and set the path of your configuration files as following, this path is evaluated relative to the project root directory:

[*]     Enable customized relinker configuration files
(path of your configuration files) Customized relinker configuration files path

Note: Currently only esp32c2 is supported.

Configuration Files

You can refer to the files in the directory of cmake_utilities/scripts/relinker/examples/esp32c2:

• library.csv
• object.csv
• function.csv

For example, if you want to link function __getreent from SRAM to Flash, firstly you should add it to function.csv file as following:

libfreertos.a,tasks.c.obj,__getreent,

This means function __getreent is in object file tasks.c.obj, and object file tasks.c.obj is in library libfreertos.a.

If function __getreent depends on the option FREERTOS_PLACE_FUNCTIONS_INTO_FLASH in menuconfig, then it should be:

libfreertos.a,tasks.c.obj,__getreent,CONFIG_FREERTOS_PLACE_FUNCTIONS_INTO_FLASH

This means when only FREERTOS_PLACE_FUNCTIONS_INTO_FLASH is enabled in menuconfig, function __getreent will be linked from SRAM to Flash.

Next step you should add the path of the object file to object.csv:

libfreertos.a,tasks.c.obj,esp-idf/freertos/CMakeFiles/__idf_freertos.dir/FreeRTOS-Kernel/tasks.c.obj

This means the object file tasks.c.obj is in library libfreertos.a and its location is esp-idf/freertos/CMakeFiles/__idf_freertos.dir/FreeRTOS-Kernel/tasks.c.obj relative to directory of build.

Next step you should add path of library to library.csv:

libfreertos.a,./esp-idf/freertos/libfreertos.a

This means library libfreertos.a's location is ./esp-idf/freertos/libfreertos.a relative to build.

If above related data has exists in corresponding files, please don't add this repeatedly.