The ESP-IDF build system compiles all source files in the project and ESP-IDF, but only functions and variables that are actually referenced by the program are linked into the final binary. In some cases, it is necessary to reduce the total size of the firmware binary, e.g., in order to fit it into the available flash partition size.
To optimize both the firmware binary size and the memory usage, it is necessary to measure statically-allocated RAM (``data``, ``bss``), code (``text``), and read-only data (``rodata``) in your project.
Used static DRAM: 10608 bytes ( 170128 remain, 5.9% used)
.data size: 8464 bytes
.bss size: 2144 bytes
Used static IRAM: 48834 bytes ( 82238 remain, 37.3% used)
.text size: 47807 bytes
.vectors size: 1027 bytes
Used Flash size : 117391 bytes
.text: 80103 bytes
.rodata: 37032 bytes
Total image size: 174689 bytes (.bin may be padded larger)
-``Used static DRAM``: Total amount of DRAM allocated at compile time. ``remain`` indicates the amount of DRAM left to be used as heap memory at runtime. Note that due to meta data overhead, implementation constraints, and startup heap allocations, the actual size of the DRAM heap is smaller.
-``.data size``: Amount of DRAM allocated at compile time for the ``.data`` (i.e., all statically allocated variables that are initialized to non-zero values). ``.data`` also consumes space in the binary image to store the non-zero initialization values.
-``.bss size``: Amount of DRAM allocated at compile time for ``.bss`` (i.e., all statically allocated variables that are initialized to zero). ``.bss`` does not consume extra space in flash.
-``Used static IRAM``: Total amount of IRAM allocated at compile time. ``remain`` indicates the amount of IRAM left to be used as heap memory at runtime. Note that due to meta data overhead, implementation constraints, and startup heap allocations, the actual size of the IRAM heap is smaller.
-``.text size``: Amount of IRAM used for ``.text`` (i.e., all code that is executed from :ref:`IRAM <iram>`). ``.text`` also consumes space in the binary image as the code is initially stored there and is then copied over to IRAM on startup.
-``Used Flash size``: Total amount of flash used (excluding usage by DRAM and IRAM)
-``.text``: Amount of flash used for ``.text`` (i.e., all code that is executed via the flash cache, see :ref:`IROM <irom>`).
-``.rodata``: Amount of flash used for ``.rodata`` (i.e., read-only data that is loaded via the flash cache, see :ref:`DROM <drom>`).
-``Total image size`` is the estimated total size of the binary file.
..only:: not esp32
..code-block:: bash
$ idf.py size
[...]
Total sizes:
Used stat D/IRAM: 53743 bytes ( 122385 remain, 30.5% used)
.data size: 6504 bytes
.bss size: 1984 bytes
.text size: 44228 bytes
.vectors size: 1027 bytes
Used Flash size : 118879 bytes
.text: 83467 bytes
.rodata: 35156 bytes
Total image size: 170638 bytes (.bin may be padded larger)
-``Used stat D/IRAM``: Total amount of D/IRAM used at compile time. ``remain`` indicates the amount of D/IRAM left to be used as heap memory at runtime. Note that due to meta data overhead, implementation constraints, and startup heap allocations, the actual size of the DRAM heap is smaller.
-``.data size``: Amount of D/IRAM allocated at compile time for the ``.data`` (i.e., all statically allocated variables that are initialized to non-zero values). ``.data`` also consumes space in the binary image to store the non-zero initialization values.
-``.bss size``: Amount of D/IRAM allocated at compile time for ``.bss`` (i.e., all statically allocated variables that are initialized to zero). ``.bss`` does not consume extra space in flash.
-``.text size``: Amount of D/IRAM used for ``.text`` (i.e., all code that is executed from internal RAM). ``.text`` also consumes space in the binary image as the code is initially stored there and is then copied over to D/IRAM on startup.
-``Used Flash size``: Total amount of flash used (excluding usage by D/IRAM)
-``.text``: Amount of flash used for ``.text`` (i.e., all code that is executed via the flash cache, see :ref:`IROM <irom>`).
-``.rodata``: Amount of flash used for ``.rodata`` (i.e., read-only data that is loaded via the flash cache, see :ref:`DROM <drom>`).
-``Total image size`` is the estimated total size of the binary file.
The summary output provided by ``idf.py size`` does not give enough details to find the main contributor to excessive binary size. To analyze in detail, use ``idf.py size-components``.
The first lines of the output from ``idf.py size-components`` are the same as that from ``idf.py size``. After this, a table is printed as ``Per-archive contributions to ELF file``. This means how much each static library archive has contributed to the final binary size.
Generally, one static library archive is built per component, although some are binary libraries included by a particular component, for example, ``libnet80211.a`` is included by ``esp_wifi`` component. There are also toolchain libraries such as ``libc.a`` and ``libgcc.a`` listed here, these provide Standard C/C++ Library and toolchain built-in functionality.
If your project is simple and only has a ``main`` component, then all of the project's code will be shown under ``libmain.a``. If your project includes its own components (see :doc:`/api-guides/build-system`), then they will each be shown on a separate line.
-``DRAM .data & .bss & other`` - ``.data`` and ``.bss`` are the same as for the totals shown above. Both are static variables and reduce the total available RAM at runtime, but ``.bss`` does not contribute to the binary file size. ``other`` is a column for any custom section types that also contribute to RAM size. Usually, the value is 0.
:esp32:- ``IRAM`` - is the same as for the totals shown above. It refers to code linked to execute from IRAM, which uses space in the binary file and also reduces IRAM that can be dynamically allocated at runtime using ``HEAP_CAP_32BIT``.
:esp32:- ``D/IRAM`` - shows IRAM space which, due to occupying D/IRAM space, is also reducing available DRAM available as heap at runtime.
:not esp32:- ``IRAM`` - is the same as for the totals shown above. It refers to code linked to execute from IRAM, which uses space in the binary file and also reduces DRAM available as heap at runtime.
-``Flash code & rodata`` - these are the same as the totals above, IROM and DROM space accessed from the flash cache that contribute to the binary size.
For even more details, run ``idf.py size-files`` to get a summary of the contribution each object file has made to the final binary size. Each object file corresponds to a single source file.
The columns are the same as shown above for ``idy.py size-components``, but this time the granularity is the contribution of each individual object file to the binary size.
For example, we can see that the file ``x509_crt_bundle.S.o`` contributed 64,212 bytes to the total firmware size, all as ``.rodata`` in flash. Therefore we can guess that this application is using the :doc:`/api-reference/protocols/esp_crt_bundle` feature and not using this feature would save at last this many bytes from the firmware size.
Some of the object files are linked from binary libraries and therefore you will not find a corresponding source file. To locate which component a source file belongs to, it is generally possible to search in the ESP-IDF source tree or look in the :ref:`linker-map-file` for the full path.
To do so, first, locate the linker map file with the name ``PROJECTNAME.map`` in the build directory. The ``esp_idf_size`` tool performs its analysis based on the output of the linker map file.
For example, to compare two builds, one of which with the default :ref:`CONFIG_COMPILER_OPTIMIZATION` setting ``Debug (-Og)`` configuration while another with ``Optimize for size (-Os)``:
We can see from the ``Difference`` column that changing this one setting caused the whole binary to be over 60 KB smaller and over 5 KB more RAM is available.
If too much static memory is allocated, the linker will fail with an error such as ``DRAM segment data does not fit``, ``region `iram0_0_seg' overflowed by 44 bytes``, or similar.
In these cases, ``idf.py size`` will not succeed either. However, it is possible to run ``esp_idf_size`` manually to view the **partial static memory usage**. The memory usage will miss the variables that could not be linked, so there still appears to be some free space.
This is an advanced analysis method, but it can be very useful. Feel free to skip ahead to :ref:`reducing-overall-size` and possibly come back to this later.
The ``idf.py size`` analysis tools all work by parsing the GNU binutils ``linker map file``, which is a summary of everything the linker did when it created (i.e., linked) the final firmware binary file.
Linker map files themselves are plain text files, so it is possible to read them and find out exactly what the linker did. However, they are also very complex and long, often exceeding 100,000 lines.
-``Archive member included to satisfy reference by file (symbol)``
- This shows you: for each object file included in the link, what symbol (function or variable) was the linker searching for when it included that object file.
- If you are wondering why some object file in particular was included in the binary, this part may give a clue. This part can be used in conjunction with the ``Cross Reference Table`` at the end of the file.
Not every object file shown in this list ends up included in the final binary, some end up in the ``Discarded input sections`` list instead.
-``Allocating common symbols``
- This is a list of some global variables along with their sizes. Common symbols have a particular meaning in ELF binary files, but ESP-IDF does not make much use of them.
-``Discarded input sections``
- These sections were read by the linker as part of an object file to be linked into the final binary, but then nothing else referred to them, so they were discarded from the final binary.
- For ESP-IDF, this list can be very long, as we compile each function and static variable to a unique section in order to minimize the final binary size. Specifically, ESP-IDF uses compiler options ``-ffunction-sections -fdata-sections`` and linker option ``--gc-sections``.
- Items mentioned in this list **do not** contribute to the final binary.
-``Memory Configuration``, ``Linker script and memory map``
- These two parts go together. Some of the output comes directly from the linker command line and the Linker Script, both provided by :doc:`/api-guides/build-system`. The linker script is partially generated from the ESP-IDF project using the :doc:`/api-guides/linker-script-generation` feature.
- As the output of the ``Linker script and memory map`` part of the map unfolds, you can see each symbol (function or static variable) linked into the final binary along with its address (as a 16 digit hex number), its length (also in hex), and the library and object file it was linked from (which can be used to determine the component and the source file).
- Following all of the output sections that take up space in the final ``.bin`` file, the ``memory map`` also includes some sections in the ELF file that are only used for debugging, e.g., ELF sections ``.debug_*``, etc. These do not contribute to the final binary size. You can notice the address of these symbols is a very small number, starting from ``0x0000000000000000`` and counting up.
-``Cross Reference Table``
- This table shows the symbol (function or static variable) that the list of object file(s) refers to. If you are wondering why a particular thing is included in the binary, this will help determine what included it.
..note::
Unfortunately, the ``Cross Reference Table`` does not only include symbols that made it into the final binary. It also includes symbols in discarded sections. Therefore, just because something is shown here does not mean that it was included in the final binary - this needs to be checked separately.
Linker map files are generated by the GNU binutils linker ``ld``, not ESP-IDF. You can find additional information online about the linker map file format. This quick summary is written from the perspective of ESP-IDF build system in particular.
- Set :ref:`CONFIG_COMPILER_OPTIMIZATION` to ``Optimize for size (-Os)``. In some cases, ``Optimize for performance (-O2)`` will also reduce the binary size compared to the default. Note that if your code contains C or C++ Undefined Behavior then increasing the compiler optimization level may expose bugs that otherwise do not happen.
- Reduce the compiled-in log output by lowering the app :ref:`CONFIG_LOG_DEFAULT_LEVEL`. If the :ref:`CONFIG_LOG_MAXIMUM_LEVEL` is changed from the default then this setting controls the binary size instead. Reducing compiled-in logging reduces the number of strings in the binary, and also the code size of the calls to logging functions.
- Set the :ref:`CONFIG_COMPILER_OPTIMIZATION_ASSERTION_LEVEL` to ``Silent``. This avoids compiling in a dedicated assertion string and source file name for each assert that may fail. It is still possible to find the failed assert in the code by looking at the memory address where the assertion failed.
- Besides the :ref:`CONFIG_COMPILER_OPTIMIZATION_ASSERTION_LEVEL`, you can disable or silent the assertion for the HAL component separately by setting :ref:`CONFIG_HAL_DEFAULT_ASSERTION_LEVEL`. It is to notice that ESP-IDF lowers the HAL assertion level in bootloader to be silent even if :ref:`CONFIG_HAL_DEFAULT_ASSERTION_LEVEL` is set to full-assertion level. This is to reduce the bootloader size.
- Setting :ref:`CONFIG_COMPILER_OPTIMIZATION_CHECKS_SILENT` removes specific error messages for particular internal ESP-IDF error check macros. This may make it harder to debug some error conditions by reading the log output.
:esp32:- If the binary needs to run on only certain revision(s) of ESP32, increasing :ref:`CONFIG_ESP32_REV_MIN` to match can result in a reduced binary size. This will make a large difference if setting ESP32 minimum revision 3, and PSRAM is enabled.
:esp32c3:- If the binary needs to run on only certain revision(s) of ESP32-C3, increasing :ref:`CONFIG_ESP32C3_REV_MIN` to match can result in a reduced binary size. This is particularly true if setting ESP32-C3 minimum revision 3 and using Wi-Fi, as some functionality was moved to ROM code.
- Do not enable :ref:`CONFIG_COMPILER_CXX_EXCEPTIONS`, :ref:`CONFIG_COMPILER_CXX_RTTI`, or set the :ref:`CONFIG_COMPILER_STACK_CHECK_MODE` to Overall. All of these options are already disabled by default, but they have a large impact on binary size.
- Disabling :ref:`CONFIG_ESP_ERR_TO_NAME_LOOKUP` removes the lookup table to translate user-friendly names for error values (see :doc:`/api-guides/error-handling`) in error logs, etc. This saves some binary size, but error values will be printed as integers only.
- Setting :ref:`CONFIG_ESP_SYSTEM_PANIC` to ``Silent reboot`` saves a small amount of binary size, however this is **only** recommended if no one will use UART output to debug the device.
- If the application binary uses only one of the security versions of the protocomm component, then the support for others can be disabled to save some code size. The support can be disabled through :ref:`CONFIG_ESP_PROTOCOMM_SUPPORT_SECURITY_VERSION_0`, :ref:`CONFIG_ESP_PROTOCOMM_SUPPORT_SECURITY_VERSION_1` or :ref:`CONFIG_ESP_PROTOCOMM_SUPPORT_SECURITY_VERSION_2` respectively.
In addition to the many configuration items shown here, there are a number of configuration options where changing the option from the default increases binary size. These are not noted here. Where the increase is significant is usually noted in the configuration item help text.
- Disabling :ref:`CONFIG_ESP_WIFI_ENABLE_WPA3_SAE` will save some Wi-Fi binary size if WPA3 support is not needed. Note that WPA3 is mandatory for new Wi-Fi device certifications.
- Disabling ADC calibration features :ref:`CONFIG_ADC_CAL_EFUSE_TP_ENABLE`, :ref:`CONFIG_ADC_CAL_EFUSE_VREF_ENABLE`, :ref:`CONFIG_ADC_CAL_LUT_ENABLE` will save a small amount of binary size if ADC driver is used, at expense of accuracy.
- Disable either :ref:`CONFIG_BT_NIMBLE_ROLE_CENTRAL` or :ref:`CONFIG_BT_NIMBLE_ROLE_OBSERVER` if these roles are not needed.
- Reducing :ref:`CONFIG_BT_NIMBLE_LOG_LEVEL` can reduce binary size. Note that if the overall log level has been reduced as described above in :ref:`reducing-overall-size` then this also reduces the NimBLE log level.
- If IPv4 connectivity is not required, setting :ref:`CONFIG_LWIP_IPV4` to ``false`` will reduce the size of the lwIP, supporting IPv6-only TCP/IP stack.
Before disabling IPv4 support, please note that IPv6 only network environments are not ubiquitous and must be supported in the local network, e.g., by your internet service provider or using constrained local network settings.
Enabling the config option :ref:`CONFIG_NEWLIB_NANO_FORMAT` will switch Newlib to the "Nano" formatting mode. This is smaller in code size, and a large part of the implementation is compiled into the {IDF_TARGET_NAME} ROM, so it does not need to be included in the binary at all.
Disabling the config option :ref:`CONFIG_NEWLIB_NANO_FORMAT` will switch Newlib to the "full" formatting mode. This will reduce the binary size, as {IDF_TARGET_NAME} has the full formatting version of the functions in ROM, so it does not need to be included in the binary at all.
Enabling "Nano" formatting reduces the stack usage of each function that calls ``printf()`` or another string formatting function, see :ref:`optimize-stack-sizes`.
"Nano" formatting does not support 64-bit integers, or C99 formatting features. For a full list of restrictions, search for ``--enable-newlib-nano-formatted-io`` in the `Newlib README file`_.
Under **Component Config** > **mbedTLS**, there are multiple mbedTLS features enabled default, some of which can be disabled if not needed to save code size.
It is **strongly not recommended to disable all these mbedTLS options**. Only disable options of which you understand the functionality and are certain that it is not needed in the application. In particular:
- Ensure that any TLS server(s) the device connects to can still be used. If the server is controlled by a third party or a cloud service, it is recommended to ensure that the firmware supports at least two of the supported cipher suites in case one is disabled in a future update.
- Ensure that any TLS client(s) that connect to the device can still connect with supported/recommended cipher suites. Note that future versions of client operating systems may remove support for some features, so it is recommended to enable multiple supported cipher suites, or algorithms for redundancy.
If depending on third party clients or servers, always pay attention to announcements about future changes to supported TLS features. If not, the {IDF_TARGET_NAME} device may become inaccessible if support changes.
Enabling the config option :ref:`CONFIG_MBEDTLS_USE_CRYPTO_ROM_IMPL` will use the crypto algorithms from mbedTLS library inside the chip ROM.
Disabling the config option :ref:`CONFIG_MBEDTLS_USE_CRYPTO_ROM_IMPL` will use the crypto algorithms from the ESP-IDF mbedtls component library. This will increase the binary size (flash footprint).
Not every combination of mbedTLS compile-time config is tested in ESP-IDF. If you find a combination that fails to compile or function as expected, please report the details on `GitHub <https://github.com/espressif/esp-idf>`_.
:doc:`/api-reference/storage/vfs` feature in ESP-IDF allows multiple filesystem drivers and file-like peripheral drivers to be accessed using standard I/O functions (``open``, ``read``, ``write``, etc.) and C library functions (``fopen``, ``fread``, ``fwrite``, etc.). When filesystem or file-like peripheral driver functionality is not used in the application, this feature can be fully or partially disabled. VFS component provides the following configuration options:
*:ref:`CONFIG_VFS_SUPPORT_TERMIOS` — can be disabled if the application does not use ``termios`` family of functions. Currently, these functions are implemented only for UART VFS driver. Most applications can disable this option. Disabling this option reduces the code size by about 1.8 KB.
*:ref:`CONFIG_VFS_SUPPORT_SELECT` —can be disabled if the application does not use the ``select`` function with file descriptors. Currently, only the UART and eventfd VFS drivers implement ``select`` support. Note that when this option is disabled, ``select`` can still be used for socket file descriptors. Disabling this option reduces the code size by about 2.7 KB.
*:ref:`CONFIG_VFS_SUPPORT_DIR` — can be disabled if the application does not use directory-related functions, such as ``readdir`` (see the description of this option for the complete list). Applications that only open, read and write specific files and do not need to enumerate or create directories can disable this option, reducing the code size by 0.5 KB or more, depending on the filesystem drivers in use.
*:ref:`CONFIG_VFS_SUPPORT_IO` — can be disabled if the application does not use filesystems or file-like peripheral drivers. This disables all VFS functionality, including the three options mentioned above. When this option is disabled, :doc:`/api-reference/system/console` can not be used. Note that the application can still use standard I/O functions with socket file descriptors when this option is disabled. Compared to the default configuration, disabling this option reduces code size by about 9.4 KB.
:CONFIG_ESP_ROM_HAS_HAL_SYSTIMER:* Enabling :ref:`CONFIG_HAL_SYSTIMER_USE_ROM_IMPL` can reduce the IRAM usage and binary size by linking in the systimer HAL driver of ROM implementation.
:CONFIG_ESP_ROM_HAS_HAL_WDT:* Enabling :ref:`CONFIG_HAL_WDT_USE_ROM_IMPL` can reduce the IRAM usage and binary size by linking in the watchdog HAL driver of ROM implementation.
* Enabling :ref:`CONFIG_HEAP_PLACE_FUNCTION_INTO_FLASH` can reduce the IRAM usage and binary size by placing the entirety of the heap functionalities in flash memory.
:CONFIG_ESP_ROM_HAS_HEAP_TLSF:* Enabling :ref:`CONFIG_HEAP_TLSF_USE_ROM_IMPL` can reduce the IRAM usage and binary size by linking in the TLSF library of ROM implementation.
