Hi,
I am working with nRF52833 DK with nRF Connect SDK. All was going great until I had to add a GNU GSL library. I need it because I need matrix multiplications with complex numbers and eigen decomposition of matrices. When I added the the library code size exceeded FLASH size for 10 KB with linker error: arm-none-eabi/bin/ld.bfd: zephyr/zephyr_prebuilt.elf section `rodata' will not fit in region `FLASH'; arm-none-eabi/bin/ld.bfd: region `FLASH' overflowed by 10800 bytes.
So I started throwing code out that was not necessary (like printk), I minimized string constants of necessary printk statements, I used function for repeating code and used smaller data types (float instead of double and uint8_t instead of uint32_t). I managed to save 2.7 KB of code. But that is not enough. But I managed to get the code working with just excluding one of GSL functions that is less necessary. That gave me motivation so I took closer look at generated code.
I checked the generated zephyr.map file to see which functions take most of the space. I saw that some GNU GSL functions that I was clearly not using (and I am pretty sure that functions that I used do not use them) were compiled too. Like the ones in the provided screenshot. Functions like matrix multiplications for all possible types of matrices were included and I just used one of them. Including all this functions in the build is clearly why my code size exceeds FLASH size. I also included output of ninja rom report.
Is this because I cross-copiled GNU GSL library beforehand and I just included it in CMake build process or I just included library wrong in CMake build process? How can I get rid of these extra functions that eat my FLASH size? I cross-copiled GNU GSL library with command: ./configure --prefix=$HOME/opt/GNU_GSL_ARM_COMPILED --build=x86_64-unknown-linux-gnu --host=arm-none-eabi --target=arm-none-eabi CFLAGS="--specs=nosys.specs -mcpu=cortex-m4 -mthumb -mfloat-abi=hard -mfpu=fpv4-sp-d16". Below is included CMakeLists.txt file for how I included library in CMake process. Library is positioned in project_dir/src/gnu_gsl directory.
#
# Copyright (c) 2021 Nordic Semiconductor ASA
#
# SPDX-License-Identifier: Apache-2.0
cmake_minimum_required(VERSION 3.13.1)
set(GNU_GSL_LIB_DIR ${CMAKE_CURRENT_SOURCE_DIR}/src/gnu_gsl)
include_directories(${CMAKE_CURRENT_SOURCE_DIR}/src/gnu_gsl/include)
#add_subdirectory(${CMAKE_CURRENT_SOURCE_DIR}/src/gnu_gsl/include)
find_package(Zephyr REQUIRED HINTS $ENV{ZEPHYR_BASE})
project(direction_finding_connectionless_rx)
target_sources(app PRIVATE
src/main.c
)
add_library(gnu_gsl_lib STATIC IMPORTED GLOBAL)
set_target_properties(gnu_gsl_lib PROPERTIES IMPORTED_LOCATION ${GNU_GSL_LIB_DIR}/lib/libgsl.a)
target_link_libraries(app PUBLIC gnu_gsl_lib)
add_library(gnu_gslcblas_lib STATIC IMPORTED GLOBAL)
set_target_properties(gnu_gslcblas_lib PROPERTIES IMPORTED_LOCATION ${GNU_GSL_LIB_DIR}/lib/libgslcblas.a)
target_link_libraries(app PUBLIC gnu_gslcblas_lib)
Do you know any other tricks for code optimization for smaller size? I looked for -O optimization parameter of compiler but I do not know how to include it in CMake build process.
Can FLASH size be optimized with excluding some code? I tracked that someones are excluding bootloader for example. I searched for linker files but nRF Connect SKD works differently so I looked at dts files of board but I could not find any information on where different code sections are stored in FLASH.
I know that writing code for nearly full FLASH size is bad idea for future use but I currently do not have access to for example nRF5340 with bigger FLASH size. Also I think that with including just necessary functions from GNU GSL library my code size would be greatly reduced.
Any help would be appreciated.
Ales
